# Potting practises, frequency of repotting



## Bjorn (Nov 30, 2014)

Potting is necessary, but how do you guys practice it? According to "best practises" of paph growing, they should be repotted every two years or so. I never did that and most of my plants stay much longer in their pots. Traditionally I repotted when the plants started to sulk...
Recently, after starting fertilising at much lower levels I have noticed that root growth is better and that seemingly repotting is less necessary. Nowadays repotting is done at longer intervals and usually because the plant has outgrown its pot size.
Now, I wonder, what are the practises and experiences elsewhere?


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## Ozpaph (Nov 30, 2014)

about every two years. I find the mix goes off and the vigour slows. Also, I aim to have the plant 'outgrow' its pot in two years.


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## Brabantia (Nov 30, 2014)

In order to answer to your question definitely we should know (or remind of us) what you use as potting and which fertiliser you use, how much and with which frequency. If you often made potting flushing or not. In effect the stability of the potting mixture depends on these factors. Do not trust in the visual potting aspect.


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## Rick (Nov 30, 2014)

Since going to baskets, I've eliminated a lot of repotting hassle.

I still have stuff in pots, and have been experimenting with some systems that I gave up on years ago (like CHC mixes for barbata types).

In most cases I don't have a full 2 years on these trials since I didn't cut N application rates significantly more than 2 years back. But I am seeing results similar to yours Bjorn.


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## Justin (Nov 30, 2014)

agree there are many variables. i grow in fir bark mix and repot annually.


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## Rick (Nov 30, 2014)

I don't know if you remember that work by Xavier comparing Orchiata to other materials: But the type of material used makes a big difference on how much different fert components accumulate in the potting mix.

Orchiata accumulated roughly 1/2 the K compared to moss and coconut coir.

I suspect that would hold true for other metals like copper/zinc/iron/manganese that are in some fert mixes like MSU or Klite, and in general these are toxic to plants at lower concentrations than potassium.

So if buildup of toxic materials is the driver for repotting, the rate would be 1/2 for materials like Orchiata relative to coconut coir.


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## Erythrone (Nov 30, 2014)

Bjorn said:


> Potting is necessary, but how do you guys practice it? According to "best practises" of paph growing, they should be repotted every two years or so. I never did that and most of my plants stay much longer in their pots. Traditionally I repotted when the plants started to sulk...
> Recently, after starting fertilising at much lower levels I have noticed that root growth is better and that seemingly repotting is less necessary. Nowadays repotting is done at longer intervals and usually because the plant has outgrown its pot size.
> Now, I wonder, what are the practises and experiences elsewhere?



I've been on a 1 to 2 years repotting schedule for years. But there were some exceptions (some mature plantes in larger pots). I also waited about 10 years before trying to repot a Pinocchio. But it was too late  Like many ST members, I now fertilise at lower levels and I noticed I could delay repotting.


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## Rick (Nov 30, 2014)

Here's one of the more dramatic improvements via basket culture and starvation feeding.




This kolo was a pathetic virtually rootless 4" seedling when it went into the basket Dec 2010 (so almost 4 years ago). The wilhelm was also pretty sparse on roots going into the basket. It's coming back nicely too.

They were in this first group:
http://www.slippertalk.com/forum/showthread.php?t=18566&highlight=mark+date

You can see the original 4" basket the kolo was started in, and I just slipped it into a 6" basket when the roots started coming out the sides. The roots are already coming out of the 6" basket too.


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## naoki (Nov 30, 2014)

Good to hear what Bjorn is doing. When you repot after a couple years, are the media completely broken down? I think yours is similar to Birk's mix.

I have been doing yearly repot (bark based), but I started to think why do we need to do it. Accumulation of "stuff" (either salt or root excrete) and decay have been said to be the reason. The other possibility is the possible pathogenic micro-fauna.

- EC/TDS doesn't seem to increase too much with low fertilization scheme (I haven't tracked pH, and shift with pH could be a problem).
- Break down of media may increase the drying time, but if the drying time is not too excessive, we can just reduce the watering frequency. Breakdown can also provide some nutrients.
- Maybe, microbe supplement (cermi-compost tea, EM-1, Innocucor etc) may contribute to longer repotting intervals? They probably could increase the decay rate, but they may be reduce accumulation of "pathogenic" fauna if this ever happens. Also the root excrete could be reduced by beneficial fauna (pure speculation).


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## Rick (Nov 30, 2014)

Here's one of those root rotted lowiis from the group on the left. After I took the pic I repotted them all in fresh CHC mix.

http://www.slippertalk.com/forum/showthread.php?t=34792&highlight=tired

Not bad root growth for 3 1/2 months.

I'm going to try and kill it again. This time setting it up SH - hydroponically in glass beads, and try to refresh the solution daily with the 5ppm N feed I throw around the GH every day.


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## Brabantia (Nov 30, 2014)

@Rick about your Paphio Kolopakingii in basket.

Have you any data on pH and EC of your substrate measured by the pour through method using RO water or rain water?


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## Rick (Nov 30, 2014)

Brabantia said:


> @Rick about your Paphio Kolopakingii in basket.
> 
> Have you any data on pH and EC of your substrate measured by the pour through method using RO water or rain water?



Given that the substrate in the basket is mostly coarse limestone gravel (with moss around the edges, and water only stays in it for a short time there is probably very little buildup of minerals. This is very close to a mounted condition. I suspect I would have to pour the RO through several times to get a measurable number on my home meter. The most holdup would be in the moss, but it is probably not homogeneous throughout the basket. There is very little moss on the bottom, and a fair amount of exposed roots not in contact with substrate.

If I get ambitious I'll try to set something up to test.

The EC of the daily fertigation water is 60 - 80 uS/cm and pH about 6 the last time I checked.


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## gonewild (Nov 30, 2014)

Rick said:


> I'm going to try and kill it again. This time setting it up SH - hydroponically in glass beads, and try to refresh the solution daily with the 5ppm N feed I throw around the GH every day.



If it dies blame in on Silica toxicity.


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## Stone (Nov 30, 2014)

Rick said:


> I'm going to try and kill it again. This time setting it up SH - hydroponically in glass beads, and try to refresh the solution daily with the 5ppm N feed I throw around the GH every day.



You might have trouble with the base of the not getting enough moisture an there is no capillary action from the glass?


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## Stone (Nov 30, 2014)

Rick said:


> I don't know if you remember that work by Xavier comparing Orchiata to other materials: But the type of material used makes a big difference on how much different fert components accumulate in the potting mix.
> 
> Orchiata accumulated roughly 1/2 the K compared to moss and coconut coir.
> 
> ...



I agree that you need to understand the media you use. I think CHC should get VERY low fert levels where as my brachys in lava and diatomite get plenty and are thriving. (sat in shallow water and in theory should not need repotting until ( I hope) they are bursting out.
Orchiata falls somewhere in between the 2 extremes?


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## Rick (Nov 30, 2014)

Stone said:


> You might have trouble with the base of the not getting enough moisture an there is no capillary action from the glass?



Will have to see, and play with the depth. Also when I refresh I'll pour through the pot, which will re wet the upper roots. There's some roots all the way to the bottom and they'll be constantly submersed.

Also its in the GH with high humidity. I have some lowii in very open baskets with some roots totally free of substrate and still growing fine. 

I'm a tad more concerned about the constantly wet roots than the dry roots.

If this was a phrag I wouldn't think twice about this.


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## Bjorn (Dec 1, 2014)

Naoki, Rick, and everyone else that bothers, look into this approach on why low amounts of fertilisers make potting mixes last longer.

I think it is fair to say that one common experience is that when fertilising at lower levels, the potting intervals may be increased. The explanation involves the CEC (cation exchange capacity) of the substrate, or perhaps we should call it CAC(cation absorbtion capacity). Why? let me explain:

Most colloids and many organic structures like sphagnum, bark and CHC has active sites with the ability to dissociate and produce negative charges on the surface, which subsequently get some cation adsorbed. This is the way many (most) plants gets their cations; by removing a cation from its absorbed site, replacing it with a hydrogen ion (H+). That way charges are kept neutral.

Many components of the potting mix, particularly sphagnum, have these sites predominantly in the hydrogen form, i.e. no other added cation than hydrogen.
Once these sites are subjected to a liquid containing cations, e.g. potassium or calcium, the potassium or calcium replace the hydrogen and the moss liberates a certain amount of H+. This is acid and that is one of the reasons why e.g. sphagnum has an acid reaction in water.

Ok, after a while with fertilisers, all the sites are occupied with cations - which ones are dependent on their ability (concentration) and the size and charge of the ion. Generally polyvalent ions have smaller ionic radius than monovalent, so Ca2+ would replace K+ if fed at the same amount. But traditionally the content of calcium was not as high as that of potassium, so generally most sites would be occupied with potassium. Over time, when the substrate breaks down, more colloids are produced with more active sites that can adsorb cations. Over time, the amount of adsorbed cations can be quite high, and remember, this is adsorbed and will not be liberated unless they are exchanged by eg. acid. So measuring the amount by "pour through" will not measure it unless you pour through an acid.

If for instance you fertilise on a weekly basis, since the fertiliser probably is more acid than your normal water, this fertiliser may release quite a lot of cations and you might have a situation that suddenly gets more or less poisonous for your roots due to a massive liberation of cations. This will be primarily potassium I suspect, since once polyvalent ions like calcium adsorb, they will have excess charges available and the posibility of neutralising two negative sites. This can be done by linking two colloids. A typical example of this kind of reaction is stabilisation of clay by lime. The effect of that action is that the cations both gets immobilised and also that the colloids transform to an earth-like structure (this is soil).

If we restrict the amount of monovalent ions relative to polyvalent, e.g increase the amount of calcium and magnesium (and the micros for that sake) relative to potassium (and probably ammonium, NH4+), then the sites will be occupied by e.g. calcium , the calcium replaces potassium being adsobed.
A nice explanation to this is given in the link below:
http://www.terragis.bees.unsw.edu.au/terraGIS_soil/sp_exchangeable_cations.html
If your fertiliser contain ammonium, NH4+, that ion will compete with the potassium getting adsorbed. The adsorption Properties are similar, but a little more ammonium than potassium gets adsorbed: http://www.ipipotash.org/udocs/Interaction_of_Potassium_and_Ammonium_ions_in_Soil.pdf

What is the effect of all this? Simply that if the levels of potassium is kept low relative to calcium, then less gets adsorbed and the likelyhood of later getting a massive liberation is reduced. Also since some potassium is needed you cannot remove it entirely, but if the fertiliser contain ammonium, then adsorbtion of potassium is further reduced.(its probably much more complex than this but this is my interpretation).

If you start with a potting mixt that has a low CEC i.e. stay away from sphagnum and CHC, then things may work fine for a long time. If the bark is treated with calcium (Orchiata) then even better, and if you use a fertiliser with proportionally more calcium/magnesium than potassium, it would help as well. And last, ammonium helps also.

Comments?


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## monocotman (Dec 1, 2014)

*compost breakdown*

Bjorn,

there is possibly another thing to consider. 
The effect of bacterial growth within the medium. 
They grow and breakdown organic composts in proportion to the amount of nitrogen given to them.
Therefore giving less means they grow and breakdown the compost more slowly and it therefore last longer.
Is this correct or am I missing something?

David


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## Stone (Dec 1, 2014)

I agree with most of your interpretation. However I am yet to be convinced that lack of Calcium is very often a much of a problem. I think there is too much emphasis put on it.

My view:
I have been growing plants of all kinds for many years. Cacti, orchids, trees, shrubs, citrus, ferns, cycads, bromeliads, blah blah. No exageration to say I cannot ever remember seeing a classic example of Calcium deficiency ever! The plants grew well with good roots, leaves and flowering. Plants grown in a general ground bark mix with a medium CEC. Some desert plants which grow on pure hard limestone with no humus in the habitat did just as well as any others without added lime.

If fact even these plants resent lime in the medium. Until recently I had never used fertilizers with calcium of any kind in them and always with high potassium as well. The only Ca they ever saw was coming from the tap water. And it seems that this was more than enough. The only consistant problem was with citrus species lacking Mg but they are very prone to this anyway.

I also read somewhere that much of the Ca in Calnitrate becomes unavailable to the plant by forming insoluble Calcium carbonate. I don't know whether this is true or not but if it is it would further convince me that we just do not need to add much Ca. I had not used it in the past. I do now because I am aiming for a 75/25 nitrate / ammonuim ratio because many trials recommend this.

I have posted before some Dutch hydroponic data for a range of crops which recommends Ca additions (to rockwool substrate) of around one half of potassium in all cases for optimum results. EC varies according to crop senstivity to salinity. Why do we feel that orchids are so different in their nutrient ratios? EG; Phrags grow in the same general habitat as Anthurium.
Anthuriums are grown to perfection hydroponically with the above kind of nutrient formulations.

Don't we need to look at the big picture? I am begining to think we should take more notice of the growth response of the plant rather than worrying too much about superficial and incomplete theories about Ca content of leaves and habitat data.

Sorry Bjorn, this may not have much to do with your initial subject
But generally I think at least we all agree that the higher the CEC of the mix, the less overall feeding is needed. Lower additions of cations is necessary and probably frequent repotting is desirable to bring everything back to square one?


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## Stone (Dec 1, 2014)

monocotman said:


> Bjorn,
> 
> there is possibly another thing to consider.
> The effect of bacterial growth within the medium.
> ...



That is correct as I understand it. But the plant also sees less N and sometimes not enough.


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## Bjorn (Dec 1, 2014)

Mike, re the post above on calcium; I might have been unclear, but in my perception, the calcium is protecting the plants from sudden K poisoning not by being taken up by the plant, but by preventing K to accumulate in the colloids. That way, no effect would be seen on the plant growth. No deficiency symptoms in other words. If you have lime in your water (hard water) calcium supply should normally be sufficient anyhow.


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## Bjorn (Dec 1, 2014)

Re the microbial situation. Could make sense that microbial action is accelerated by fertiliser. By the microbial activity, the colloid are produced and a high activity produces more, potentially harmful colloids. If they adsorb K of course. I have many pots recently that have entirely broken Down substrate that has perfectly healthy roots, almost without substrate!


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## Brabantia (Dec 1, 2014)

Thanks Rick for your fast response and thank you also for the other participants at this very interesting discussion.
Here are some data I taked this morning on some of my plants.




.

The plants are cultivated in a substrate made with70% bark/30% CHC at which I added 10% of small expanded clay balls. No dolomitic material added. As fertilyser I use a 4/1/1 NPK (not N/P2O5/K2O). The ratio NNO3-/NNH4+ is 85%/15%. I fertilise at 40 ppm N one time per week. At this Nitrogen concentration the one in Ca++ and Mg ++ is 30 ppm and 10 ppm respectively. Water used: rain water always.
Measured EC of the fertilyser solution ~ 350 µS. pH adjusted to 6 with KOH 1M.
Here are my conclusions after two years of culture using these conditions.
Using low or medium level of fertilisation with a fertilyser having a high proportion of Nitrogen in the nitrate form cannot regulate tightly the substrate acidification. 
Because the high humidity, the presence of nitrate (an oxidizing agent) and the bacteries developpement, all these factors (and many more other for sure) leads to a situation where the substrate becomes acid and sometimes very acid.
This situation can be attained in the short or medium terms. (6 months to one year)
I have no data about the ideal pH for nitrates assimilation but in culture In-Vitro it is common to use a pH between 5.7 and 6.
My understanding of the reasons for which it is necessary as often to repot are : 
The acidification of the substrate below 5.5 do not allow the nitrogen assimilation (and maybe other minor elements) and stop the plant developpement . 
The acidification create an environment favourable for the roots rot.
In my opinion (IMHO) this is the raison why Rick has so good results with so low nitrogen distribution and using a substrate made mainly with dolomitic stones mixed with some mousse ... the pH of its substrate is stabilized and the Nitrogen assimilation is thus optimized.
Maybe in the future we shall come back on the necessity of granular dolomite addition in paphiopedilums substrate. Not as a Calcium Magnesium source as it was recommended in former days but because its pH stabilization properties.
Your comments will be highly appreciated.


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## Brabantia (Dec 1, 2014)

Here is what I noticed from the points of view health and flowering of plants.
More flowering ... due to the decrease in fertilisation (lower N and K concentrations) but more regularly (one time per week) and a better control of the potting humidity.
But ... the growth rates is very slow, many plants lose their leaves (the older leaves ... translocation) and the new leaves never reached the size of the leaves of the older shoots, the one when I bought the plant. 
In conclusion the plants are regressing!


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## Rick (Dec 1, 2014)

monocotman said:


> Bjorn,
> 
> there is possibly another thing to consider.
> The effect of bacterial growth within the medium.
> ...



This one I agree is the biggest factor with regard to mix "breakdown".

The CEC component causes mixes to become intolerant (toxic) faster, but shouldn't directly change the breakdown rate of the mix.


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## Rick (Dec 1, 2014)

Brabantia said:


> The acidification create an environment favourable for the roots rot.
> In my opinion (IMHO) this is the raison why Rick has so good results with so low nitrogen distribution and using a substrate made mainly with dolomitic stones mixed with some mousse ... the pH of its substrate is stabilized and the Nitrogen assimilation is thus optimized.
> Maybe in the future we shall come back on the necessity of granular dolomite addition in paphiopedilums substrate. Not as a Calcium Magnesium source as it was recommended in former days but because its pH stabilization properties.
> Your comments will be highly appreciated.



I would disagree that the stone in my baskets is the cause of pH stabilization. The pieces are too hard and large for significant pH control.
If I used a more friable/granular product then I would get pH stabilization, but in my case I just get drainage. 

However I agree that reduced nitrate input (and increased aeration) supports much less microbiology that runs the pH down. Wang presented work that indicated as such by comparing pH of fed versus unfed moss substrates. The unfed moss pH stabilized at > 5.0 while the fed substrate dropped continuously during the trial (I can't recall how far below 4.0 s.u.). Adding a plant made it even worse. The carbohydrate exudates of a heavily feed plant seemed to add fuel to the acid production of the microflora.


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## Rick (Dec 1, 2014)

Bjorn said:


> Re the microbial situation. Could make sense that microbial action is accelerated by fertiliser. By the microbial activity, the colloid are produced and a high activity produces more, potentially harmful colloids. If they adsorb K of course. I have many pots recently that have entirely broken Down substrate that has perfectly healthy roots, almost without substrate!



Very little K is taken up by microbes. Which is why Xavier showed increase in K with the different mixes.

These bacteria are the same as for the wastewater species we use for sewer plants. We can't get any appreciable uptake of K, even though we would like to reduce it on influent waste streams.


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## naoki (Dec 1, 2014)

Lots of interesting ideas, Bjorn! A lot of things you mentioned is something I haven't thought about, but it does make sense (even though I don't know about chemistry as much as you do).

One thing I'm not sure about is what you said about the pour-through. Is it true that once cations are attached to a negative site, it doesn't get released, so pour-through can't detect it? I have thought that the bind is more dynamic than static. I looked at a paper measuring the CEC of pine bark (Thomas and Perry. 1980. Ammonium nitrogen accumulation and leaching from an all pine bark medium. HortSicence 15: 824-825). And you are right, there are some cations which can't be removed by leaching by water, but the amount seems to be pretty small. They soaked bark in DI water for 72 hours. Then they put barks into a column, and started to drip 200 ppm N ammonium sulfate, and measured ppmN of drips from the bottom of the column. Then they leached with water after the output ppmN reached to the equilibrium (around 192 ppmN). Majority of N get leached out, but 1.94% of the total applied N remained in the bark. With sphags, maybe these unreachable cations could be high and cause the problems you are talking about.

Now, my question is how much the sudden release of cations contributes to raised EC (or osmotic pressure is what roots really care). If it is really a problem, can't we detect the increase in the EC of pour through after pouring the fertilizer (i.e compare the EC of fertilizer and EC of pour-through with the fertilizer)?

Brabantia, so pH and EC seems to be pretty stable. As Rick mentioned about the Sphag moss acidification study (Yen et al. 2011, HortScience 46(7):1022-1026), the authors concluded that the main cause of pH decline was due to the root excretion (there are some contribution from types of substrate and whether the fertilizers are applied, but the authors considered that these other factors to be minor). Then, they conclude that low pH is not an issue for the production of Phalaenopsis (Paphs would be possibly different) since the growth of Phals were normal (even around pH of 3-4).


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## Rick (Dec 1, 2014)

naoki said:


> Brabantia, so pH and EC seems to be pretty stable. As Rick mentioned about the Sphag moss acidification study (Yen et al. 2011, HortScience 46(7):1022-1026), the authors concluded that the main cause of pH decline was due to the root excretion (there are some contribution from types of substrate and whether the fertilizers are applied, but the authors considered that these other factors to be minor).



That's a different conclusion from what I got (especially from fig 1).

-Moss with no plant or fert stayed at average of 5.0 su (after initial drop to ~ 4.0).
-Moss with plant but 0 fert went from 5.0 to leveling off average of between 3.5 to 4.0
-Moss with no plant but fert added immediately went to pH 3.8 and eventually crept down to ~ 3.5 (almost no change just constantly low). 
-Moss +plant +feed started at the same spot as the fed only pot (about 3.8) and eventually declined to about ~3.0.

So over 1 pH s.u drop just adding N in the first place, but plants contributed another 1s.u drop to the fed and unfed condition.

I believe N rate was 200ppm in these trials and the trial length was only 30 weeks. Peak lows by 12-15 weeks after which seemed either leveling off or recovery.


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## Rick (Dec 1, 2014)

I think the conductivity track on these trials was interesting too.

If we equate EC with "food". Then it appeared that only a tiny amount of "food" was "consumed" by the plant.

The EC of unfed moss, or moss w/unfed plant was 0.0dS/m

The EC of the fed conditions was 1.25dS initially and climbed to almost 2dS for the no plant pot, but stayed level at 1.25dS for the fed + plant condition.

The difference (0.75dS) at the end of 30 weeks would be combined plant and microflora uptake. This difference suggests that only 38% of what went into the pot was taken up by anything (plant or microflora).


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## Rick (Dec 1, 2014)

Brabantia said:


> The plants are cultivated in a substrate made with70% bark/30% CHC at which I added 10% of small expanded clay balls. No dolomitic material added. As fertilyser I use a 4/1/1 NPK (not N/P2O5/K2O). The ratio NNO3-/NNH4+ is 85%/15%. I fertilise at 40 ppm N one time per week. At this Nitrogen concentration the one in Ca++ and Mg ++ is 30 ppm and 10 ppm respectively. Water used: rain water always.
> Measured EC of the fertilyser solution ~ 350 µS. pH adjusted to 6 with KOH 1M.



Brabantia. Where does your Ca and Mg come from? Also ammonia is antagonistic with K, Ca, and Mg. And bacterial nitrification of ammonia consumes alkalinity like crazy. With 6 ppm of your 40ppm N total in ammonia, that's a ton of bug food, and a big chunk of alkalinity reduction.

I think your K input is still to high. At 4-1-1 with N at 40, but adding KOH to adjust for pH that's still at least 10 ppm K ( and 10 times the K concentration in PK root water in situ). With K lite at 40 ppm K is down to ~3 ppm. Still 3 x higher than what PK see in the wild, but getting into the realm of natural surface waters. 

I'm pretty convinced that even 40ppm (assuming you are saturating the pots at each feeding) is still way to much. Why don't you try 10ppmN for a while?

I'm pretty sure Mou Zong-min paper on Nitrogen requirements for P armeniacum was linked a ways back by Naoki, but doing the math. 

They fed 50 ml of up too 420mg/L N solution into already saturated 785 ml pots. ONCE A MONTH.

Simple math. Each pot received 0.05 L of solution (21 mg) spread out into a 785 ml mass of wet moss (26 mg/L).

Not accounting for microflora competition, that averages 0.89 mg/pot per day (or 6.2 ppm per weekly dose). (Now we are back to insitu PK root water concentrations)

Also that was the high concentration. "Optimal" concentration varied from 105 to 420 ppm N solution strength depending on the parameter( vegetative growth versus seed germination rates for examples). The plants did fine from 0 to 420 ppm N solution strength. Just some parameters better than others.

So when figuring dose need to include more than just ratios and solution strength into the equation. It doesn't take much to make the orchids happy.


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## Bjorn (Dec 2, 2014)

Rick said:


> That's a different conclusion from what I got (especially from fig 1).
> 
> -Moss with no plant or fert stayed at average of 5.0 su (after initial drop to ~ 4.0).
> -Moss with plant but 0 fert went from 5.0 to leveling off average of between 3.5 to 4.0
> ...



This is exactly what I try to explain in that long thead above. The moss has hydrogenated sites. When you add fertiliser, the cations that adsorb on the moss releases H+ which is acid. Additionally, there is some acidification by the roots excreting H+ to get to the adsorbed cations.
Just one thing we should remember; pH is the negative logarith of the H+ concentration, so a pH of 4 signifies 10 times more H+ than does a pH of 5. You all know that, but its good to remember.


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## Bjorn (Dec 2, 2014)

Rick said:


> Very little K is taken up by microbes. Which is why Xavier showed increase in K with the different mixes.
> 
> These bacteria are the same as for the wastewater species we use for sewer plants. We can't get any appreciable uptake of K, even though we would like to reduce it on influent waste streams.



You are too hooked up in micro-organisms, Rick. I am talking about colloids, micro and nano-sized particles that is the building stone of soil and the result of microbial break-down of e.g. bark.

These colloids that are typical for a broken-down mix has a significant CEC, much more than bark etc. Since calcium bonds much stronger to these colloids than potassium, sufficient calcium in the fertiliser can retard or block potassium adsorption. If potassium accumulates, a brief lowering of pH, eg by fertilising, can release large amounts that may not be very good for your roots.

The microbes have a part in this picture as well, but they are just consuming nutrients and producing colloids and what else they produce.

It is perfectly possible to grow paphiopedilums in pots with totally broken down compost. I have seen several examples of pots being filled with roots only and just a bit of remains of the original compost. Without root-rot.


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## gonewild (Dec 2, 2014)

Bjorn said:


> It is perfectly possible to grow paphiopedilums in pots with totally broken down compost. I have seen several examples of pots being filled with roots only and just a bit of remains of the original compost. Without root-rot.



And for each one of the examples you saw 1000 other plants did not survive the same declining conditions.

If a plant is able to grow a mass of roots before the media declines then it does fine. Why? Because the roots of orchids do not require solid media. They need humid space between solid objects like a crack in a rock, space between stones or wood, space between moss foliage or 2/3 of the root exposed to air while the other 1/3 is sucking onto tree bark.

What do you think the survival rate would be for Paph seedlings potted up into pots filled with totally broken down media?


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## Bjorn (Dec 2, 2014)

gonewild said:


> And for each one of the examples you saw 1000 other plants did not survive the same declining conditions.
> 
> If a plant is able to grow a mass of roots before the media declines then it does fine. Why? Because the roots of orchids do not require solid media. They need humid space between solid objects like a crack in a rock, space between stones or wood, space between moss foliage or 2/3 of the root exposed to air while the other 1/3 is sucking onto tree bark.
> 
> What do you think the survival rate would be for Paph seedlings potted up into pots filled with totally broken down media?



And since some survive, there must be a reason for the death of the 1000. Why do those 1000 plants die? how can we improve the survival rate? I believe much can be done by a combined increase in Ca/Mg with a reduction in potassium. Actually much what Rick is doing, but from a slightly different angle. 
Growing in an entirely broken down media? no idea, perhaps if you could make it really well aerated and free of pathogens?? After all, we do not want to kill those seedlings. I think I have to try with some leaf-mulch one day, has to be pristine from the forest floor, not a chemically infused mush from any pot. Wrong fertiliser routines destroy the mush, making it poisonous. That is what I try to explain.
Anecdotal: I used to have a tray in which I grew P. micranthum with great success for 10-12years without repotting. Sorry to say but the bark based mix got quite mushy after all those years. The plants did not suffer until I started fertilising and after two years the whole thing collapsed. Why? was it because the mix could take 10-12 years only? or was it because I started feeding (at 3-400ppm)


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## gonewild (Dec 2, 2014)

Bjorn said:


> And since some survive, there must be a reason for the death of the 1000. Why do those 1000 plants die?


 
Good question. Perhaps it's part of genetics that leads to evolutionary change. Maybe the one survivor just grew fast enough to be past the need for the media by the time the media became bad. Maybe the 1000 died because of the same conditions that caused the media to become bad??????

how can we improve the survival rate? 

That was the focus on reducing the K levels. Now that some positive results have been observed different ideas are coming up, perhaps it's not the K but another element? The way we can improve the survival rate is to keep an open mind and try new ideas. Don't just fall back and rely on published science assuming the researchers knew what they were doing.



> I believe much can be done by a combined increase in Ca/Mg with a reduction in potassium. Actually much what Rick is doing, but from a slightly different angle.



Very much worth continuing with your direction.




> Growing in an entirely broken down media? no idea, perhaps if you could make it really well aerated and free of pathogens??



Then it would no longer be a broken down media.



> After all, we do not want to kill those seedlings.



NO we don't! That's why we want to look at new ideas that have not been tried. Because so far most media breaks down quickly and that results in the decline in plant health and survival.



> I think I have to try with some leaf-mulch one day, has to be pristine from the forest floor, not a chemically infused mush from any pot.



Can I suggest that you not waste your time trying methods and ideas that have already been tried? Leaf mulch was abandoned many maney years ago as a viable media for container culture.



> Wrong fertiliser routines destroy the mush, making it poisonous. That is what I try to explain.



Agreed. That is why Rick looked at K levels. Now you suggest perhaps Ca/Mg may play a more major role. So focus on the elements not the leaf litter. What in leaf litter might make a difference? What around the roots makes a difference? 
Looking at what is around the roots is why I started saying most of the nutrients for orchids are coming from organisms and not dissolved salts in runoff water. How and where do the orchids get their Ca/Mg? Figure it out! I've tested water flowing over moss covered limestone here in Peru and get 0.0 ec reading so the calcium from limestone is not in the water as a salt.



> Anecdotal: I used to have a tray in which I grew P. micranthum with great success for 10-12years without repotting. Sorry to say but the bark based mix got quite mushy after all those years. The plants did not suffer until I started fertilising and after two years the whole thing collapsed. Why? was it because the mix could take 10-12 years only? or was it because I started feeding (at 3-400ppm)



My guess is your media may have lasted forever had you not killed the organisms that had established in your micro environment when you added salts. :sob:


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## troy (Dec 2, 2014)

I repot all my plants in clear airy pots when they outgrow the pots they are in but after a few days I look they are bone dry, I don't soak the new media, should I flush The pot, I use straight ro water another question ro water is unstable how could I stabilize it?


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## troy (Dec 2, 2014)

Gonewild, I read yur message got me thinking awhile back I started using only organics and it's worked very well for me although I do beleive there are still salts in it, what do you fertilize with? And what potting media do you use?


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## gonewild (Dec 2, 2014)

troy said:


> Gonewild, I read yur message got me thinking awhile back I started using only organics and it's worked very well for me although I do beleive there are still salts in it, what do you fertilize with? And what potting media do you use?



Yes organics have dissolved salts much like commercial chemical fertilizers.

I use chemical fertilizers. 
Historically I used maximum doses of nutrients every time I watered to grow plants as big and fast as possible. It works very well. But over the years of growing I observed various disease and plant health problems with plants that were grown "forced" for extended periods of time. I never associated the growth problems with excess nutrients until Rick proposed the Potassium toxicity concept and suggested that he noticed less rot with less potassium. He had enough observational success that I tried it myself and also noticed an improvement in the "disease" issue.
It became obvious to me that the disease was not a disease at all but instead it is a result of the plant reacting to an overdose of nutrients. 
Does not matter if the nutrients come from chemical or organic fertilizer once the nutrients are dissolved they are basically the same salts in the water.

Now I am experimenting with various combinations of nutrients and so far I am in agreement that lowering the potassium level in fertilizer is a huge advance in plant/nutrient health quality.

Without doubt using low levels of potassium is better than high levels, that I have proved to myself.

I have grown in just about every type of media and can say that media type is not the main issue. You can grow an orchid in or on almost any material as long as you adjust the water and nutrients to adapt to the media. That's not to say that all medias work well! In my opinion the best media is a media that is alive and not dead, but that is pretty difficult to manage in a small space. 
Right now my main ingredient in my substrate is Brazilnut shells and that may or may not have been a good idea.
But it is giving me insight and answers about potassium toxicity.

I don't like growing in bark medias because they breakdown too quickly. So far the best mixture that I have found was a mix of Leca, CHC, charcoal and pumice. It holds moisture but is very open and has air space. In an open airy media it is easy to repot more often as the media decomposes.


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## Brabantia (Dec 2, 2014)

Rick said:


> Brabantia. Where does your Ca and Mg come from?


From Calcium nitrate (YARA) and Magnesium nitrate (PA).


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## NYEric (Dec 2, 2014)

Repot!? Does that have something to do with marijuana!?


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## Brabantia (Dec 2, 2014)

NYEric said:


> Repot!? Does that have something to do with marijuana!?


You know probably rePotme.com?


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## troy (Dec 2, 2014)

Wonder what would be a hrsher crime having a joint in colorado or a 2 liter bottle of soda in new york?


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## Ray (Dec 2, 2014)

Bjorn said:


> Re the microbial situation. Could make sense that microbial action is accelerated by fertiliser.




That's an absolute fact. Nitrogen plus a carbon source causes the colony to explode.

The petrochem company I work for used a high-N / olive oil emulsion to remediate some of the Exxon Vadez spill. The spray accelerated the native bacterial growth, and when the olive oil was gone, they went to work on the spill. All traces were gone within 6 weeks.


Ray Barkalow
firstrays.com


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## Bjorn (Dec 2, 2014)

Ray said:


> That's an absolute fact. Nitrogen plus a carbon source causes the colony to explode.
> 
> The petrochem company I work for used a high-N / olive oil emulsion to remediate some of the Exxon Vadez spill. The spray accelerated the native bacterial growth, and when the olive oil was gone, they went to work on the spill. All traces were gone within 6 weeks.
> 
> ...



No problem with that, but why is the decomposed bark mix so detrimental? Sometimes it is and sometimes its not, but why?

Wonderful if the native bacteria was able to clean up oil spills btw.


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## troy (Dec 2, 2014)

Add a little olive oil to watering? Lol..


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## gonewild (Dec 2, 2014)

Bjorn said:


> No problem with that, but why is the decomposed bark mix so detrimental? Sometimes it is and sometimes its not, but why?



Lack of air and space. 
And perhaps it is overloaded with a nutrient imbalance.


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## Brabantia (Dec 2, 2014)

Bjorn said:


> No problem with that, but why is the decomposed bark mix so detrimental? Sometimes it is and sometimes its not, but why?
> Wonderful if the native bacteria was able to clean up oil spills btw.


I would be pleased to know the pH of RO or rain water in contact with a decomposed bark.


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## naoki (Dec 2, 2014)

Rick said:


> That's a different conclusion from what I got (especially from fig 1).
> 
> -Moss with no plant or fert stayed at average of 5.0 su (after initial drop to ~ 4.0).
> -Moss with plant but 0 fert went from 5.0 to leveling off average of between 3.5 to 4.0
> ...



Oh, I see what you are getting. But the initial low pH with fertilization is due to the release of H+ (replaced by cations) which Bjorn explained in the first post. That's why pour-through measured after fertilization show much lower pH (pH 3.8 while fertilizer had pH 6) than the case where water was applied before pour-through. Pour-through was measured 30min after irrigation/fertigation. This initial drop in pH is indicative of high CEC. This is in the first paragraph of Discussion section.

Since we were talking about decay of media, I guess what the author (and I) tried to say is that decrease in pH over time is mainly due to roots (than accelerated decay of moss due to fertilization). In other words, I was talking about the change in pH over time. As you noticed, the change in pH over 30 weeks is small with only fertilization.

I do have the same question as Bjorn, why decayed media is bad (and Bjorn's idea is a possibility which I didn't think). Lance said lack of air. But is it really a issue if we reduce the watering frequency? Well if it is broken down to small size like Clay, then I can see that lack of air could be a problem. But maybe somewhat decayed media provide more stable environment (with regard to soil water potential/osmotic pressure).


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## troy (Dec 2, 2014)

Thank you brabantia


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## troy (Dec 2, 2014)

Can you get an acurate measure of media ph by collecting the ran through water or fertilizer mix from the bottom of the pot?


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## gonewild (Dec 2, 2014)

naoki said:


> Lance said lack of air. But is it really a issue if we reduce the watering frequency? Well if it is broken down to small size like Clay, then I can see that lack of air could be a problem. But maybe somewhat decayed media provide more stable environment (with regard to soil water potential/osmotic pressure).



It would be an issue if we reduce the watering frequency. When you have to reduce the watering frequency you are reducing what the plant needs to have to grow...water. In dead media that has no balance of living organisms to provide nutrients the plant relies on water to carry nutrient salts to its roots. If you have to reduce the frequency of watering because of the media condition then that condition is responsible for slower plant growth.

Somewhat decayed media would be a more stable environment. So the issue and challenge for a grower is to alter their watering and fertilizing based of the rate of decay of the media. Trying to do that sets up a route that can easily lead to disaster. That is why decaying media is bad, aside from the lack of air.


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## gonewild (Dec 2, 2014)

troy said:


> Can you get an acurate measure of media ph by collecting the ran through water or fertilizer mix from the bottom of the pot?



You can get an accurate "idea" what the pH is. But not as accurate as a lab result. The pour through method will give a very good idea about the pH the plant roots are subjected to.

What testing with the pour through method actually does is allow you to monitor changes in your media. Once you have a reading and then measure again at a future date you will see if the pH is remaining stable or changing. If it is changing a lot in a bad direction you can make cultural changes to correct the pH. This can help prevent bad problems. The same is true measuring the ppm or ec of the pour through water. You may not be getting the exact accurate measurement but using the same instrument and methods each time does show you what is changing.


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## Bjorn (Dec 3, 2014)

Naoki, I see that you understand what I am after. When it comes to moisture etc. we all know that many plants, typically phrags but also some paphs are standing with their roots more or less into flowing water or more common, water seepage. So moisture/wetness is not the problem. Most likely the main problem is the availability of oxygen dissolved in the water, and of course if the "mud" is caused by bacteria consuming available oxygen, then your roots will suffer. Of course, such an environment may be typical for most broken down mixes and if oxygen is not alloewd in the pot, well, then the roots perish. In such a case it might perhaps be a better option to increaser watering frequency in order to refill with fresh, oxygenated water.


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## Brabantia (Dec 3, 2014)

Bjorn said:


> Naoki, I see that you understand what I am after. When it comes to moisture etc. we all know that many plants, typically phrags but also some paphs are standing with their roots more or less into flowing water or more common, water seepage. So moisture/wetness is not the problem. Most likely the main problem is the availability of oxygen dissolved in the water, and of course if the "mud" is caused by bacteria consuming available oxygen, then your roots will suffer. Of course, such an environment may be typical for most broken down mixes and if oxygen is not alloewd in the pot, well, then the roots perish. In such a case it might perhaps be a better option to increaser watering frequency in order to refill with fresh, oxygenated water.


Bjorn, you cannot increase your watering frequency because a decaying substrate take a longer time to becomes dry. If you increase the frequency the substrate becomes soggy and the air circulation chances in the substrate becomes null.


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## Bjorn (Dec 3, 2014)

I know, and that is why eg baskets work. I water a lot and the compost is soaking wet for many species. No problem with decaying roots so far. But then, I normally use a lot of inorganic pebbles, sand, and other stone-based aggregates in the mix.
Xavier has written about dissolved gases and watering somewhere and he advised to aerate during hot summer particularly by spraying from above. 
I have my water in a big tank and heat to perhaps 22degrees. But additional to that I aerate with an aquarium type aereater (stone) from an ozone generator. But I do not think that the ozonegenerator works so its a simple pump probably.

A common problem is of course that people believe that paph roots must dry up. That is not generally true, look at the precipitation data from some of the places e.g. the polyanthas come from, its soaking wet all year.
Others, like many parvis have some drought during winter, but the region has lots of dew during night so perhaps its not that bone dry after all.
Back to start, my point was originally that by adding low amounts of fertiliser and relatively high amounts of calcium, the longevity of the substrate could be increased. All the rest is just to explain why this could be so.


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## Brabantia (Dec 3, 2014)

This is not the first time that I have the feeling that a substrate with a high content in mineral material is a good solution to solve problems linked with the decaying of the substrate and your mode of culture confirms this. Problems for me to test this solution is availability of a good inert material.


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## Bjorn (Dec 3, 2014)

Well, my assumption is that low fertiliser in every watering with relative high Ca to K is good for the logivety of the compost, -or the roots actually.


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## Brabantia (Dec 3, 2014)

Bjorn said:


> Well, my assumption is that low fertiliser in every watering with relative high Ca to K is good for the logivety of the compost, -or the roots actually.


This what I use and see my table #23 this thread.


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## troy (Dec 3, 2014)

Thank you guys for the helpfull info!!!


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## naoki (Dec 3, 2014)

Bjorn said:


> Most likely the main problem is the availability of oxygen dissolved in the water, and of course if the "mud" is caused by bacteria consuming available oxygen, then your roots will suffer. Of course, such an environment may be typical for most broken down mixes and if oxygen is not alloewd in the pot, well, then the roots perish. In such a case it might perhaps be a better option to increaser watering frequency in order to refill with fresh, oxygenated water.



Lance, both watering frequency AND how long it takes to dry out influence the water (and nutrient) availability to root (I'm sure that this is obvious and you tried to simplify this). If the media is moist for a longer time, they can get nutrient/water longer. The stable moisture level is considered to be one of the reasons why addition of 30% peat to bark-based media caused faster growths in Phal trials (e.g. Wang 1995. Medium and fertilization affect performance of potted Dendrobium and Phalaenopsis HortTechnology 5(3): 234-237). The bark only media dries quickly, so they did water twice as much as the pot with peat.

But higher frequency of watering might result in more oxygen as Bjorn said. Do you really think oxygenated water makes difference, though? The amount of O2 water can hold is tiny (around 10mg/l). In broken down media (or potting soil), top-watering is supposed to help exchanging the air in the pot. But it's a bit hard to imagine that it is a problem in pretty coarse orchid media. Soil respiration is an interesting point, too. I wonder how much this soil respiration contribute to the O2 level inside of the pot.

I briefly looked for an O2 probe to measure soil O2 content. I couldn't find a cheap one, but it would be fun to test how different watering is influencing the O2 level in the pot. Here is one from Apogee for $300. But it's a bit too pricey for me.


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## gonewild (Dec 3, 2014)

naoki said:


> Lance, both watering frequency AND how long it takes to dry out influence the water (and nutrient) availability to root (I'm sure that this is obvious and you tried to simplify this).



Yes that is correct I tried to simplify just to illustrate.



> But higher frequency of watering might result in more oxygen as Bjorn said. Do you really think oxygenated water makes difference, though?



It might. Not so much for bringing O2 to the roots but rather keeping the media atmosphere fresh for the micro organisms. Since we really don't know what organisms exist in the media associated with orchid and nutrition giving aerated water more closely mimics nature.



> The amount of O2 water can hold is tiny (around 10mg/l). In broken down media (or potting soil), top-watering is supposed to help exchanging the air in the pot. But it's a bit hard to imagine that it is a problem in pretty coarse orchid media. Soil respiration is an interesting point, too. I wonder how much this soil respiration contribute to the O2 level inside of the pot.



In coarse media the O2 should be good supplied from the atmosphere. It is in dense heavy medias that it may make a difference. It does make a difference where people have pots standing in wanter or roots submerged. Circulating the water is much better than still stagnant water. the circulation would mainly only be adding O2.



> I briefly looked for an O2 probe to measure soil O2 content. I couldn't find a cheap one, but it would be fun to test how different watering is influencing the O2 level in the pot. Here is one from Apogee for $300. But it's a bit too pricey for me.



Cheaper to just aerate the water!


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## Stone (Dec 3, 2014)

naoki said:


> > Do you really think oxygenated water makes difference, though?
> 
> 
> 
> Hydroponic people looked at this and found adding O2 to the water increased yeild in some crops but not in others.


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## Bjorn (Dec 4, 2014)

Naoki, just for fun, I re-calculated the amount of oxygen in water into volume gas STP (STP= standard Temperature and Pressure, i.e., 25 (20?)C and 1BAR) and it is really quite low; around 7ml/l; Or expressed as air: 33ml/l. But its there and actually not insignificant amounts either.

I originally started that aerating to disinfect my water with ozone. Additionally the rain in the tropics have been found to contain quite a bit of ozone during thunderstorms, so I thought that it could not be bad? I have used it for the last 5 years or so and can frankly not say that it has done much in a positive or negative way. 

BUT when that is said, because my source-water is reductive, by that I mean it sometimes smell sulphur (hydrogen-sulfide) it is improved by microbial oxidation in my tank and to perform well, that process needs some oxygen as well.

The reason for the reductive smell of the Source-water is that although I utilise rain-water, I have to top it with water from a nearby bog. You know the home of sphagnum etc? This water is relatively pure and contains little salts, and is quite neutral, but there is some sulphur in it causing it to smell slightly. Most likely, the bog-water contains most of the nutrients my orchids need, perhaps I should stop feeding? No, I do not believe it contains all the necessary elements. It does contain sulphur, which btw. should not be forgotten in the make-up of the fertiliser, right Mike?


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## naoki (Dec 4, 2014)

It is cheaper, but don't we want to know the truth, Lance?

Mike, that's interesting. I guess if it is a continuous system (roots are under the water all the time), it probably makes a difference. I wonder if oxygenation is beneficial with ebb-and-flow type.

Bjorn, I guess whether it is significant amount or not depends on the type of media (I forgot the correct words; water holding capacity and porosity??). It can be significant with high water holding capacity with small amount of air space. But if there is lots of air space then air with 200ml/l may dominate as the source of O2.

How do you carry bog water? Do you have a pickup truck with a big water tank (lots of alaskans have to carry their drinking water like this)?


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## Bjorn (Dec 4, 2014)

naoki said:


> Bjorn, I guess whether it is significant amount or not depends on the type of media (I forgot the correct words; water holding capacity and porosity??). It can be significant with high water holding capacity with small amount of air space. But if there is lots of air space then air with 200ml/l may dominate as the source of O2.
> 
> How do you carry bog water? Do you have a pickup truck with a big water tank (lots of alaskans have to carry their drinking water like this)?



Its some 30meters from the green-house Pump and some PE-tubing takes care of the transport. I am the proud owner of some Norwegian bog and that why I have toads in my greenhouse. Each year the tadpoles transform to tiny toads and frogs and crawl all around in the garden. This year it was so plentyful that you had to watch your step in order not to kill too many. Lasts only a few days, they disperse into the surrounding woods eventually.


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## Rick (Dec 4, 2014)

naoki said:


> Oh, I see what you are getting. But the initial low pH with fertilization is due to the release of H+ (replaced by cations) which Bjorn explained in the first post. That's why pour-through measured after fertilization show much lower pH (pH 3.8 while fertilizer had pH 6) than the case where water was applied before pour-through. Pour-through was measured 30min after irrigation/fertigation.  This initial drop in pH is indicative of high CEC. This is in the first paragraph of Discussion section.



Whether by H+ exchange or bacterial action. The scary part was that the incoming pH of the fert was adjusted up to 6.0 with NaOH and the media pH is shown to have pH of 3.8 almost instantly.

So the practice of raising pH of fert to compensate for substrate acidification seems to be pretty worthless.

Also if this is strictly a chemical CEC effect then you are doomed to never elevating pH with any base (Na, Ca, K, Mg OH) because you are saying that every cation going in is going to release H+ and run the pH down below that for neutraizing the incoming OH


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## Bjorn (Dec 4, 2014)

Another reason why low CEC substrates are better! Joke aside, remember that the number of sites is finite and they will get consumed and even if new ones are produced by the break-down of the substrate, its not impossible to handle. If you add alkalinity for instance, the reaction between the acid and the hydrogencarbonate wil make the carbonate decompose and evaporate as carbon dioxide. That way, having hard water with some alkalinity may be beneficial for your growing.
I do not have alkalinity in my water, so my approach is to reduce the CEC by not using sphagnum nor charcoal.


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## Rick (Dec 4, 2014)

gonewild said:


> Lack of air and space.
> And perhaps it is overloaded with a nutrient imbalance.



and you could add increase in pathogenic species of bacteria and fungus.

If you have conditions suitable for bacterial decomposition then there's a good chance once they are done with the bark they make the concerted attack on the living.


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## Erythrone (Dec 4, 2014)

Rick, are you sure bacteria and fungii able to decompose bark are harmfull to orchids ? I always thought wood decying organisms were unable to attack living roots of herbaceus plants.


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## Brabantia (Dec 4, 2014)

Bjorn said:


> Another reason why low CEC substrates are better! Joke aside, remember that the number of sites is finite and they will get consumed and even if new ones are produced by the break-down of the substrate, its not impossible to handle. If you add alkalinity for instance, the reaction between the acid and the hydrogencarbonate wil make the carbonate decompose and evaporate as carbon dioxide. That way, having hard water with some alkalinity may be beneficial for your growing.
> I do not have alkalinity in my water, so my approach is to reduce the CEC by not using sphagnum nor charcoal.


 A more mineral substrate then ... little by little we get there!


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## Stone (Dec 4, 2014)

Rick said:


> and you could add increase in pathogenic species of bacteria and fungus.
> 
> 
> 
> ...


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## Erythrone (Dec 4, 2014)

Stone said:


> No chance of that at all. Completely different species.



I agree


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## Rick (Dec 4, 2014)

Erythrone said:


> I agree



You think the same species of microflora living in cesspool are the same as the species living in a mountain trout stream?


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## Rick (Dec 4, 2014)

Bjorn said:


> The microbes have a part in this picture as well, but they are just consuming nutrients and producing colloids and what else they produce.



Actually nitrifying bacteria don't "consume" ammonia, but convert it from ammonia to nitrate (in a 2 species 2 step process) liberating H+ in the process.

This is a very fast process which makes all municipal waste water treatment systems (and your home aquarium) work.

This process has been well documented in agricultural systems when higher percentage ammonia and urea feeds are utilized.

http://www.upc.edu/growingmediacomp...growingmediacomposting2011.ISHS/s4-8-restrepo

But check out the above presentation. A bacterial nitrification inhibitor was added to stop the conversion of ammonia to nitrate (seemingly to get more ammonia into the plants). However, plant N uptake was already maxed out so instead of blowing nitrate out of the pots they leached out straight ammonia.


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## Bjorn (Dec 5, 2014)

From where did the nitrifyers come? What if you fertilise with K-liter only?
A nice presentation of the effect of nitrification inhibitor on the nitrification of urea in soil and coconut fibers.
1) these mixes probably have a retention time way above the potting mixes we use,
2) Isn't introducing nitrate vs urea a side-track? Unless the bacteria in question causes rot?
3) generally; if we tried to find results on monocots.. (but in this case I think its ok)


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## myxodex (Dec 6, 2014)

I've had pot acidification problems as well. I live in a hard water area (HCO3 =264 ppm; Ca ~ 120 ppm). I use sphagnum moss in my medium. I used to pre-soak the sphag in the rain water I use to water with, but then I changed this to 3 changes of straight tap water for half an hour each, squeezing out the excess water after each change. The water from the first change shows a drop in pH, but not so much afterwards.
I also add 5% tap water to my fert mix and my pH says above pH 5.


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## Rick (Dec 6, 2014)

Bjorn said:


> From where did the nitrifyers come? What if you fertilise with K-liter only?
> A nice presentation of the effect of nitrification inhibitor on the nitrification of urea in soil and coconut fibers.
> 1) these mixes probably have a retention time way above the potting mixes we use,
> 2) Isn't introducing nitrate vs urea a side-track? Unless the bacteria in question causes rot?
> 3) generally; if we tried to find results on monocots.. (but in this case I think its ok)



Nitrifiers are ubiquitous in soils and aquatic systems. They probably are on your hands when after you handle the bathroom door knoboke:

The residency time is short. Under aquarium applications with a trickle filter running on a tank with a 6X volume/hour turnover rate (or industrial/municipal waste treatment plant) the contact time with the biological media is on the order of minutes to get complete conversion from ammonia to nitrate. De-nitrification (from nitrate to N2 gas) is usually a little slower, and needs carbon input.

Note in the rose pot example that two levels of biological activity are occurring.
1) Urea is split into ammonia by bacteria
2) ammonia is converted to nitrate.

The conversion from ammonia to nitrate is actually a 2 step process using 2 species of bacteria living in spherical colonies. So in the pots stopping nitrification they should have measured nitrites in leachates to see which stay is effected more and do a more complete mass balance of N going through the pots.

Also note that plant parameters (including N in leaf tissue) were not significantly improved with more urea getting stuck as ammonia.

There is a full paper of this presentation on the internet, but I can't find it for free. From reading the free abstract there was also mention of pH changes.

Bottom line is that the plants took up almost nothing. What went into the pot (whether going in as urea or ammonia) most of it leaves the pot un-utilized by the plant as nitrate via bacterial activity.


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## Rick (Dec 6, 2014)

Bjorn said:


> A nice presentation of the effect of nitrification inhibitor on the nitrification of urea in soil and coconut fibers.



Not sure how much of this experiment was conducted in "soil".

The alternate media to coconut fiber was "burnt rice husks".

And one of the slide points was on growing in soil-less media. 

Maybe in the full paper is there more detail of soil systems.?


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## Rick (Dec 6, 2014)

Also the above look at aqueous leachates only looks at the aerobic side of pot microbiology.

Since the anaerobic side is taking nitrates to N2 gas (nitrous oxide if conditions are not efficient) you would need to sample the gas above the pots to complete the mass balance calculations for what happens to N going into pots.


http://naldc.nal.usda.gov/naldc/download.xhtml?id=54341&content=PDF

This paper does show significant nitrous oxide burping out of pots with fertilizer application.


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