# Optimal acidity of Paphios fertilyser solution



## Brabantia (Aug 23, 2011)

In relation to what Rick said about Calcium assimilation (thwarted by a potassium excess) I wonder which is the optimal pH to fertilize the Paphios. A pH from 6.8 to 7 is usually recommended on this forum. I now have just read this on the FLORICULTURA (Holland) site: "When the pH values of water exiting the reservoir and containing nutrients exceed 6.2, sulphates and phosphates react with calcium ions and are no longer accessible to plants". 
Which is the opinion of the specialists on this subject? Many thanks in advance.


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## SlipperKing (Aug 23, 2011)

Keep the pH a round 7.0


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## poozcard (Aug 23, 2011)

for me i keep it higher than 7


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## likespaphs (Aug 23, 2011)

graphical listing of availability of soil nutrients by pH. don't know how orchid media....
http://web1.msue.msu.edu/monroe/soilweb2/availability.pdf


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## Brabantia (Aug 24, 2011)

Thank you all for your responses. But, simply a remark: The MSU table shows the solubility of each cation taken individually according to the pH, but not the solubility (and thus the availability of the cations, Ca++ as for example) in the presence of sulphate or of phosphate according to the pH.


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## Ray (Aug 24, 2011)

1) As was stated, that "availability" chart (a very old one, from a single test of a single fertilizer and a single soil, and only demonstrates solubility, according to Bill Argo, the "MSU Fertilizer" guy) is of little to no value to orchid growers. It's not worth much to any grower actually, as different starting fertilizer raw materials and different soil ingredients can all affect "availability".

2) It seems to me that if the ion is in solution, it is likely available for uptake by the plant. If it is complexed in any way that makes the molecule big enough to prevent uptake, I'd think it would precipitate.


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## eggshells (Aug 24, 2011)

Is it okay to have a slightly acidic water, let's say ph 6 and have dolomitic lime as top dress or mix in the medium? Will this slightly increase the ph when you water?


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## Paul (Aug 24, 2011)

I would say 6.5 is a good value, for good assimilation of most nutrients. But, to avoid iron excess for some sensitive species, is seems to be better to be close to 7 (what I do, about 7 with my water and neutral fertiliser similar to MSU)


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## Justin (Aug 24, 2011)

i adjust my fert solution pH to around 7


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## terryros (Aug 24, 2011)

It is not just your fertigation water that matters but what your growing media does or doesn't do to chemical composition. I now do a pour-through of about 50 mL of RO water, usually within a few hours of watering, and collect the effluent. I then measure the electrical conductivity and pH of the effluent. My review of published literature suggests that the effluent should not get over about 1 mS/dL (ppm will vary with different meters). pH optimums seem to vary not just by orchid genera but by species within a genera. I grow in pure sphagnum and try and keep pH of the effluent between 6 and 7 for most all plants. I use as needed top dressing with dolomitic lime (containing both calcium and magnesium carbonates) to keep the pH up.


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## Brabantia (Aug 25, 2011)

I note that this subject is rather hot considering the interest developed by who intervened , I thank you. But I would like that the discussions will be a little more refocused on the calcium - magnesium assimilation at hight pH (6.5 to 7 and higher), as it seems to me values usually used by the majority of Paphs growers specialists.


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## SlipperKing (Aug 25, 2011)

I'm not sure I can answer you completely because I haven't check the pH in awhile but here it goes. I'm feeding ~100 ppm of N, ~7 ppm of P, and ~8 ppm of K that is the straight fertilizer. Then I add dolomite (palletized) lime which is made up of Ca and Mg at ~30 ppm of Ca and whatever the Mg comes out to. I figure there is plenty of PO4 in the lime to make up for any short coming in the Fert. 
All I can go by is the plants as for how well things are going. Not to brag too much but everything growing at a very good pace. Nothing has stopped growing like in past years. That is one thing years ago speakers at our meetings would bring up about summer heat. They always recommended stopping fertilizing when the temps get into the 90's because the physiology of the plants would slow way down or stop all together. I do not see this at all now that I understand more about nutritional requirements of these plants. I have also taken note of very little to none-rot problems. No summer bud blasts I use to get (of course there's not much trying to open at the moment). I do have a number of buds forming, same plants as in the past.
I'm using rain water and with the nutrients I'm adding it got to be pretty close to neutral pH.


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## Paul (Aug 26, 2011)

In my memory: Magneisum is best assimilated at high pH (7-7,5)


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## Brabantia (Aug 26, 2011)

@ Slipperking: Dolomie is a Calcium/Magnesium carbonate mix, no phosphate in it.
@ Paul: at pH 7 and higher magnesium is in the form of magnesium hydroxide - its solubility is 12 mg/L. The Mg++ content is very low.

The only way to maintain Ca + + and Mg + + in solution (available for the plant) at high pH is to introduce them in the form of chelates (complex).


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## Ray (Aug 26, 2011)

I know the charge on the cation can affect assimilation by the plant, but once assimilated, does it matter, or will it be converted to whatever is "right"?


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## Rick (Aug 28, 2011)

There's a good chart on optimal assimilation pH on the ANTEC orchids reading room site. http://www.ladyslipper.com/minnut.htm For most nutrients it tends to run to mild acidic 5.5 to 6.5 s.u. This pH range is fairly universal for terrestrial and freshwater plants. Even in ecosystems where the geology may produce higher pH values the bacteria/fungi in the rhyzosphere will modify the pH around the roots to accommodate this range. 

pH of the fert mix is somewhat irrelevant for pass through feeding (as opposed to SH or full hydroponic systems) since the contact time is short and the pH is modified by the potting mix very quickly.

I used to pay a lot of attention to fertilizer pH but quit a few years ago. Maintaining some level of buffer in the potting mix to keep from getting chronically too acid (below 5.5) is important, but I wouldn't try to push it up beyond 7.5.

My P. rothshchildianum, and P stonei have never grown better since going into baskets of sphagnum (with some sand, limestone gravel, and some aragonite sand). And these are species coming from either ultra-basic serpentine or limestone cliffs. I've collected drainage water out of the bottom of the baskets and it has a pH of 6.0 - 6.5 s.u.


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## Rick (Aug 28, 2011)

Paul said:


> In my memory: Magneisum is best assimilated at high pH (7-7,5)



Remember pH goes from 0-14, and pH 7 is neutral (not high). 

Within 6.0 to 9.0 just about any aquatic organism will be just fine.


6.5 to 7.5 is almost always a safe bet for any horticultural project.


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## Carper (Aug 29, 2011)

I have been using RO for a couple of years now with the PH coming out at the neutral 7. Adding the MSU 13-3-15 at the recommended rate, which is about 600 Microsiemens strength, brings the PH automatically to 6.2. I have had very good growth, but have also added epsom salts/magnesium sulphate and recently liquid silicon. The liquid silicon I use to sometimes increase the PH if too low. I haven't had any adverse reaction from the plants but wondered if by increasing the PH, this would increase the uptake of the magnesium/calcium supplementation?

As you have stated Rick, I take it the feed modifies the PH quickly due to the short period when it is passed through the pot. Is this why when the feed is poured directly on the roots they burn and normally die, hence it's best to cover them as much as possible with the medium. 

Gary
UK


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## Rick (Aug 29, 2011)

Gary if you look at the chart near the bottom of the page from ANTEC you will see that the "optimal" uptake pH is VERY broad.

The point of "burning" roots by pH is even broader.

At this point playing around between 5.5 and 8.5 probably amounts to just a few percent difference that's not worth quibbling about.

Two years is still a short amount of time to see the calcium deficiencies I saw before cal/mag supplementation. Since you've been adding epsom salts you might be able to stretch it out for a couple more years before really noticing the wide range of issues I was seeing excess K in the system.

If you have a heavy dose of solid based Ca (like dolomite or oyster shell) in your potting mixes, and curtail feeding during winter, you may never experience a K related Ca deficiency. 

The first signs will probably be new growths are progressively smaller and flower faster than previous. And incidence of rots (especially Erwinia) will go up.


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## Rick (Aug 29, 2011)

Carper said:


> As you have stated Rick, I take it the feed modifies the PH quickly due to the short period when it is passed through the pot. Is this why when the feed is poured directly on the roots they burn and normally die, hence it's best to cover them as much as possible with the medium.



pH 5.5 to 8.5 should be acceptable for hydroponic systems where roots may be continuously exposed to these pH levels.

This range is still only weakly acidic and weakly basic and well within the normal range for soils and aquatic organisms.

Nobody "burns" in this pH range. Need to get to below 2 and greater than 11 to get to something close to burning. There is life at pH 4 and pH 10, but not very normal life. The pink ladyslipper (Cyp acule) and several other terrestrial orchids thrive at pH's around 4-5 s.u.


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## Rick (Aug 29, 2011)

Rick said:


> pH 5.5 to 8.5 should be acceptable for hydroponic systems where roots may be continuously exposed to these pH levels.



There may be a case to be made when using ammonia based fertilizers, that the higher pH of around 8.5 changes the ionic state of ammonia to a much more toxic state which is generally lethal to aquatic life (even nitrifying bacteria that "eat ammonia").

But a pH of 8.5 in and of itself is not toxic or corrosive to aquatic organisms.


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## Brabantia (Aug 30, 2011)

I do not think that this is a pH too high or too low, which is causing burns to the roots but the drying effect of the salts accumulated on it when the roots dry. I am always surprised when Ray B. calls 125 ppm nitrogen for growing orchids, but remember that he grows mainly in semi-hydroponic, the roots are always wet or damp at least. A few years ago I tried to grow my Paphios with 125 ppm nitrogen, growth was strong but the following year when I repotted it most of the roots were dead. So I lost my Paphio Ho Chi Minh and Paph. rothshildianum x kolopakingii and others. The limit seems to be for me around 50 to 60 ppm nitrogen once every 8-10 days, but in any case never exceed 600 µS of conductivity for the fertilizer solution.


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## Bjorn (Aug 30, 2011)

Never understood this ppm N story either. As a professional in chemistry, I cannot understand that the amount of N should be decisive here, the total ionic strength must be much more important. When that is said, it does give strong growth to many plants. On the reverse side special procedures have to be applied in many cases like flushing etc. Of course because the pots gets overloaded with salts. In nature, all (?) paphipedilums are growing on nutrition poor substrate. 
Since man has an affinity to size, we judge sucess by size and get temptet to put our plants on "steroids". Of course too much of the good is not good for you so additional to size we get all kinds of side-effects like rot etc. I think that Ricks ideas about potassium and calcium makes sense, as does Xaviers findings of Nitrogen from nitrate vs. ammonium. Personally, I have recently started a slight application of Urea as foliar feed, just to check.
I have for a while tried to find fertilisers low in potassium, but it seems to be difficult to find. Currently the procedure is to dilute the fertiliser - btw. I am using some 40ppm N - but that lowers the micronutrients.
Enough for now, perhaps this topic should have its own thread?oke:


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## Rick (Aug 30, 2011)

Brabantia said:


> I do not think that this is a pH too high or too low, which is causing burns to the roots but the drying effect of the salts accumulated on it when the roots dry. I am always surprised when Ray B. calls 125 ppm nitrogen for growing orchids, but remember that he grows mainly in semi-hydroponic, the roots are always wet or damp at least. A few years ago I tried to grow my Paphios with 125 ppm nitrogen, growth was strong but the following year when I repotted it most of the roots were dead. So I lost my Paphio Ho Chi Minh and Paph. rothshildianum x kolopakingii and others. The limit seems to be for me around 50 to 60 ppm nitrogen once every 8-10 days, but in any case never exceed 600 µS of conductivity for the fertilizer solution.



Keep in mind using a balanced fertilizer that if you had 125 ppm of N you also had 125 ppm of K , and little to no Ca and Mg to balance it.

The monovalent cation salts (K and Na) are real hard on plants if the divalent cations (Ca and Mg) are not in excess to balance. Since most tap waters have some calcium and magnesium in them (calculable from Hardness values), many orchid growers may not experience the worst of effects due to K overdose and antagonism compared to growers starting with RO water.


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## Brabantia (Aug 30, 2011)

This last discussion reminds me an article by Bob Hamilton in which he advocated that the best fertilizer for Odontoglossum growing have a composition near 3-1-2 (NPK ratio). This ratio corresponds to the one found by chemical analysis of plant tissues in general. I'm curious to see what such a fertilizer would give for results for growing paphios ... of course with some of the nitrogen supplied by calcium nitrate.
Ref: http://members.cox.net/lmlauman/osp/html/odontoglossums.html


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## Rick (Aug 30, 2011)

Brabantia said:


> This last discussion reminds me an article by Bob Hamilton in which he advocated that the best fertilizer for Odontoglossum growing have a composition near 3-1-2 (NPK ratio). This ratio corresponds to the one found by chemical analysis of plant tissues in general. I'm curious to see what such a fertilizer would give for results for growing paphios ... of course with some of the nitrogen supplied by calcium nitrate.
> Ref: http://members.cox.net/lmlauman/osp/html/odontoglossums.html



The problem I'm finding with some of these early analysis of "optimum" plant growth leaf analysis is that they were conducted on cultivated plants (which are already extra loaded in K). And also note that no mention of Ca and Mg is included in the discussion.

The data I have been digging up for plant leaf analysis is from jungle collected (insitu) plants, Including that for karst and ultrabasic (serpentine) based geology forests. I even have some data for tropical epiphytes (but still not specific to orchids). I've avoided data that did not include complete N P K Ca and Mg data. In general K is less than half, and maybe even 1/4 the N value. Ca is often twice the K value and Mg is usually equal to the K concentration. One document included silicon which came in at less than Ca but greater than K and Mg.

As I've been pointing out in other threads (and born out in more than one paper I've located), plants (especially tropical epiphytes) are very efficient at absorbing and sequestering K. K is relatively rare in the environment, so plants have active selection mechanisms to absorb and store K while other nutrients are absorb more passively (since they are more commonly available.

Subsequently any invitro leaf analysis data is generally biased to the type of fertilizer given to the study plants prior to analysis. Particularly with regard to K concentration. If the literature base is based on commercial crops, especially annual crops like corn and wheat, the K concentrations are very high. I have a paper on leaf tissue analysis of green house grown phalaenopsis which shows very high ratios of K, but the nutrient ratios of green house grown phals are nothing like the ratios of insitu tropical epiphytes.

Just like feed lot cattle, you can feed corn (which is not a natural diet for cows) and get short term superior growth rates, but they are dependent on antibiotics to keep from dying. How often have you heard of growers that insist that GH orchid management requires the use of all kinds of fungicides and pesticides for disease control? I have one paper that shows how the resistance of plants to bacterial and fungal diseases like botrytus and erwinia rots is drastically reduced as K leaf tissue concentration exceeds the Ca concentration.


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## SlipperKing (Aug 31, 2011)

Rick,
I thought this was very significant! 
" I have one paper that shows how the resistance of plants to bacterial and fungal diseases like Botrytis and Erminia rots is drastically *reduced *as K leaf tissue concentration exceeds the Ca concentration."


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## Paul (Aug 31, 2011)

SlipperKing said:


> Rick,
> I thought this was very significant!
> " I have one paper that shows how the resistance of plants to bacterial and fungal diseases like Botrytis and Erminia rots is drastically *reduced *as K leaf tissue concentration exceeds the Ca concentration."



very interesting note!!


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## Ray (Aug 31, 2011)

Brabantia said:


> I do not think that this is a pH too high or too low, which is causing burns to the roots but the drying effect of the salts accumulated on it when the roots dry. I am always surprised when Ray B. calls 125 ppm nitrogen for growing orchids, but remember that he grows mainly in semi-hydroponic, the roots are always wet or damp at least.


I'm not sure that it's a matter of the roots staying constantly wet, but more of the fact that my pots get thoroughly flushed at every single watering. The fact that the medium stays moist means there is less precipitation - actually, close to none where it does stay constantly wet, and only slight buildup on the parts that do dry out for a short time - so that does help, too.

Don't forget that my 125 ppm N recommendation is merely copied from the MSU study published in the AOS magazine, and found to be generally good. Incidentally, Bill Argo told me their selection of that level was derived the same way - they tried it, and it seemed to be a good level - period. No scientific derivation.


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## Brabantia (Aug 31, 2011)

Ray said:


> I'm not sure that it's a matter of the roots staying constantly wet, but more of the fact that my pots get thoroughly flushed at every single watering.



@Ray: when you write:"flushed at every single watering" it is with some fertilyser (enough to reach 125 ppm N) in your water?



> The fact that the medium stays moist means there is less precipitation - actually, close to none where it does stay constantly wet, and only slight buildup on the parts that do dry out for a short time - so that does help, too


.
We are over the same length of wave

@ Ray: A 125 ppm nitrogen fertilizer solution MSU has a conductivity of about 1000 µS. When growers uses a conventional substrate composed of bark, CHC,perlite...., unless they distribute this solution on previously wetted roots, it is a real risk of roots burns. Around 600 µS (approximately 60 ppm N with MSU) seems to be a maximum concentration to use without risk of roots burns in conventional substrate... remember the Anglo-Saxon adage: weakly weekly.
Ray, please correct me if I am wrong.


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## Brabantia (Sep 7, 2011)

As on CNN, No comments, Ray?


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## Ray (Sep 7, 2011)

Oops. Sorry.



Brabantia said:


> @Ray: when you write:"flushed at every single watering" it is with some fertilyser (enough to reach 125 ppm N) in your water?


Yep. Been doing that for years. I have not flushed with plain water (except maybe a time or two when I ran out of fertilizer concentrate in the tank) in over 15 years.



Brabantia said:


> @ Ray: A 125 ppm nitrogen fertilizer solution MSU has a conductivity of about 1000 µS. When growers uses a conventional substrate composed of bark, CHC,perlite...., unless they distribute this solution on previously wetted roots, it is a real risk of roots burns. Around 600 µS (approximately 60 ppm N with MSU) seems to be a maximum concentration to use without risk of roots burns in conventional substrate... remember the Anglo-Saxon adage: weakly weekly.
> Ray, please correct me if I am wrong.


I will not say you are "wrong", but my experience doesn't necessarily agree.

Not all of my plants are in s/h culture. I have a number of plants in Orchiata bark, some in sphagnum, some purchased in a typical bark/perlite/charcoal blend, some in EcoWeb chunks, some mounted, and some totally bare root in baskets, and they all get watered with the same solution at the same frequency, and I have never had a damage issue.


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## Brabantia (Sep 7, 2011)

Thank you all for this very interesting exchange of views on this "hot" subject.


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## gonewild (Sep 7, 2011)

I agree with Ray on the subject of nutrient solution on dry roots. I have never seen any adverse reaction either.

The main reason to water your plants with plain water before applying the fertilizer solution is to avoid wasting fertilizer. If your media is dry, it tends to shed water, and when you apply fertilizer solution to it a lot of the solution runs out the bottom of the pot before the media is saturated, and thus you just poured a lot of valuable nutrients on the floor. If the media is already wet then it only takes a small amount of nutrient solution to soak the media and reach the roots.

It may not make a big difference on a small collection but it could easily cut your fertilizer expense in half.


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