Optimal acidity of Paphios fertilyser solution

[Rick]

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.

 

[Brabantia]

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.

 

[Bjorn]

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:

 

[Rick]

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.

 

[Brabantia]

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

 

[Rick]

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.

 

[SlipperKing]

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."

 

[Paul]

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!!

 

[Ray]

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.

 

[Brabantia]

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.

 

[Brabantia]

As on CNN, No comments, Ray?

 

[Ray]

Oops. Sorry.

@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.

@ 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.

 

[Brabantia]

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

 

[gonewild]

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.