Optimal acidity of Paphios fertilyser solution

[Brabantia]

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.

 

[SlipperKing]

Keep the pH a round 7.0

 

[poozcard]

for me i keep it higher than 7

 

[likespaphs]

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

 

[Brabantia]

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.

 

[Ray]

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.

 

[eggshells]

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?

 

[Paul]

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)

 

[Justin]

i adjust my fert solution pH to around 7

 

[terryros]

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.

 

[Brabantia]

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.

 

[SlipperKing]

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.

 

[Paul]

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

 

[Brabantia]

@ 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).

 

[Ray]

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"?

 

[Rick]

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.

 

[Rick]

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.

 

[Carper]

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

 

[Rick]

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.

 

[Rick]

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.