pH in S/H
 

I am starting garden plants in S/H and will be setting up a true hydro system soon. The hydro sites all talk about the importance of maintaining a slightly acidic wetting solution to improve nutrient uptake and to eliminate salt adhesion to the clay media. This might help explain some of the recent complaints about Prime Agra in another thread. I have searched, but have not found any discussions about lowering pH for S/H.

There are tons of good info sites, but here is start:

Simply Hydroponics - pH

And an exerpt:

WHY IS pH IMPORTANT?

When the pH is not at the proper level the plant will lose it's ability to absorb some of the essential elements required for healthy growth. For all plants there is a particular pH level that will produce optimum results. This pH level will vary from plant to plant, but in general most plants prefer a slightly acid growing environment (between 6.0 - 6.5), although most plants can still survive in an environment with a pH of between 5.0 and 7.5.

When pH raises above 6.5 some of the nutrients and micro-nutrients begin to precipitate out of solution and can stick to the walls of the reservoir and growing chambers. For example: Iron will be about half precipitated at the pH level of 7.3 and at about 8.0 there is virtually no iron left in solution at all. In order for your plants to use the nutrients they must be dissolved in the solution. Once the nutrients have precipitated out of solution your plants can no longer absorb them and will suffer (or die). Some nutrients will precipitate out of solution when the pH drops also.

From orchidusa.com: The Leading Orchids Site on the Net

Influence of PH on nutrient availability.

So far we discussed fertilizers, the proper dosage of fertilizers and proper watering, but giving the proper fertilizer in the proper dosage is only part of the issue. We need to make sure the nutrients are made available for the plants to use.
Nutrient availability to plants is affected by PH levels. See chart on page 15 of “An introduction to Orchids” published by the South Florida Orchid Society.
As an example, Phosphorous is practically not available to plants in the PH range of 7.0 to 8.5. Availability of the trace element Manganese is mostly available between a PH level of 4.0 to 5.5. Boron between a level PH of 4.5 to 6.0.
The above mentioned chart (produced by Michigan State University) shows that most nutrients are available at their optimal level between a PH level of 5.0 to 6.0.

An article in the fall 1997 issue of Greenhouse Grower, although not about orchids, states: “When the PH of the media is too high, micronutrient deficiencies can be a problem. If the PH is too low, micronutrients become more available and can lead to micronutrients toxicity in some crops.”

Even if we started with water with an acceptable PH, the PH will change, up or down, depending on the additives (fertilizer, root solution, ....) we used. So, after we added all additives, we must adjust our PH to a level that will make these nutrients and other additives available for the plants to use.
Most orchid sources recommend a PH between 5.5 and 6.5 for orchids and that’s what we aim at after adding nutrients and / or other additives

I haven't taken the time to actually test things out, but I'm pretty sure Ray has done some extensive experimenting with pH. I can't find the article right now, but I know he posted something on the internets about it. :scratchhead:

The conclusion was that you should always use dilute fertilizer (approx 125 ppm) and that the rest would sort itself out ok.

There is some information on Ray's site regarding pH and nutirent availability - recommended is 6.5-6.9. I myself have never tested my fertilizing solutions. :shock:

Fertilizers & Plant Nutrition

Actually this reference on Ray's site recommends 5.8-6.2 for orchids.

Plant Nutrition

Tested my supply water and watering solution tonight with a calibrated pH meter. Here are my results.

Supply water - pH 7.1
I use carbon filtered water (not RO).

Watering/Ferilizing Solution - pH 6.8
1 gallon supply water
1/4 tsp Superthrive
1/4 tsp MSU fertilizer (tapwater formulation)

After adding 1/4 tsp "pH Down" from local hydroponics store the pH dropped to 5.9

That chart that shows nutrient availability may not have as much validity as we think.

I have spoken to some MSU folks, and the comment was that it was a measure of the solubility of one brand of fertilizer is one blend of potting soil, but it has been erroneously used as the "gospel" on pH and "nutrient availability".

As far as I am aware, the LECA media on the market do not interact with the nutrients to affect the pH in any way, and I'm pretty sure the pots are the same.

The MSU fertilizer for RO - and the other "pure water" formulas available - will buffer the pH when put into solution. For users of mineral-bearing water supplies, it's pretty well buffered right from the tap.

That's not to say it doesn't change in-use, as the plants' processes do affect the chemistry.

Could anyone recommend a reasonably priced pH meter that works?

I would suggest you buy Ph paper... you need to choose the righ scale you want to work with... A great price value balance and perfectly suitable for most of the goals you normally want to achieve... Especially, if you are going to use it only once n a while...

unless you are really going into "high-tech" lab work, then you do need a good Ph-meter

By the way, after doing more research, I have reevaluated my pH range recommendation for most orchids to be in the 5.5-6.5 range, with somewhat higher also being acceptable.

Some paphs prefer a higher level - low to mid 7's - although I must say that mine are doing well with a constant 5.8.

Noe, et al - I have a good pH and EC meter, so if you want to send me a sample, I'll be happy to test them for you. Make it about a baby food jar volume at a minimum, and run the water for a while before filling it, and make sure the container is very clean and well-rinsed first.

It seems to me (and I have read this several times) what is important is not the pH of the fertilyser solution but the pH of a lexiviate as for example two days after a fertilyser distribution.

No comments?

Sailor,
Do you know what the ph would be without super thrive added to it? My Tap Water is 7.1 also.

OK, a comment.

Plants affect the environment around them in several ways:

1. They absorb nutrients from the solution.
2. They expel "counter-balancing" ions when they do.
3. The also have metabolic processes that result in waste products.

Add to that the fact that a solution will react with the atmosphere around it.

So what conclusions will you make from a pH a couple days after watering?

Orchid media have little- to no "cation exchange capacity", so don't really react with any of the above. That means that your solution is the mitigating factor. That is, water to return things to the "target" chemistry.

For many years I asked the question - how do epiphytic orchids get their nutrition, in the wild, and how much do they get ,( and pH is part of that question). I never got a satisfactory answer, and I went to a lot of lectures by experts of all kinds over many years. Then I had the bright idea of gfoing to see for myself . I went to a rain forest where I could see epiphytic orchids, and I went in the rainy season. I collected rain from a clear sky, and from that trickling off the aerial roots of some dendrobiums ; ditto off the leaves of paphs ( for example). My results have been published in several journals around the world over the years since I did that - the latest one being the Dutch "Orchideeen" Number 5/2010. But to summarise, they get nutrition at about 600 mS ( 0.6 Siemens EC) and at pH6.0. What they get is more or less what is in greenplant sap, diluted by rain-water - because thats where it comes from - the exudates which are in effect pumped out of the leaves of the trees, vines etc, on which the orchids cling.

p.s. And ever since then I have used those figures , as a general rule, on all orchids, at every watering....

pH of 6.5 to 7 works great for me. If you will top dress with a mix of Granular Dolomite Lime 1:1 and Crushed Sea Shell the media I use maintains that almost automatically. The seashell/lime acts as a buffer and only releases when the mix goes acid (Calcium is released). Both are Calcium Carbonates.
When pH is 7 or above the buffer does nothing. You would need a pH downer. Have had a good pH meter or two and although accurate they are a bit of a pain to use due to the constant need to calibrate the things. Also they dont last very long. A good aquarium pH test kit will get you close enough for plants. Somewhere I have a chart which I understand was prepared by the California Dept of Agriculture and was in one of Bob Gordons books. will try to find it and post it. Was a presentation of the most effecient pH for each nutrient to be taken up by the plant. Media breakdown is one of the things that will lower PH. How do people who use organic media know that is is the water fertilizer which is lowering pH not rotten media? believe its the pH inside the pot which is most important - not necessarily what you put in at the top.

Here is another chart ; this one came from Australia and a firm specialising in supplying nutrients for commercial tomato growing in hydroponics ; but all green plants have great deal in common - this chart is one I used in lectures on hydroponics for orchids in England in the 1990s and it was published on my personal web-site which I ran from the late 1990s until maybe 2005.

Jacaranda,
Your chart shows the same information and agrees with the chart I remember. My cymbidiums and slippers are kept at a pH of 6.8 to 7.2. most of the others are arond 6.5. The Paphs, Phrag and cymbidiums get the heaver dose of lime/ seashell mix as per my previous post. With the exception of Iron - the nutrient uptake is as good in the higher range - up to 7.2 as the lower range in the "green Zone". Have attended lectures that indicate that a lot of Cattleyas require almost toxic levels of Iron to do well. Maybe some plants need to be in the range where more iron is available - hence lower pH requiremnts. My Cyms seem to like the Potassium range hence my higher range. Could it be that the plants would do better if I shifted pH at differant times of the year? Like the rainy season in the Himalayas more acid (lower pH) hence more nitrogen (spring and summer) or drier - higher pH -more in the Potassium range because what water there is exposed to the calcious rock in the area. Maybe it depends on where the plants grow in nature?

Sorry, Jacaranda - that's the same BS chart I was referring to earlier.

Something like that gets published, and over time, nobody knows the where the data came from or the details behind it, so it becomes "gospel".

I did tell you !
 

I did say where I got the chart from !.

It is a good chart in my opinion - but orchids are adaptable and they can make some adjustment in their own roots. So I would take away the green zone. My stage of chasing pH has ended to the point that I only rarely check it anymore. If I make fertilizer brand changes or media changes then I check. It is also a good check for media breakdown if you measure what comes out of the pot not what goes in. What I have observes is that roots rot more at lower pH (acid ) and much less at neutral (pH 7). Am using rocks (Stalite) so media breakdown is not a consideration.

I don't know exactly when the experiment was done that led to the generation of that chart, but it was based upon a single experiment with a single soil sample.

The availability of nutrients in soil is directly related to its cation exchange capacity, and CEC is definitely related to pH. But we don't grow in soil, and the CEC of most orchid media is essentially zero.

The fact that the graph has been used by "experts" for years - heck, I treated it as gospel until I learned better - does not mean it is valid and/or pertinent.

Sorry buys, but my own opinion is that there's WAAAAY too much worry about pH.

Very dilute solutions have little buffering and can vary wildly with slight changes. Even shaking a sample will dissolve more CO2 (which forms carbonic acid) and drop the pH. My own feeling is that in well aerated media this natural gas exchange will keep the pH the orchid sees in a good range.

Unless you live in an area with very hard and/or alkaline water, worrying about pH is probably more effort and the energy could better be spent repotting something, checking for pests, etc..