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