pH in S/H

[Ray]

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.

[Intruder]

Originally Posted by Ray

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.

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.

[Intruder]

Originally Posted by Intruder

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?

[Shawna]

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

[Ray]

Originally Posted by Intruder

No comments?

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.

[Jacaranda]

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.

[Jacaranda]

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

[orchids3]

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.

[Jacaranda]

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.

[orchids3]

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?