Do you adjust pH when watering?

[goodgollymissmolly]

Steven, I hear what you are saying and I have considered the same thing myself.

Problem is that you are postulating an idea to support the widely held "need 6" theory. I have no issue with the "need 6" for terrestial plants because it's supported with the chemistry of what plants need and how it can be best delivered. I see no data that says this "6" is available to orchids in a tree.

I am not saying the "need 6" is wrong. I am simply questioning how it works and how the rainwater in a tree gets to be 6. Surely some intrepid orchid explorer has measured the pH of the water in an orchid tree. For goodness sakes they have measured the value of everything else to the nearest RCH.

Unfortunately, I find many ideas about growing plants to be urban legends passed down from great grandmother. Is this one of them? I simply do not know and am asking if anyone else knows.

[IdahoOrchid]

Measure the PH of some rain water. Put some sphag moss or any other moss along with some other things that might be found in and around the roots of an orchid growing in a tree in that rain water. It would not take much and probably would be best to be a small amount.

Measure the PH over a period of hours, maybe 24 and up to 48, and see what happens to it. Do you think the PH will decrease do to the contact with the material?

[goodgollymissmolly]

I just don't know what would happen, Steven. I did measure my rainwater at 6.9. First I do not think there is any sphag moss in the trees with orchids. I'm pretty sure that the effect of various items in the water might be different depending on what it is. I mean what does poison ivy do to water...probably nothing but I don't know. As we say in engineering...I bring no data just closely held misconceptions from childhood. Absolutely, I think rotting vegetation in the water would make it acid.

I do not visualize the water in a tree to be a puddle of rotting vegetation. I see it as a flow of relatively pure water existing during a rain and shortly thereafter. Certainly it dissolves some stuff and wets the bark.

I guess I do not understand why you choose to dream up theories rather than joining me in asking for actual in situ data. Both of us can guessimate what happens til hell freezes over, but doesn't someone actually know from measured data?

[flhiker]

I don't know and don't pretend to be a expert at anything!! But could I be of some help by checking the ph on the trees that have orchid growth and the water that flows in the Everglades? I do plan on a hike in the glades within the next two weeks. Any suggestions on how I might collect such data? Or is this just a waist of time?

[Ray]

1) There have been chemical analyses of "forest canopy runoff" during storms, and that water is anything but pure. It's loaded with stuff coming from the trees, ferns, mosses, fungi, bird droppings, etc.

2) Be VERY careful when watering with pure water, whether the source is distilled, deionized, reverse osmosis, collected rainwater, or A/C condensate; they all have so little dissolved chemicals in them that they are unbuffered, so will have the pH swing wildly upon the dissolution of even the lightest amount of soluble elements - solids or gases.

Pure water has a pH of 7. After a relatively short time, absorbed CO2 will form H2CO3 (carbonic acid) which lowers the pH. That's not a very strong acid though, so it won't do much to improve the buffering.

In my mind, the problem is what may happen when it comes in contact with chemical residues in the medium. As we really don't know what that chemistry is, we have no way to speculate on what the resultant pH may be.

[goodgollymissmolly]

Thanks for the comments, Ray. If someone went to the trouble to collect and look at canopy runoff surely they looked at more than just the trash in it. Hopefully they did some chemical analysis as well. Can you direct me to a reference for your information?

I have been using carefully collected rainwater for some time now. The pH upon collection is 6.9 everytime I collect new water. I pump it into a holding tank inside my greenhouse and after a period of weeks it is still 6.9. I actually expected it to drop slightly due to increased CO2 absorbtion. So far it has not. When I add 1/2 teaspoon per gallon of pure water formula GreenCare MSU fertilizer it may drop to 6.8 but no further.

You are correct that pH is most sensitive to changes in H+ and OH- ion concentration changes in the center region at 7. The math of that is pretty straightforward.

I don't agree with your comment about a weak acid (or base) not being a buffer. Actually you want a partially ionized substance as a buffer. When you add something else, the weakly ionized material reacts by adding more H+ or removing H+ (as the case may be) in order to maintain its own ionization constant. Using a completely ionized acid (or base) will not buffer the solution because it is already 100% ionized. However, in the case of CO2 and carbonic acid, I agree that it does not do much buffering because there is not much in solution.

I will measure some water that has been flushed through several different potting media to see what pH changes might be happening because you are correct that changes could be rapid.

Thanks for adding to this discussion.

[Ray]

Sorry, but I don't recall the reference, but yes, the chemical anlysis was done, and the most significant thing I recall was the level of nitrates.

I did not mean to imply that weak acids and bases were NOT buffers, just that some are not very good buffers.

[IdahoOrchid]

Originally Posted by goodgollymissmolly

I do not visualize the water in a tree to be a puddle of rotting vegetation. I see it as a flow of relatively pure water existing during a rain and shortly thereafter. Certainly it dissolves some stuff and wets the bark.

I guess I do not understand why you choose to dream up theories rather than joining me in asking for actual in situ data. Both of us can guessimate what happens til hell freezes over, but doesn't someone actually know from measured data?

Guesstimations are the first step to arriving at a solution. One must theorize first before any sort of action can be taken. You see, our guesstimated discussion has prompted someone that has access to orchid bearing trees to do some measuring for us!!!!

I do not suggest that the water must puddle or that sphag is the only thing that will acidify the water. Just the fact that the water is in contact with material other than air would change its chemical makeup. Ray's comments bear that out. Dead and rotting material in and around the roots would be great sponges that would absorb and hold the water for a period of time. If my understanding is correct, this would have a tendency to acidify the water. How long that would take and to what degree is still in question and would take experimentation. But you knew that coming from an engineering background.

So Dave (did I get that right???) there is your goal. Find some moist material that is in and around the roots of orchids or other tree dwelling plants and see what the PH is. A great experiment would be to get there right after a rain storm and measure it over a period of time: straight out of the air, collected as it runs down the branches and after it has accumulated in various places and ways.

Wish I could be there to help you.

As far as running water through various potting materials, that is a great idea too. Just as suggested above, see if the PH can be measured over a period of time within the materials to see if it changes during that period.

Still trying to figure out which meter I might get myself without spending a fortune.


Could someone please discuss a little more about the buffering aspect: what it accomplishes and what might be used. Also, how might using straight RO water might actually be harmful to my plants? Is straight RO unbuffered or am I confused?

[goodgollymissmolly]

OK, here is some rare factual information that clears up a lot of the discussion that we have had on this thread. I also want to correct (or admit, if you will) some incorrect data that I supplied to the discussion. I will correct the data as soon as I get new results.

First the facts that I have verified from multiple web resources including NOAA. The pH of rainwater in the "pure" sense of unspoiled earth is 5.6. This results totally from the solution of carbon dioxide which forms the weak (meaning partially ionized) acid known as carbonic acid, H2CO3. This is true worldwide since CO2 is a legitimate part of the atmosphere. All the global warming talk is related to increased CO2 not to the fact it always has existed. So the pristine jungle, in fact the pristine earth, sees rain at 5.6 pH. This confirms the current belief that plants including orchids see pH about 6 or a little below.

In actual practice, the rain in the eastern US, including mine, is closer to 4.5 to 4.7. This backed with lots of data that is collected to assess the impact of pollution on acid rain problems. The reason is that burning of fossil fuels (especially coal) puts oxides of sulphur and nitrogen into the atmosphere. When these dissolve into rain they form the strong acids, sulphuric and nitric
(H2SO4 and HNO3). These are fully ionized acids that reduce the expected pH. The western US is not as effected because of the prevailing west to east winds aloft....clears that up.

Now for my bad information..I reported my rainwater pH to be 6.9. I actually measured that repeatedly with a pretty good pH meter that was calibrated at 7 every time it was used. You should calibrate a meter at two points, 7 and 4 are commonly done. Well I skipped the 4 step. My meter is several years old and, in spite of my best intentions, the probe has dried out on occassion. So I need a new probe and some 4 pH standard before I start spouting off again. I apologize for the bad info. I HATE to do that.

Good news is that we can all go back to the old thought that orchids need their nutients supplied at about 6 pH.

Jim

[IdahoOrchid]

Thanks Jim. That is appreciated on multiple levels.

It should be noted that my comments were educated guesses intended to initiate additional conversation and not based on any hard facts readily known to me.

I am also not sure if it has been brought out, at least clearly, but it must be stated that this discussion it related to providing IDEAL or OPTIMAL rather than ACCEPTABLE conditions for watering and fertilizing plants and orchids specifically. Countless people have been growing and flowering countless species of orchids without a clue regarding this (and many other) topic. Your plants may not thrive, but should do well without the time and expense of implementing this information.

This has been a super great discussion. Thanks to all that have provided thought points and information.