about pH - Don't worry so much

[Leo Schordje]

I was going to post this in another thread, but rather than hijack a thread off topic, I will make this a free standing thread. Now I know there are exceptions, but I think as a general rule, for most Paph and the more common orchids the below is true. Ray - help me out if I am off base.

My personal opinion, pH is no where near as serious a problem as many make it out to be. I have worked for many years in a chem lab. There are a number of reasons why people should just relax and not worry so much about pH.

1. Plants have an ability to adjust the pH of the water film around the roots with their own exudates. This is why community pots work well for seedlings, and why not over potting is important. Plants will actively condition the environment around their own roots.

2. Focusing on pH is only half of the relevant parameter. You really need to know the buffer capacity of the solution also to know whether you have a pH problem. If the buffer capacity of the solution is low, the pH can be wildly out of what plants prefer, and the plants can very easily at very little metabolic cost buffer the water film around the roots into the ideal range for growth. If the buffer capacity of your water is very high, then even minor deviations of pH away from ideal ranges will overwhelm the roots natural capacity to buffer its environment.

3. Total dissolved solids (TDS) is a measurement that has some correlation to buffer capacity, but it is NOT a measurement of buffer capacity. It can be used to make a guess at buffer capacity. Examples:
* RO water & rain water have very low total dissolved solids, they also have very low buffer capacity.
* Well water around LaCrosse Wisconsin has a total dissolved solids about 1200 ppm, this is a dolomite karst area, mostly calcium & magnesium carbonates, this water has a very high buffer capacity
In a general way, Low TDS predicts low buffer capacity, high TDS predicts high buffer capacity. TDS can be used to make a GOOD ENOUGH TO BE USEFUL (not precise) guess as to the buffer capacity of the water. In this contex, knowing whether your buffer capacity is low, medium, or high is a "good enough to be useful" estimate.

4. Unless you have some lab experience with standardizing and calibrating pH meters you have no idea just how wildly inaccurate a pH meter can be. In certifying some of our products for the nuclear industry, I have hands on experience in making sure I have an accurate pH. If you do not calibrate your pH meter before use, you have a high probability of getting an inaccurate, sometimes a wildly inaccuate pH. This is with $4000 units. I can tell you from experience in trying to proof efficacy of $200 pH meters for use in our manufacturing process, the cheaper meters are even more difficult to get reliable results from. It is not that these cheaper meters don't work, it is that you can get 3 or 5 readings that are dead on, and then one will be wildly out. And you never know which is which. It is not worth the hassle of messing around with pH meters in a home setting. Especially if the water you are using has a TDS less than 250 ppm. The buffer capacity of water at TDS under 250 ppm is low enough that the majority of plants can compensate with their own ability to modify the water film immediately surrounding the roots.

5.) The pH of fertilizer solutions from the better fertilizer suppliers is 'close enough for folk' (music). Some of the better companies I am familiar with include Greencare, DynaGrow & the 'Pro' product line from Peters. They are close enough on pH that to worry about it is trivial. For example, if you start with RO water, and using the Greencare MSU RO formulation, if you measure a 5.6 pH and want 6.0, for a 120 ppm solution this is a trivial discrepancy, the plants will handle it just fine and any effort to get it closer to your ideal 6.0 is a waste of time and money. Also the adjustments have the risk of taking you even farther from where the plants want to be.

In summary, you should not discuss pH without a good understanding of where you are in terms of TDS. The pH of low TDS solutions is usually trivial except for a few special case situations. If you are using RO water, worrying about pH is a waste of time because buffer capacities are so low.

Edit Sat, Jan 23, 2010
Two things I did not add to the original post, and probably should have.

(1.)When I did use pure RO water (I don't any more due to expense and having 'good enough' municipal water) I never watered with pure RO water, I always added at least 1/4 teaspoon per gallon of MSU fertilizer. Never would I do a pure RO flush watering of the plants. Putting a little fertilizer in seemed to keep the plants from developing chlorosis. Personally the last few years I have been fertilizing at 1/2 teaspoon per gallon continuously with every single watering. I don't bother with the 'clear flush' that many promote. I figure I like to eat everyday, I assume the orchids like to eat every day.

(2.) I do not dry plants out all the way between watering. I will let them get near to dry, but I have my best results by NOT drying the plants out. I tend to grow rather wet. When I get leaf tip die back it is almost always after a hard drying out. Leaf tip die back can be prevented by growing a little wetter. When growing 'wetter', it is important to make sure you have air movement, and I do pay extra attention to making sure there are planty of air voids in my potting mix. For my potting mixes, before using them, I do discard all the material that passes through a peice of window screen (approx 1/8 inch seive).

I do dry out plants with specific dry season requirements. I do this by physically taking them out of the growing area and putting them somewhere else so I don't forget and water them.

 

[Lanmark]

Great info! Thanks!

Sigh. I wish I were smart like Leo and so many others around here, but at least I can tell you how to make mud...

 

[Brabantia]

Very interesting discussion and effectively a special thread on this subject is more appropriate. Me too I was working 27 years for a American chemical company as QC manager (the mother company was established at Indianapolis Indiana). I understand very well what you explain and it is the reason why I prefer mix a little bit tap water (5%) with my fertilyser solution prepared with rain water. In my country of Belgium the tap water is very hard, equivalent to around 450 mgr calcium carbonate for 1 liter. For your information this morning I prepared a fertilyser solution at 100 ppm N with rain water and and this has necessitated 8 drops of KOH 1M to climb the pH from 5.6 to 6.2. I also agree with the existing difficulties to correctly calibrate a pH meter. Calibrate your pH meter, make your measures and reverify your calibration... the results are often frustrating!

 

[etex]

Very well put, Leo!! Thanks for the information! I'll use my RO water and RO fertilizer and leave the rest to you chemists!!

 

[Shiva]

Leo! I have a fail safe way of determining if pH is OK. I look at the plants and if they're growing well and flowering well and have bigger and bigger green leaves and no burn tips, the pH is OK.
Works every time.

 

[Lanmark]

Leo! I have a fail safe way of determining if pH is OK. I look at the plants and if they're growing well and flowering well and have bigger and bigger green leaves and no burn tips, the pH is OK.
Works every time.

Hehehe... I have ph-bots. They are teeny tiny nanites and they go to work each time I put solution on my plants. They correct any errors they find and report back to me at once with suggestions how I can do better next time. :wink:

 

[Shiva]

Hehehe... I have ph-bots. They are teeny tiny nanites and they go to work each time I put solution on my plants. They correct any errors they find and report back to me at once with suggestions how I can do better next time. :wink:

Man! I would love to get some of them. Maybe I could reprogram them to lose weight! oke:

 

[SlipperFan]

Thanks, Leo. You've confirmed my prejudices.

 

[Brabantia]

Leo! I have a fail safe way of determining if pH is OK. I look at the plants and if they're growing well and flowering well and have bigger and bigger green leaves and no burn tips, the pH is OK.
Works every time.

if not, it is often too late to correct, especially for Paphios!

 

[aquacorps]

Leo, I use DI water and ph issues have almost killed my collection. ph is an issue with DI water. This is from a web site:

Pure water by definition is slightly acidic and distilled water will test out around pH 5.8. The reason is that distilled water dissolves carbon dioxide from the air. It dissolves carbon dioxide until it is in dynamic equilibrium with the atmosphere. That means that the amount being dissolved balances the amount coming out of solution. The total amount in the water is determined by the concentration in the atmosphere. The dissolved carbon dioxide reacts with the water and finally forms carbonic acid.



Read more: http://www.lenntech.com/application...ionised-demineralised-water.htm#ixzz0dREcC9ss

 

[Shiva]

if not, it is often too late to correct, especially for Paphios!

I don't think I''ve ever lost a paphio because of a pH imbalance. But in 30 years I lost many orchids including paphios because, among other things, I didn't know how to grow them, or the litterature about them was confusing, or I waited too long to repot them, or I didn't react fast enough to insect damage. Even then, I accept the losses as part of the learning process and I don't worry too much about pH, fertiliser or whatnot. This is still a hobby and I'm not going to lose sleep over one paphio or phal that didn't make it. Orchids are living things and they always do one of three things: live and prosper, sulk forever or die, just like people.

I have a collection of some 500 mixed orchid generas and the majority of them are doing just fine. So I must be doing mostly right.

 

[etex]

I just got an RO system 1 month ago. Who knew it was so controversial! All my plants are growing well and the arial roots look great!
Started my repotting yesterday and am very happy with the amount of new growing root tips I found on many of my paphs when unpotted! That's the kind of feedback I like to see!!

 

[Leo Schordje]

Leo, I use DI water and ph issues have almost killed my collection. ph is an issue with DI water. This is from a web site:

Pure water by definition is slightly acidic and distilled water will test out around pH 5.8. The reason is that distilled water dissolves carbon dioxide from the air. It dissolves carbon dioxide until it is in dynamic equilibrium with the atmosphere. That means that the amount being dissolved balances the amount coming out of solution. The total amount in the water is determined by the concentration in the atmosphere. The dissolved carbon dioxide reacts with the water and finally forms carbonic acid.
Read more: http://www.lenntech.com/application...ionised-demineralised-water.htm#ixzz0dREcC9ss

Without knowing all the details of your growing set up and methods, I am still doubtful that pH alone was the issue. I remember the original post where you discussed this problem, I was not able to figure out what the source of your problem was, the discussion was long and there was a lot of back and forth between you and Ray & a few others. I think there was something unique in the way you were doing things that resulted in your problem. I think your situation was a special case. Something in the combination of your technique and your water and fertilizers were creating the 'perfect storm' that caused your loss of plants. It won't be helpful to rehash this here. This post is intended as a rough idea of what is 'good enough' for most average growers. This method certainly works for me.

Two things I did not add to the original post, and probably should have.

(1.)When I did use pure RO water (I don't any more due to low water pressure causing it to take to long to make and having 'good enough' municipal water) I never watered with pure RO water, I always added at least 1/4 teaspoon per gallon of MSU fertilizer. Never would I do a pure RO flush watering of the plants. Putting a little fertilizer in seemed to keep the plants from developing chlorosis. Personally the last few years I have been fertilizing at 1/2 teaspoon per gallon continuously with every single watering. I don't bother with the 'clear flush' that many promote. I figure I like to eat everyday, I assume the orchids like to eat every day.

(2.) I do not dry plants out all the way between watering. I will let them get near to dry, but I have my best results by NOT drying the plants out. I tend to grow rather wet. When I get leaf tip die back it is almost always after a hard drying out. Leaf tip die back can be prevented by growing a little wetter. I do dry out plants with specific dry season requirements. I do this by physically taking them out of the growing area and putting them somewhere else so I don't forget and water them.

 

[Ernie]

All, note that Leo's 1 & 2 are very important! If you do #1 (feed continuously OR have high TDS water) you should do #2 (grow on the wetter side not allowing mix to dry). Why??? When the water evaporates away, it leaves behind all the junk (salts) that burn and damage roots. If you constantly keep the salts in solution by growing more moist, they're not as damaging. If you grow wet, though, you might want to adjust your mix so it doesn't break down as fast, or plan to repot more frequently. ALL things in culture are tied together!

-Ernie

 

[cnycharles]

good points... my phrags usually did poorly because I would allow them to dry out (not by design) and the leaves would burn. about leo's point about how he uses somewhat weak ppm's all the time, I'm starting to try and not drink the pure water that we get at work and at home (it is very low ppm's and tds) since I read that world health organization thing about very pure water and health issues. it isn't much, but I try and toss a little fruit juice or some dried ice tea mix into the water so it's a little 'harder'. (just my preference) I actually love the water where I grew up (hard, lots of calcium and such, tasted very good) but can't get that here. there is lots of limestone around (smile), maybe I should toss a few pebbles into a bottle and let it sit a bit before drinking it!

 

[Ray]

Leo, I use DI water and ph issues have almost killed my collection. ph is an issue with DI water. This is from a web site:

Pure water by definition is slightly acidic and distilled water will test out around pH 5.8. The reason is that distilled water dissolves carbon dioxide from the air. It dissolves carbon dioxide until it is in dynamic equilibrium with the atmosphere. That means that the amount being dissolved balances the amount coming out of solution. The total amount in the water is determined by the concentration in the atmosphere. The dissolved carbon dioxide reacts with the water and finally forms carbonic acid.

RO, DI, distilled, and collected rainwater all suffer from the flaw of bearing little-to-no mineral content. In their pure form, they are totally pH neutral, not acidic. The fact that they can absorb carbon dioxide to form carbonic acid is, however, true. If you store your pure water in contact with brass, for example, that acidity will dissolve the zinc from the brass, leaving you with a porous, brittle, copper piece. However, if you add any fertilizer to that water, its minerals will overwhelm the carbonic acidity so well, it's as if it wasn't there in the first place.

This is probably just a matter of interpretation, or simply that of point-of-view, but - agreeing with Leo - the only thing you need to be concerned with is using the correct fertilizer for your water supply. Trying to adjust the pH ever so precisely is indeed, a waste of time. The problem posted over at GardenWeb that started this whole discussion was the use of a fertilizer intended for mineral-bearing (buffered) water with the essentially mineral-free, relatively unbuffered NYC tapwater. The result was a solution with a pH damagingly low.

 

[PeteM]

Thanks for this thread, the info on this forum is very helpful.

I've converted to RO in the last year and have been monitoring pH, which seems to be less important with low TDS. My crappy calibrated pH meter still manages to concern me ( I fear the log scale) as I often read in the low to mid 5's after adding small amounts of MSU, TDS meter reads 50-80 ppm. The scale still worries me enough to add pH UP to get the pH into the 6's. Now I am concerned about overexposure to pure RO (chlorosis) as I do water with a hose straight from the RO reservoir (30 Gallons) for the dailies, Vandas, Phrags, mounted and about once a week to properly soak others in the collection.

However, my daily routine also includes mixing a 1 gallon pump spray of RO with 50-80 ppm of fertilizer. I lighty wet the roots / top of pots for the entire collection. This is done 20 minutes prior to watering with RO. Should I reverse this process or add another layer of lightly 'buffered' RO water at the end of this process? Also open to suggestions or solutions others have tried with RO. Mixing tap back into the reservoir, does this buffer the RO enough to stabilize pH?

What if you just add pH UP (potassium hydroxide and potassium carbonate) to 'buffer' RO, is that better than tap?

 

[littlefrog]

You could try using pH paper... Especially if you don't have the equipment or expertise to properly calibrate a meter. I've used pH paper for years, especially when I change fertilizers or try something new, just to be sure I'm in a reasonable range.

Like Leo, I don't worry about pH as long as I'm within some sane range of starting values. pH paper is good enough for that.

 

[Tony]

I have been using RO for about a year and a half now, typically with K-Lite and other supporting products but also using straight RO for an occasional flush or bout of laziness and have had no issues with chlorosis. Quite the opposite in fact, my plants look better than they ever have before in nearly three decades of growing.

 

[abax]

Leo, this thread is priceless. I mix RO with tap and
K-lite and it's working quite well.