Salt tolerance levels

[gonewild]

I would like to start a discussion about salt tolerance of paphs and phrags.
Please everyone put in your comments and experiences.

It is commonly accepted that paphs and especially phrags have a very low tolerance of salts.

Does anyone know what level is considered safe or unsafe?

I'm curious how this became common knowledge and if there is any published information that identifies what level is the boundary?

P. besseae is particularly sensitive to salts. What is the maximum level of salts in irrigation water it will tolerate without damage.

Is the problem with total salts or one salt in particular?

 

[lothianjavert]

I can't help with any additional information, but it would be great to have a factual base for salt tolerances! Interesting thread, thanks for starting it!

 

[Rick]

Lance. This question may get complex because of problems to separate out the accumulation of salts in the potting mix versus how much can be tolerated in the irrigation water. Another complicating factor is the difference between acute (short term mortality) versus long term chronic (growth inhibition effects, but not dead).

I try to apply my experience with aquatic toxicity to freshwater organisms. Basically the divalent cations (Ca, Mg) are less toxic than the monovalents (Na, K). I have seen our water fleas tolerate 2 or more times the TDS of a mix that contained mor calcium than the other cations.

Also HCO3 is more toxic than chloride which is more toxic than sulfate.

I know that K is part of a fertilizer mix so I can't tell at this point of plant will naturaly have greater tolerance to K than water fleas.

I don't have any good test numbers for orchids, but I do have them for a freshwater algae. Our Selenastrum sodium chloride LC50 is about 1500 mg/L in water with a hardness of 80-100mg/L (as CaCO3).

Detectable effects to growth of the selenastrum culture happen at about 2/3 the acute value.

 

[gonewild]

Yes it can get complex. That's OK we can wade through it. And we can eventually word it so everyone can understand.

It would be nice to hear some kind of reason to assume paphs and phrags are salt sensitive that is based on some measurement.

Is the problem apparent when people use tap water without fertilizer or when fertilizer is added?

Has anyone read TDS to determine at what point a problem occurred?

How many PPMs of total salt will cause a problem with P. besseae?

I suspect the sensitivity has grown by word of mouth to the point where people are afraid to fertilize their plants. And to the point that some people are afraid to try to grow some genera.

 

[Ray]

Lance,

As Rick said, isn't that "ppm's of total salt" question mighty dependent on what mineral salt(s) is/are involved, meaning there is no single answer to that question?

Seems to me that "X" ppm of NaCl is going to be tolerated a lot less that the same concentration of MgSO4, as an example.

 

[gonewild]

Ray,

Of course different salts will have different tolerance effects.
There can be many answers to the question.
So let's answer them. We don't need just one answer.

You mentioned sodium.... How many ppm of sodium will phrags or paphs tolerate?

Here is a simplified 2 part question to get us started...
Do you know for a fact Phrags are more sensitive to salt than other orchids?
How do you know this?

Here is a part question....
How many PPMs of total dissolved salts will a Phrag. besseae tolerate before it is visibly damaged?

And an overview question.....
What is considered the maximum salt tolerance of paphs and/or phrags?

 

[Leo Schordje]

My experience says the salt tolerance issue is a bit of a red herring. More often than not. When I see a set up where the grower is complaining about lack of salt tolerance, I find the Phrags are grown too dry. Grow the Phrags wetter. Salt won't be as much of an issue. I grow my Phrags standing in water. My irrigation water runs 900 ppm. I start with 220 ppm Lake Michigan municiple tap water. I add 1/2 teaspoon MSU fertilizer per gallon with every watering. This means 24/7/365 my Phrags are in a minumum of 925 ppm water. If the trays start to evaporate, it may even get a bit higher. I do flush the trays with each watering. I have no trouble with leaf tip die back - as long as I keep the Phrags wet. Most of the time, leaf tip die back is the direct result of being too dry. Think of Phrags as Aquatic Cymbidiums, not as upland forest plants. If you use the same water for your Phals, Cattleya & Paphs that you use for your Phrags. And you have no leaf tip die back on your other genera, but your Phrags show leaf tip die back. The problem is not the water, but the person doing the watering. Phrags want it wetter. Damp as you would keep a Paph is too dry. Keep them WET.
My 2 cents worth.
Leo.

 

[gonewild]

My experience says the salt tolerance issue is a bit of a red herring. More often than not. When I see a set up where the grower is complaining about lack of salt tolerance, I find the Phrags are grown too dry. Grow the Phrags wetter. Salt won't be as much of an issue. I grow my Phrags standing in water. My irrigation water runs 900 ppm. I start with 220 ppm Lake Michigan municiple tap water. I add 1/2 teaspoon MSU fertilizer per gallon with every watering. This means 24/7/365 my Phrags are in a minumum of 925 ppm water. If the trays start to evaporate, it may even get a bit higher. I do flush the trays with each watering. I have no trouble with leaf tip die back - as long as I keep the Phrags wet. Most of the time, leaf tip die back is the direct result of being too dry. Think of Phrags as Aquatic Cymbidiums, not as upland forest plants. If you use the same water for your Phals, Cattleya & Paphs that you use for your Phrags. And you have no leaf tip die back on your other genera, but your Phrags show leaf tip die back. The problem is not the water, but the person doing the watering. Phrags want it wetter. Damp as you would keep a Paph is too dry. Keep them WET.
My 2 cents worth.
Leo.

Very good info Leo! This is the type of information I hoped to drag out.

It seems most people believe phrags require pure water (RO). Many people don't fertilize near enough because they are told the plants will burn up with the salts. Your levels of 925 ppm are approaching normal levels for most plants.

Have you ever had your salinity levels higher? What are the levels when your tray water evaporates? I assume your pots and roots sit in the tray water?

Do you grow all Phrags under these same levels?
species vs. hybrids?
seedlings vs. mature plants?

 

[Leo Schordje]

Hey Lance,
Unfortunately, the only place I have time to play scientist at is at work. At home (with the orchids) I am as non-technical as possible. The 925 ppm TDS I cited on my water is by calculation. Not by direct measurement. Our water district cites that our village source is Lake Michigan tap water, now about 225 ppm. The 1/2 teaspoon per gallon of the MSU-Orchid for RO (Green Care's Plug Special) fertilizer is about 700 + ppm by calculation, so that is how I got there. I never checked to see how high it climbs as the trays evaporate. I try not to let the evaporation progress very far. I want the Phrags wet.
*** I grow all my Phrags the same way including my Phrag kovachii seedlings from Alfredo Manrique. For the kovachii I added some oyster shell to the seedling bark mix. For Phrag caudatum and kin, I use a medium grade bark instead of seedling grade. I keep caudatum very wet, but in a more open mix. I also make certain my caudatum are in the brightest, & breezy spot in the light garden. Caudatum blooms should open within the week.
Hope this helps
Leo

 

[Rick]

Out of the 925 ppm of TDS there is probably less than 50-100ppm of sodium. Probably none from the fertilizer, and most surface waters in the midwest and east are fairly low.

As far as the selanastrum (algae) example goes, the amount of sodium at its LC50 is about 600 ppm.

 

[gonewild]

I think the opposite is true of water in the west. Most water out here is high in sodium to the point of being bad for irrigation. I suspect sodium is actually the "salt" that earned orchids their reputation of being salt sensitive?

This is what should be understood about fertilizing orchids. Not all salts are harmful. To limit total salt levels to a few hundred ppm not only limits possible sodium toxicity but it also limits the important nutrients plants need.

Have orchid enthusiasts taken the term "salt sensitive" to the extreme and made it a general growing recommendation which results in under fertilization?

I think so.

 

[Rick]

I think you're right. But I think there is the potential for some problems with amonium salts too. Amonia at pH's around 8 and up can be very toxic compared to sodium chloride.

So I think calcium nitrate is the way to go to get nitrogen into plants that like pH ranges in the 7-8 range.

 

[gonewild]

Calcium nitrate should be the base ingredient for most fertilizers. It probably would be if it was cheaper.

I've never dealt with ammonium toxicity, probably because the pH has never been above 8 with what I have worked with.