Salts from fertilisers

[Stone]

Mike, You are confusing precipitation with evaporation.
The salt build up growers are concerned about is caused by evaporation not precipitation.

I don't think I am confusing the two. I made some attempt to distinguish between them.
There can only be a salt build up if more goes in at the top of the pot than comes out the bottom.

Precipitation is when a chemical reaction between two dissolved chemicals from a new compound and that compound falls out of solution as a solid. That does not easily happen in wet soil media.

I think now maybe you are confusing precipitation with increasing concentration.
Precipitation can easily occur in water. Mix cal nitrate and ammonium sulphate together (even small amounts) in water and you will see.

Evaporation on the other hand is what causes salt build up in growing media.

It's not build up it's increasing concentration as water level decreases

salts left behind by evaporation (crystals) are easily redissolved when they come back into contact with moisture. This is what caused water in the potting media to become too salty.

You won't get much in the way of crystallization in the media unless it dries out. That's why you often see incrustations around the drainage holes or on the outside of a clay pot but not in the mix itself. And that's where correct management of water and salts is needed. So what exactly is the issue? Isn't that what we all do (correctly manage) when we successful grow a plant in a pot?

 

[Bjorn]

Lots of interesting reading; and lots of misconceptions.
Why not just reduce fertilisation level and increase watering? Then salts buildup will be much less of a problem.
There seems to be a conception amongst many ochidists that water is necessary but dangerous; so they try to water as little as possible - and never in the crown!.
As if it is not raining where the plants grow.......in my opinion many problems are related to cultural factors other than getting wet or not.
reverting to the issue about so-called salts deposits, these are normally insoluble and consist of not only carbonates like Calcium carbonate, but also silicates. Silica is, opposite to common belief, fairly soluble, up to 50-100 ppm as monosilicic acid. This Depends on the sopurce however silica sand is not very soluble, while DE is highly soluble (ok its not very soluble more the 50ppm range). Upon drying the monosilicic acid polymerises to polysilicic acid , and this is not soluble. If watering is withheld until the deposit is formed, it will become significant and may possibly create problems.

 

[Ozpaph]

To address kiwi's question.
I use and have not seen problems with perlite (with bark and charcoal). I have had, as have many, problems with diatomite. Coir is too unpredictable. I have had bad experiences with it - so never use it. Im told the 'pre-treatment', at its source, is highly variable and determines its usability (too much sodium, I understand). many have moved away from it here.

You have the best bark in the world, I'd use that!

 

[Ray]

Sorry Lance. "Precipitation" is any formation of a solid species from a liquid solution, whether it involves the formation of a new compound or not. "Evaporation" is the conversion of a liquid to a gas, whether anything drops out of solution or not.

In our context, evaporation of the solvent (water) causes the concentration of the dissolved solutes (nutrient chemicals and plant wastes) to exceed their maximum solubilities, therefore precipitating out of solution.

Bjorn, you are absolutely correct that decreased concentrations and increased watering - both volumes and frequency - will reduce the buildup rate.

Mike, all media will build up minerals eventually. LECA in S/H culture that is flooded frequently may take a very long time, but it's not never.

 

[consettbay2003]

Gonewild

How long does it take for plant roots to die when the mix becomes dry?

 

[Stone]

Mike, all media will build up minerals eventually. LECA in S/H culture that is flooded frequently may take a very long time, but it's not never.[/

If that were the case, then the ''build up'' from rain deposits in the habitat over the eons would destroy all plant life. It is a question of balance between what goes in and what comes out. Very simple. If there is a build up to a level where growth is affected, then not enough is coming out.

Let me give an example.
Every year, (in a natural forest in Yunnan) there is 0.49N 0.05P 0.15K 0.35Ca 0.13Mg 0.08Na 0.14S brought in by rainfall. (in fact there is much more added by leaching from tree leaves etc.) That does not seem like much - and it isn't - but it is deposition all the same. If there where a ''build up'', how much of these minerals would be there in 1000 years? The answer of course is exactly what is there now and what was there 1000 years ago because there is no build up.

So the epiphytic plants have evolved to exploit that flux of minerals.
There is no reason why the same balance cannot be achieved in cultivation.
If there is a build up of certain salts in LECA for example, it shouldn't be impossible find out what they are and balance the nutrient flux accordingly.
After all, natural humus potentially holds much more water/nutrients than leca. Are we still over fertilizing or giving the incorrect ratio of nutrient elements?

 

[gego]

I agree with Mike. Eventually the system will be in equilibrium and there will only be so much build up as the system can sustain. The variable here is the amount of water/rain, the amount of mineral and the holding capacity of the material. A balance will be achieved for our dear plant to grow.

Example of a good deposit of mineral is the formation of stalagmites and stalactites. Water with lime (Ca) drips at a rate to sustain build up. Too slow or too fast will have a different result.

 

[Ray]

Aw, c'mon.

I hardly think one can compare a natural ecosystem containing many, many species of flora and fauna to that of a plant in a flower pot...

Example of a good deposit of mineral is the formation of stalagmites and stalactites. Water with lime (Ca) drips at a rate to sustain build up. Too slow or too fast will have a different result.

Different, but still a buildup, as is also the case for differences in Ca concentration. That is a case of constant flow, never drying, and yet still precipitation....in a natural environment.

 

[C. Rothschild]

Vitamin B1 and liquid seaweed are both supposed to be good for orchids. Also pouring through a coffee filter may help. But yes I assume anything can build up in the pot. If you have some moss on the top you could just pick it off and replace it a couple times a year.

 

[Ray]

A coffee filter is not going to affect dissolved minerals at all.

 

[Rick]

http://www.slippertalk.com/forum/showthread.php?t=31056&highlight=potassium&page=3

I threw this old thread back in because it illustrates the importance of CEC of different mix components

In this experiment conducted by the Orchiata folk a ways back, it shows that the low CEC substrate (Orchiata) retained the least amount of K from fertilizer (under supposedly identical water and feed rates) compared to moss and coconut coir. In fact Orchiata only retained about 1/2 to 1/3 the amount of K compared to coir.

This also affected the amount of K going into the leaves and roots of the plants (in this case a hybrid Phalaenopsis), although for this (short) study, no significant difference in plant growth was noted.

I've seen plenty of other studies on the use of coconut products that demonstrate that once it gets loaded with monovalent cations (Na and K for most purposes) you can't get it out of the mix no matter how much you soak it in pure water. You need to soak it in a high concentration bath of calcium and magnesium salts to draw it out of the media.

Using a low CEC media retains less monovalent cation (or ionic forms in general) and easier to "flush".

But as Bjorn stated if you don't add concentrated fertilizer salts in the first
place you can water to your hearts content and not have to worry about flushing to clean out the retained salts in the mix.

 

[gonewild]

You need to soak it in a high concentration bath of calcium and magnesium salts to draw it out of the media.

Which you cant do with a plant growing in the media.

 

[Rick]

Which you cant do with a plant growing in the media.

Yup which is probably where the tradition of repotting came from.:wink:

 

[Stone]

[

This also affected the amount of K going into the leaves and roots of the plants (in this case a hybrid Phalaenopsis), although for this (short) study, no significant difference in plant growth was noted.

That's because K usually doesn't cause any problems.

 

[Rick]

[



That's because K usually doesn't cause any problems.

Lack of K doesn't seem to cause any problems either. So why do we insist on wasting so much?

 

[Rick]

Remember the original question of this thread was how to manage salts in potting mixes.

Given that his irrigation water (rain or RO) the only salt going in is going to be from the fertilizer (which depending on choice is mainly K as an accumulating ion).

So the management answer is "it depends" on:

1) choice of fert mix
2) frequency and concentration of fert application.
3) choice of potting mix.
4) frequency of non feed irrigation rate
5) frequency of repotting.
6) pot size and configuration.

The way I feed and water has made items 3,4,5, and 6 almost irrelevant in mine and others collections.

Back before 2011 when I used MSU pure water in RO water I was constantly in the strategy battles of potting mix / pot / repot wars. Now these are the least of the things I worry about.

 

[Stone]

Lack of K doesn't seem to cause any problems either. So why do we insist on wasting so much?

Because I like to give my epiphytes close to what they receive in the habitat.

Unless there is something I have not seen, over a year, they get as much K as N. (sometimes a bit more, sometimes a bit less) The ratio Rick not the concentration. During the wet, the amount of K coming from trees can far outweigh the total N coming to the plants. This perhaps does not account for N-fixing microbes in roots or on leaves, however, from what I have read, estimates for this N source are significant but still a low percentage

I have not seen data for limestone species so I presume they get a little less.
However, it does not seem to make much difference judging by some of the examples of brachys etc posted here and elsewhere.

I agree that low salt concentration is best but I cannot agree with the low K to N concept.

 

[Russ1992]

Remember the original question of this thread was how to manage salts in potting mixes.

Given that his irrigation water (rain or RO) the only salt going in is going to be from the fertilizer (which depending on choice is mainly K as an accumulating ion).

So the management answer is "it depends" on:

1) choice of fert mix
2) frequency and concentration of fert application.
3) choice of potting mix.
4) frequency of non feed irrigation rate
5) frequency of repotting.
6) pot size and configuration.

The way I feed and water has made items 3,4,5, and 6 almost irrelevant in mine and others collections.

Back before 2011 when I used MSU pure water in RO water I was constantly in the strategy battles of potting mix / pot / repot wars. Now these are the least of the things I worry about.

Rick if points 3-6 are no longer primary concerns then did you do with points 1-2 differently that has led to such success? Many people tout the wonders of MSU combined with RO water.

 

[Ray]

Rick’s comment was 8 years ago and I don’t know if he hangs around here much these days.

( I hope I can express this well enough to be understood

There are two factors to deal with, “accumulation” and “precipitation”. They are related, but for this discussion, not synonymous.

Accumulation is more about the affinity of the medium to trap and hold the mineral ions. A reasonable analogy is a cellulose sponge. When soaked in a solution, some of the solute components may be chemically attracted to the cellulose, so will weakly bond with it, accumulating more with time and further exposure. Such accumulation can occur throughout the potting medium column.

Precipitation is almost totally due to evaporation of the solvent - water - and occurs primarily on the top of the potting medium column. Sure, it can be related to concentration and the reaction of solute ions, as happens when one attempts to make a concentrated solution or calcium nitrate and Epsom Salt, resulting in the precipitation of gypsum, but in this context, I’m referring to precipitation in even the most dilute, stable solutions.

The way to minimize that, in addition to the use of dilute fertilizer solutions, is to prevent drying of the media.

 

[Russ1992]

Rick’s comment was 8 years ago and I don’t know if he hangs around here much these days.

( I hope I can express this well enough to be understood

There are two factors to deal with, “accumulation” and “precipitation”. They are related, but for this discussion, not synonymous.

Accumulation is more about the affinity of the medium to trap and hold the mineral ions. A reasonable analogy is a cellulose sponge. When soaked in a solution, some of the solute components may be chemically attracted to the cellulose, so will weakly bond with it, accumulating more with time and further exposure. Such accumulation can occur throughout the potting medium column.

Precipitation is almost totally due to evaporation of the solvent - water - and occurs primarily on the top of the potting medium column. Sure, it can be related to concentration and the reaction of solute ions, as happens when one attempts to make a concentrated solution or calcium nitrate and Epsom Salt, resulting in the precipitation of gypsum, but in this context, I’m referring to precipitation in even the most dilute, stable solutions.

The way to minimize that, in addition to the use of dilute fertilizer solutions, is to prevent drying of the media.

@Ray Do you prefer that users create new threads for the same related topic if the original thread is over "x" amount of years old? I would think it's better to keep the discussion in the same thread if it's about the same material or in direct reference to a previous post. In this way, the context is not lost and there aren't 24 new threads relating to the accumulation of salts (an exaggeration but you get my point); too many threads lead to difficulties in finding content relating to the same theme. I'm not saying this to be catty but I know you have your reasons and I genuinely don't know what they are.

If a medium traps and holds mineral ions is it a good thing or a bad thing?
Assumption 1: If it traps and holds ions ( like a filter membrane ) then I would think the solution the plants receive isn't as mineral-heavy as it otherwise would be and becomes a benefit; I think this is what Dave @Paph Paradise would say about Charcoal. If this assumption is true then the salt would have to travel deep enough into the particle of media to minimize physical contact with a root.
Assumption 2: If the medium traps more and more ions and thereby releases more and more ions into the solution then one would assume something like Charcoal would be a detriment to the plant.

What's worse too high of TDS or too low in fertilizer?
Not letting the media dry out seems to go well with the semi-hydro approach but that also means flushing I would think is critical if the roots are constantly soaking up a solution with a high TDS. The common sense response would be to fertilize less if you're using a mineral-high tap or well water but the potential consequence is the plant not getting enough of some critical nutrients like Nitrogen.