Does a free draining mix reduce soil salt build up

[Bretts]

It is a common theory that a free draining mix will allow the salts to be washed out of our pots soil. Makes sense and I never thought to doubt it.

Since Reading an article about Hornbeam care by Walter Pall in Bonsai Today magazine #70 Where under watering he suggests that a salt intolerant plant such as Hornbeam if you are using a medium that dries out frequently then you should use rain water to avoid salt buildup.
He doesn't actually say a free draining mix but to me that is what he means.

Now this was confusing as Walter often states that we can use whatever fertiliser we like and a free draining mix will wash away what the tree does not want to use! Now if this was from anyone else I might have shrugged it of as some one making things more difficult that need be but being Walter who is the KISS king I could not ignore it.
So when I gave it some thought it did start to make sense in that we can see residue buildup where something is constantly wet and then dried. I considered this was also the case in a free draining mix. The more often you have to water the more residue will be built up. We say we can wash it away when watering and I am sure we can wash some away but when you consider the build up that can be seen as leaching on a low fired pot, That can not be washed away so It makes sense that the same sought of fired clay substrate in our soil is also getting this residue that can't be flushed away with a heavy watering.

This article is 10 years old so maybe Walters views have changed. I will have to try to ask him about this but what do you guys think?

Also it was suggested to me that a medium with a high CEC value may aggravate this issue but recent reading has suggested that it actually helps alleviate the problem? Or maybe stopes high fluctuations is a better description of a high CEC.

[Ash]

My understanding is that the porosity of the granules themselves is of equally high if not higher importance than the proportion of space between the granules.

For example I grow Cooktown Orchids. In a fertilizer treatment I grew a batch of plants in pure granite chips (25mm chips) in 100 mm pots, a batch in coconut husk chips (same size) and a batch in basalt scoria (same size). They all drained freely and were bone/biscuit/wooden god dry by nightfall. I did not ever measure the rate of drying in the day. They were all watered with equal frequency. After 12 months of weekly fertilizing I had the nurtient content of the roots and the growing medium tested and compared with measurements taken at the begining. The roots of the orchids grown in coconut had several fold higher NPK and salt content (and the coconut husk retained salt). Due to the other two batches being grown in rock I could not have the NPK or salt content of the mix tested, only of the roots of the plants.

In bonsai mix I see more surface salts on plants grown in my bark and scoria (Atherton Mt Quincan) blend then I do in my leaf humus and granite (local creek) sand blend. Both are watered the same time each day. Never had any testing done.

If you are worried about excess salt catch some rain and give the plants a good soak, then a good flush with new water. Might get rid of some.

keep the responses comming
cheers

Ash

[Bretts]

Thanks Ash I will consider this. Just wanted to say The new rain water tank is getting it's first fill today

[63pmp]

Brett,

“Where under watering” is the crucial element of Waltar's statement.

Let’s look at it from a different perspective. Any type of water will have small amounts of material dissolved in it. These are usually metallic and non metallic ions, in other words, elements with some kind of charge. Table salt is the most common, Sodium Chloride, made up of the atoms of sodium and chlorine. During a chemical reaction the metal, sodium gives an electron to the non-metal, chlorine, (which is now called chloride to indicate it is an ion). These atoms now have equal but opposite charges, sodium positively charged, chloride negatively charged; these charged atoms are called ions, cation for positive, anion for negative. When dissolved in water, each ion is free to move away from its opposite ion due to the effect of water molecules, it dissolves in other words. There are many types of salts, when people talk about salt in soils, they are talking about many different types, not just sodium chloride. A fertilizing solution is a solution of salts; so is plain tap water, or rain water, the amount of salts dissolved varies considerably. Compare rain water to sea water. (incidently soils affected by high sodium chloride levels are called sodic)

When we water a plant, the potting mix will hold a certain amount of water. The rest runs away out the bottom of the pot. The plant then absorbs water from the mix to maintain growth, it will also remove a small amount of the salts applied to the potting mix. The plant will not remove all of the dissolved salts that have been applied. The plant (with evaporation) will however remove all the water in the potting mix so that the remaining solution becomes saltier. If there is enough salt remaining in the potting mix it will damage the plant.

When we water again, the remaining salts from the previous watering will dissolve into the new water, and perhaps be washed out, or remain in the potting mix. If you only water with a small amount, and have minimal runoff, then you will have whatever salt is left over from the first watering plus any newly added salts. The plant removes water again but the remaining solution is saltier than the first solution. This continuous for however long you keep watering without a good flush, eventually salts may even precipitate out of solution.

It doesn’t matter what the porosity of the potting mix is for this to occur. You just have to under water. It is easier to flush salts out of a porous mix as water flows through it rapidly, removing excess salts. I fine mix will be more difficult. It is the amount of water flowing through the potting mix that is important, the more water the more salts leached.
Rain water is best as it has very low salt levels. (Mind, the zinc salts in rain water from a corrugated iron roof can be high enough to kill a plant, so it depends on where you collect your water.)

The white precipitate that forms on pots is a build up of calcium and magnesium phosphate salts. This stuff is insoluble it does not harm the plants. Plants actually eat this stuff as they excrete acids to dissolve it.

Fine material such as weathered pine bark or zeolite have very small pores which allow water and salts to enter it. It takes a lot of water to wash these out again, simply because water will not flow through the bark ( due to a thing called tortuousity, the more tortuous a path the less likely water will take it) Bark and zeolite dry white due to osmosis sucking water and salts form the inside of the particle. As the outside dries, the water becomes saltier and water is drawn from inside the particle bringing more salts with it. Which is why it dries white.

Hope this helps. What we are talking about covers a lot of science. (When I get time I'll address the CEC thing)

Cheers

Paul

[Pup]

This is not by any means a test, as has been conducted by the correspondents of this thread. Here in Western Australia we have a lot of variation in our scheme water.

In many of the Northern suburbs there is a very high incident of salt content in the water. Having said that! it is because what we see is a build up of white lime like scale on the pots and leaves.

While in my suburb it has been tested as the purest scheme water in the Metro area. Now using a very free draining mix.
Both the same, it does still show in the Northern suburbs.

Some growers wash it off as soon as they see it, so there is no big build up, where others who are lazy do not.

Hence, a thread of mine about lime scale removal from pots.
So in my opinion for what it is worth your water has more to do with it, than the mix. I will say, the tap water I tasted when we were in Eorope, was not as nice as home. So I drank the beer or coffee.

Cheers Pup

[Ash]

So I drank the beer or coffee.

Cheers Pup

So I have to share my beer with my bonsai ?
cheers Ash

[bodhidharma]

I read these threads with interest and try to relate to the problems at hand but do not suffer hardly any of these problems. So, of course i wondered why. Not because i am any great Bonsai Maestro for sure. Having given it some deliberation i now know why Firstly i use a very free draining mix and organic fertiliser but the most important thing that i do is irrigate from a very large dam on my property. It would be full of clay particles fish and yabbie poo minerals from the reed beds that the water screeds through and of course unadulterated rain water. It comes from the sky (der) but more importantly leeches through the paddocks which has worms, frogs compost etc. The water must be incredibly live and nutrient laden thereby solving a lot of my problems naturally.

[Bretts]

Hi Paul
"Where under watering" is simply stating that the advice was under the heading of Watering.
Walter makes no mention of flushing the medium only that if you water often then salt will build up. Hence for salt intolerant plants with a medium that needs frequent watering you should use rian water. I have made assumptions here that Walter does flush out his medium as that is what he recommends in other instances.

Maybe what we see as the white buildup is not salt per say but I still think that it makes sense the more often you water and it dries out it has to leave more residue even if most is washed away. I am using the white residue as an example we can see. Maybe actual sodium residue is something we can't see I don't know but when I think about it it makes sense to me that the more often you water and the medium dries in between the more salt build up you will get. If the salt residue is anything like the white residue we see some will not be washed away. It would need to be scrubbed to remove it!

I am sure just adjusting my fertiliser for the hornbeams will make a difference as I know realise the best year I had was when I was using a very weak soil improver instead of a fertiliser.
But when Mr KISS who is in a colder climate than ours states that he has found tap water to cause salt residue buildup in a frequently watered mix to the point it affects salt intolerant hornbeams it makes me consider that it is an issue!
I have also heard Walter say he Waters Hornbeams 3 times a day. Some one did tell me what his water was like but I can't remember. I would love to see if his opinion on this has changed any in the last 10 years.

Hey Pup you say they wash this lime scale off. I have found it does not wash of and wonder what you mean?

[Pup]

Hey Pup you say they wash this lime scale off. I have found it does not wash of and wonder what you mean?[/quote]

If it is a light build up of scale or salt not sure. If it is left to build up not you will not wash it off.
If you get rid of it almost straight away you do not get the build up. Just what those in the areas prone to bad water


Ash, are your trees, not worth a good beer or two

Cheers Pup

[Bretts]

This is what I was suggesting I see this buildup on the pot rim over my terracotta pots and also on the surface of my mix and it does not wash of so why do we believe that just flushing the free drianing mix washes away all the residue?

[Pup]

This is what I was suggesting I see this buildup on the pot rim over my terracotta pots and also on the surface of my mix and it does not wash of so why do we believe that just flushing the free drianing mix washes away all the residue?

Brett Terracota is more absorbant to salts and staining unless it has been treated. Other than that I cannot explain it, what I will do if I remember is next time I am at or see this residue again I will take a picture.

Cheers Pup

[Bretts]

This is what I was suggesting I see this buildup on the pot rim over my terracotta pots and also on the surface of my mix and it does not wash of so why do we believe that just flushing the free drianing mix washes away all the residue?

Brett Terracota is more absorbant to salts and staining unless it has been treated. Other than that I cannot explain it, what I will do if I remember is next time I am at or see this residue again I will take a picture.

Cheers Pup

I use crushed terracotta in my mix and I am thinking hard fired mineral/clay as a general medium as much the same. If the terracotta pot is holding this residue then I gather much the same is going on with the medium inside the terracotta pot

[kcpoole]

Have a read of the article from Walter today on his blog to get his thought on this topic.
No Research to back it up but he does have a bit of experience too to back it up

http://walter-pall-bonsai.blogspot.com/ ... glish.html

Ken

[Bretts]

Thanks KC
Thats pretty well what I had gatherd from his general ramblings. It is great that he has now put it all together in one article. Walter is sometimes accused of making broad statements so thats why I was unsure how to take the advice he gave ten years ago that was specific for hornbeams and the advice he was giving on a broader scale. Had it changed or was this more specific advice?
The mix he was using for hornbeams back then was 20% coarse sand 20% akadama 10% peat moss and 50% humus specificly bark humus.
He now states in this article that sand is not good. He also states normal akadama is no good I can only guess he does not include hard akadama in that?
He has alot of hornbeams so you would think he would mention if they did not like this treatment.
Seems like the perfect chance to ask him about his article 10 years ago and wether it is still relevant to him at all?

[Bretts]

I posted a comment up so will be intresting to see what he says!

Hi Walter
Great to see all this advice in one concise article.
It seems the opportune time to ask a question I have had since reading an old article of yours in Bonsai Today #70.
In this article you state that hornbeams are salt intolerant and if you have a siol mix that needs watering often you should use rain water with them.
This was 10 years ago and although it seemed against what I have read from you recently it seemed to make alot of sense to me as I recently concluded that my leaf margin burn on hornbeams was from salt toxicity. I get edge leaf margin burn on the mature leaves while the new growth is undamaged. I believe I am using a modern mix but realise the year I had almost no margin burn was when I used a very weak fertiliser schedule!
I was planning on following the soil mix advice you gave in that article which would be a more water retentive mix than I usually use but now I am unsure?
I even installed a rain tank so I have fresh water!
Thanks for any help
Brett