Can anyone explain, or link me to, a complete/thorough description of the "salt build-up" problem I so often hear?

[SU2]

I hear about this so often but, upon asking for more info, am left wanting. I've googled and read some articles but am still not getting it (in the context of inorganic soils that get heavy watering- I can understand it in the context of, say, wayyy over-fertilized organic substrates)

Am I way off-base in thinking that I'm not subject to this problem because I do several heavy waterings of inorganic substrates between fertilization? If so then I'm thinking that, on some schedule, I'll do an extra-heavy flushing of my containers (maybe weekly? I feed 24-8-16 at 1tbsp/gallon every third day)

Thanks!!

 

[0soyoung]

Salt build up occurs by two means.

1. high CEC medium
2. evaporation of a 'salty' water

Since our pots have drainage holes, you should read up on Cation Exchange Capacity. Google and then move on to Google Scholar. I'm sure you will find enough that you won't need to buy anything behind a paywall.

 

[BrianBay9]

With modern, mostly inorganic soils I don't think salt build up is really a concern. Inorganic free draining soils tend to have modest CEC necessitating frequent fertilization. They are free draining so they need frequent and complete watering, and the frequent watering takes care of residual fertilizer. The only way I can see a problem is if the quality of your water is so poor that it can't efficiently wash out excess fertilizer. Seems unlikely in most locations.

The only place I get build up is on the OUTSIDE of the pots, where they don't get flushed enough.

 

[Anthony]

Interesting, Brian, our soil is designed to hold fertiliser in weak
solution for several days.
So the stuff can be properly processed by microbes and roots.

You get a mild scuzz around the drainage hole, but nothing to write
Bnut about.

According to Texas edu. Compost feeds in your climate, N for 4
years. Probably 2 in ours.
Good Day
Anthony

 

[BrianBay9]

Interesting, Brian, our soil is designed to hold fertiliser in weak
solution for several days.
So the stuff can be properly processed by microbes and roots.

You get a mild scuzz around the drainage hole, but nothing to write
Bnut about.

According to Texas edu. Compost feeds in your climate, N for 4
years. Probably 2 in ours.
Good Day
Anthony

Yeah, sorry, should have prefaced that by saying I'm using chemical fertilizers for the most part. We did a quick study and found with inorganic substrates, chemical fertilizers completely flush out in 3 or 4 days, watering every day.

 

[Anthony]

Well Brian,

I have to say a big thank you !

!!Thank you !!!

Then there is a good chance if your inorganic substrate takes 3 to 4 days to flush out.
Perhaps out 1/3 strength Moracle Gro lawn fertiliser lasts a week in the compost.[ 12 N.... ]
Would explain the growing results.
Good Day
Anthony

 

[SU2]

Salt build up occurs by two means.

1. high CEC medium
2. evaporation of a 'salty' water

Since our pots have drainage holes, you should read up on Cation Exchange Capacity. Google and then move on to Google Scholar. I'm sure you will find enough that you won't need to buy anything behind a paywall.

I've read as much as I think I'm capable of re CEC, I don't think I'm capable of hitting the point where I can do maths and figure-out what level, if any, salt build-up I have in my containers... But I posted this in a more general sense, I guess I'm wondering if it's of any concern at all in, say, a perlite-only medium? I know that's a bad medium to use but curious about it in terms of salt build-up so I can get a feel for how legitimate/practical a concern it is in the context of our modern, largely-inorganic media (CEC of organics being far higher of course) Would you expect salt build-up in perlite-only if doing a heavy feeding schedule, say 24-8-16 at 1tbsp/gallon every three days?
The CEC of perlite is negligible, scoria/lava is higher but still pales in comparison to organics....DE and akadama seem good middle-of-the-road aggregates IMO....but when using zero, or <5% organics, and half of the remainder is basically 0meq's cec (50/50 DE/perlite-and/or-scoria)

I'm unsure how to gauge my water's salinity, the only stats I have are:

but obviously adding fertilizer salts is the real contributor, I just have trouble picturing perlite-only being able to hold-on to much of anything if it gets 2-3x daily waterings and 1 feed every third day (or every ~8th watering, so 7 flush-outs in-between - my tap-water isn't so great on its own though obviously!) An orchid mix, given this type of feeding, would be what I'd imagine is a textbook-example of 'salt build-up', but isn't the W.Pall idea that there's enough flushing going on that build-up isn't an issue when using properly sized, inorganic substrate?

 

[0soyoung]

I'm suffering some confusion about the idea of 'build up' and what you mean by it.

One could just fill a pot with nothing but fertilizer and stick a plant in it. Every time it is watered, some of the fertilizer is dissolved and drains out with the bottom of the pot. Repeat and eventually, depending on the volume of water and the solubility of the fertilizer, there's nothing but the plant in the pot. In this case, there is no fertilizer build up.

Now let us mix some material with non-zero CEC with the fertilizer in the pot. Here at the beginning we have a high level of fertilizer salts, but the level will decline with repeated waterings, down to whatever level is bound to material particles. The higher the CEC, the more retained fertilizer ions that will only be slowly flushed out by repeated watering. So, one can always throw in too much fertilizer, which has nothing to do with the substrate material, but it will be washed out, down to the level determined by the material CEC with flushing.

If you water with a dissolved or incorporated liquid fertilizer, the water retained will have a certain salt level, namely the level you applied. So, if you keep increasing the concentration in the watering solution, you will get fertilizer build up in the substrate. Switch to undoped water and the retained fert level will decline to that dictated by the substrate CEC.

Would you expect salt build-up in perlite-only if doing a heavy feeding schedule, say 24-8-16 at 1tbsp/gallon every three days?

It depends on how you apply and water, but I think you are 'wasting a lot of fertilizer'. I use Turface MVP (CEC ~ 35) and add Osmocote Plus (time-temp released 15-9-12) at the rate of 1/4 to 1/2 teaspoon per pot gallon every six months. I think my trees are healthy and vigorous and not wanting for more. Maybe I am under-feeding, but you are using about 365 times more fertilizer than I am. Are you seeing fertilizer burn or algae blooms in the path of your run off?

 

[SU2]

I'm suffering some confusion about the idea of 'build up' and what you mean by it.

I'm referring to the oft-quoted warning that too much fertilizer leads to 'salt build-up', something that I was having trouble picturing in a 'modern bonsai substrate' context-

One could just fill a pot with nothing but fertilizer and stick a plant in it. Every time it is watered, some of the fertilizer is dissolved and drains out with the bottom of the pot. Repeat and eventually, depending on the volume of water and the solubility of the fertilizer, there's nothing but the plant in the pot. In this case, there is no fertilizer build up.

Now let us mix some material with non-zero CEC with the fertilizer in the pot. Here at the beginning we have a high level of fertilizer salts, but the level will decline with repeated waterings, down to whatever level is bound to material particles. The higher the CEC, the more retained fertilizer ions that will only be slowly flushed out by repeated watering. So, one can always throw in too much fertilizer, which has nothing to do with the substrate material, but it will be washed out, down to the level determined by the material CEC with flushing.

If you water with a dissolved or incorporated liquid fertilizer, the water retained will have a certain salt level, namely the level you applied. So, if you keep increasing the concentration in the watering solution, you will get fertilizer build up in the substrate. Switch to undoped water and the retained fert level will decline to that dictated by the substrate CEC.

This ^ makes me very happy you've replied!! Ok so here is how I see it (and you can correct me where I'm wrong!), the higher the CEC the more fertilizer salts an aggregate can hold, which it then releases-back (minus whatever it takes to fuel its own decomp.) Where does the fertilizer 'separate' from the salt molecule it was bound with? In reading the way you phrase that, let's say a piece of scoria soaks-up a small amount of your liquid-borne fertilizer-salts, it then releases that back into the substrate- I thought it'd release it back as a fertilizer-salt, it sounds like you're saying that it can become just a salt left in the aggregate....how would that happen? I guess the mechanism you describe sounds to me like it'd result in fertilizer build-up, not 'salt build-up'...

Would it be fair to say that organic aggregates have far higher issues with this (even when sifted/sieved and in the context of a bonsai-mix)? I ask because the only mechanism I can see for the aggregate being more than just 'fertilizer-salt storage' is in the case of organics breaking-down and using the absorbed fertilizer to fuel that, in which case they could use some of the nitro leaving themselves 'saltier' which, if I understand correctly, can lead to bad issues in the context of a substrate getting too-dry to the point where the salt becomes a water-sink against the roots around it and dries them out (a condition that doesn't sound like it'd exist in properly-watered bonsai soil....my top 1/2" may get dry but no more than that, and imagine you'd have to be pretty much bone-dry to have issues of low-level saltiness...

It's not something I've got a good handle on and it sounds like you do, just don't understand why the mechanics of it you describe (which I totally agree w/ ) result in the non-zero cec aggregates being left w/ 'salts' instead of 'fertilizer salt' (the latter being a good thing, the former being a dessicant)

It depends on how you apply and water, but I think you are 'wasting a lot of fertilizer'. I use Turface MVP (CEC ~ 35) and add Osmocote Plus (time-temp released 15-9-12) at the rate of 1/4 to 1/2 teaspoon per pot gallon every six months. I think my trees are healthy and vigorous and not wanting for more. Maybe I am under-feeding, but you are using about 365 times more fertilizer than I am. Are you seeing fertilizer burn or algae blooms in the path of your run off?

Oh in the containers w/ crappy substrate mixes (perlite-only in some cases!) yeah it's a terrible waste, not just fert but water - I re-boxed two trees from last year that had this because, as it started getting hotter here, they'd be wilting by 2p even if they were soaked at 10a!!

And I've seen fert burn in very minor cases here & there (though I can't be sure it's not just heat/sun either, had begun the increased dosage as the sun levels were increasing), but algae for sure, I may've ruined a couple really good & mature trunks that were in these cases because they've got such a strong ring of algae at the substrate surface...have begun a comparison trial using isopropyl/hydro.peroxide/vinegar to treat this, to see which is most effective, but yeah I've got bad problems with this on some of my specimen :/

Are you using that low a dose in a fully inorganic mix? That's sooo low!

My newest mixes (what I used to re-plant the ones that were in perlite or perlite/scoria only) are much heavier in organics up to 20% (at least ~12% bark-chunks in a case of 20% organics), using roughly equal amounts of scoria/perlite/DE to comprise the remainder (thoroughly sifted/sieved to a 1mm minimum, which I retain for the top few inches of large containers or for the very top of smaller ones, ~2mm is the minimum for the remainder / majority of the mix), so far they're holding water real well and everything's looking good (they're also my first boxes to have metal-screened bottoms instead of wood )

 

[0soyoung]

You will either need to refer this to a chemist or dig deeper yourself with the help of Google Scholar - it can get complicated trying to explain all the circumstances involved in your question (plus I always get myself into trouble with "BS chemistry").

Are you using that low a dose in a fully inorganic mix? That's sooo low!

Again, I am using only Turface MVP - a totally inorganic, high-fired clay. My application rate of Osmocote may be soooo low. As I said, while I may be "underfeeding", my trees are healthy and grow vigorously, IMHO. Trees are made from water and thin air --> CO2. Mineral nutrients are just extra stuff for running the machinery.

 

[MichaelS]

It's not something I've got a good handle on and it sounds like you do, just don't understand why the mechanics of it you describe (which I totally agree w/ ) result in the non-zero cec aggregates being left w/ 'salts' instead of 'fertilizer salt' (the latter being a good thing, the former being a dessicant)

It doesn't matter what salts you are talking about. It's the electrical conductivity you need to understand. The higher the ec the higher the chance of plant damage. EC can come from any ''salt'', be it ammonium nitrate or sodium chloride. Some salts are nutrients, some are not, You want to give the least amount of non-nutrient salts so you can give more nutrient salts for the same EC. For example sodium chloride (NaCl) is not a nutrient salt (although plants do use some) so if you keep that down you can add more ammonium sulphate for example. If you have a high NaCl level in your water even before you add fertilizer it will contribute to the final EC of your solution. Some plants - olives for example can tolerate high EC (including NaCl) levels which would damage other plants. Others - azaleas for example, have a very high sensitivity so if you want to fertilize them properly, you will need pretty good water quality. (calcium carbonate is just another salt BTW but not very soluble)
As for salt build up, it's very rare unless you have a high EC water (irrigation water not fertilizer solution) and you allow the medium in the pot to dry too much between watering.
In other words, there is usually no need to worry about it if you follow general fertilizer and watering recommendations. In theory, the CEC of a mix can affect the EC by holding nutrients but in practice we don't feed plants heavily enough for that to be much of an issue. I would say that most people who use a low CEC mix don't feed often enough.

 

[Smoke]

You should pick up my new book "Listening to the bonsai pot fertilizer myth, and why it doesn't apply"

At Amazon

 

[Bonsai Nut]

in the context of inorganic soils that get heavy watering

I am not aware of salt build-up being an issue in this context. In fact, it is one of the arguments for using inorganic soils - allowing fresh water to freely pass through the substrate and prevent salt-buildup.

OUTSIDE OF the context of bonsai and inorganic soils, salt buildup is a real issue here in Southern California because we use irrigated water that is high in sodium, and because we are trying to "save" water the tendency is to not water deeply enough. The combination of salty irrigation water, shallow watering, and no natural rainfall for 9+ months out of the year can cause real problems in lawns and landscape plantings.

 

[Smoke]

I am not aware of salt build-up being an issue in this context. In fact, it is one of the arguments for using inorganic soils - allowing fresh water to freely pass through the substrate and prevent salt-buildup.

OUTSIDE OF the context of bonsai and inorganic soils, salt buildup is a real issue here in Southern California because we use irrigated water that is high in sodium, and because we are trying to "save" water the tendency is to not water deeply enough. The combination of salty irrigation water, shallow watering, and no natural rainfall for 9+ months out of the year can cause real problems in lawns and landscape plantings.

That’s why gypsum should be in everyone’s bonsai mix. There’s a reason farmers till tons into their farms soil.

 

[SU2]

You will either need to refer this to a chemist or dig deeper yourself with the help of Google Scholar - it can get complicated trying to explain all the circumstances involved in your question (plus I always get myself into trouble with "BS chemistry").

For sure! I post here & /r/bonsai for my general stuff but do a ton of googling and post in chemistry boards when I can't figure it out in the aforementioned domains ;D

And 'BS Chemistry'? You??!! Tell them to kick rocks lol, you're totally one of the sharpest prominent posters on this board!

Again, I am using only Turface MVP - a totally inorganic, high-fired clay. My application rate of Osmocote may be soooo low. As I said, while I may be "underfeeding", my trees are healthy and grow vigorously, IMHO. Trees are made from water and thin air --> CO2. Mineral nutrients are just extra stuff for running the machinery.

Can you elaborate on what you mean by "trees are made from water and thin air --> C02"? Am only asking because I'd read an article on nutes yesterday that framed it that way (ie that carbon/hydrogen/oxygen are the structural nutes, then primary nutes as NPK, secondary as CA/Mg+/Su, and micros for the rest, it was the first time I'd read a nutrient break-down in that manner)

And your low osmocote may ultimately give your trees more than my higher-dosage immediate-release products do, in fact I'm not even able to verify that the forms of nutes in my miracle-gro 24-8-16 are in forms that are available for immediate uptake by the roots because, whatever % is not immediately available, is probably 90%+ lost due to the heavy waterings in-between fertilizing days. Am going to be getting a bag of osmocote or something similar (I've got a sweet spot for espoma's products) that I can mix-in with my substrate, plants want to be able to take-up what they want when they want it, putting in extra nitro today and then flushing it for 2-3 days isn't a solid approach IMO (yet it's my standard right now...have top-dressed the espoma granules on some of my better specimen but need a bigger bag, am getting close to 100 trees lol)

[edited-in: and you mean pure turface? I realllllly want to try that stuff, it's like it falls somewhere in-between scoria and diatomite (two things I currently use a lot of), just haven't been able to find it yet :/ ]

 

[SU2]

It doesn't matter what salts you are talking about. It's the electrical conductivity you need to understand. The higher the ec the higher the chance of plant damage. EC can come from any ''salt'', be it ammonium nitrate or sodium chloride. Some salts are nutrients, some are not, You want to give the least amount of non-nutrient salts so you can give more nutrient salts for the same EC. For example sodium chloride (NaCl) is not a nutrient salt (although plants do use some) so if you keep that down you can add more ammonium sulphate for example. If you have a high NaCl level in your water even before you add fertilizer it will contribute to the final EC of your solution. Some plants - olives for example can tolerate high EC (including NaCl) levels which would damage other plants. Others - azaleas for example, have a very high sensitivity so if you want to fertilize them properly, you will need pretty good water quality. (calcium carbonate is just another salt BTW but not very soluble)
As for salt build up, it's very rare unless you have a high EC water (irrigation water not fertilizer solution) and you allow the medium in the pot to dry too much between watering.
In other words, there is usually no need to worry about it if you follow general fertilizer and watering recommendations. In theory, the CEC of a mix can affect the EC by holding nutrients but in practice we don't feed plants heavily enough for that to be much of an issue. I would say that most people who use a low CEC mix don't feed often enough.

Wow thank you! That's been copied into my pH/CEC document (am writing my own book/notes as I go!), will need to read this a couple times (spaced apart) to really absorb it...how bad would you consider my water in terms of EC?

They don't list it but can it be calculated based off the TDS? Also, do you think it'd be overkill/unnecessary to get an EC meter?

I don't allow the medium to dry too-much between waterings (I actually worry that some of my trees have a problem regulating temperature, I'll have stuff starting to wilt in the midday sun even if it got watered 3-4hrs prior, and I mean hose-watered canopy/trunk/substrate....I thought it was poor substrate but I've since re-boxed a couple of the trees in question and put them with ~20% organics and into bigger boxes- no detectable difference, still fast wilting)

In other words, there is usually no need to worry about it if you follow general fertilizer and watering recommendations. In theory, the CEC of a mix can affect the EC by holding nutrients but in practice we don't feed plants heavily enough for that to be much of an issue. I would say that most people who use a low CEC mix don't feed often enough.

Good stuff, precisely what I was hoping to hear What do you consider low CEC? For instance, lately I've been making tropical (bougainvillea) mixes with ~40% diatomite(8822), 25% perlite, 20% scoria/lava (1-5mm), and 15% organics (mostly pine-bark chunks, some sphagnum moss and a pinch of peat on the top / as top dressing), am thinking that this is still well within the realm of 'low cec' right? Max CEC would be epiphytic mixes for orchids if I'm understanding correctly..

Thanks for such a great reply I really appreciate it!!

 

[SU2]

I am not aware of salt build-up being an issue in this context. In fact, it is one of the arguments for using inorganic soils - allowing fresh water to freely pass through the substrate and prevent salt-buildup.

OUTSIDE OF the context of bonsai and inorganic soils, salt buildup is a real issue here in Southern California because we use irrigated water that is high in sodium, and because we are trying to "save" water the tendency is to not water deeply enough. The combination of salty irrigation water, shallow watering, and no natural rainfall for 9+ months out of the year can cause real problems in lawns and landscape plantings.

Good stuff, thanks!!

(and hey, at least that kind of enviro gets the bougies blooming ;D )

 

[0soyoung]

some of my trees have a problem regulating temperature,

Same ole rant:

Buy a cheap meat thermometer probe at you local grocery/hardware store and stick it in the pots, among the roots, am measure what tempertures they are experiencing rather than guessing. Roots stop growing above 95F/35C and are definitely dying above 115F/45C.

Otherwise, it is all about air temperature and relative humidity that you can also monitor with a slightly more expensive device or look up in the report of the local weather on your phone. There also a likely people nearby that participate in the Citizens Weather Observer Program. They make minute by minute data from their station available in .csv files.

 

[SU2]

That’s why gypsum should be in everyone’s bonsai mix. There’s a reason farmers till tons into their farms soil.

I'm reading up on it now but would love to hear your elaboration if you've got a moment! (why you're using it, how much etc etc ;D )

 

[SU2]

Same ole rant:

Buy a cheap meat thermometer probe at you local grocery/hardware store and stick it in the pots, among the roots, am measure what tempertures they are experiencing rather than guessing. Roots stop growing above 95F/35C and are definitely dying above 115F/45C.

Otherwise, it is all about air temperature and relative humidity that you can also monitor with a slightly more expensive device or look up in the report of the local weather on your phone. There also a likely people nearby that participate in the Citizens Weather Observer Program. They make minute by minute data from their station available in .csv files.

Interesting, thanks for this am going to buy a meat thermometer so I can have an idea! But really I just can't see how bougainvilleas would have trouble in this context, I mean I'm barely warm enough to give them the light/heat they want (they're from much closer to the equator than I am), and these are in wooden boxes (light-colored, some level of insulation, etc) so if I measure and find it's too-hot....where do I go from there? I feel like the obvious answer would be 'less light' but these are all in the same spots they grew up in last year when I collected&propagated through the entire spring&summer!