Why does general purpose potting soil cause root rot?

Bon Sai

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Hello,

It's not about bonsais but trees in general. I have all kinds of trees, some purchased, some planted by me from seed or cutting, etc. Most aren't for bonsai. The purchased ones which I haven't transplanted I can water as much as I want to with no problems, and I have to water almost ever day in summer because it's hot and windy, but several of the ones I have planted myself have clear signs of root rot. I know the problem is the soil, but I don't know what to do about it. I would need the mix tree nurseries use, if anybody can tell me.

Thanks in advance.
 

leatherback

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Hm. That was a bit short.
The balance between air / substrate / water in the soil determines whether roots get enough air to breath or wether they proverbially drown.

Regular potting soil is often of poor quality and compacts a lot. I find that there are massive differences in different types of potting soil. The more it compacts, the less air remains.

Furthermore, professional nurseries typically do not increase pot sizes a lot: Most of the rootball is dominated by roots, rather than wet soggy soil: It dries out faster.
 

Bon Sai

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So, should I buy another kind of soil? More specialized? Maybe just add coco coir or some other stuff to regular potting soil?

I've also thought of protecting the surface of the pots with something like straw to limit evaporation so I don't have to water so often.
 
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TN_Jim

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Primary ingredient if not the only ingredient (sometimes -species dependent) I see in nursery trees is pine fines. In bagged form this would be the equivalent to a pine bark soil conditioner. Often there is a much lesser degree of peat, vermiculite, and perlite or pumice. As in the pines are the flour in the cake, the other just some sugar, salt, vanilla etc. for flavor.

Potting soil, the flour is typically/primarily peat -very water retentive, as in a peat bog. Very water retentive does not translate to being porous or allowing for requisite oxygen availability tree roots need in pots. Also, potting soil often contains perlite for some added aeration, but this (unlike pumice) will eventually break down over time from ongoing freeze/thaw cycles.

Here’s some pine fines I pulled off the top of a nursery pot:
A9488A30-BAC9-49E1-B27B-DB34C3B42817.jpeg
 

MrWunderful

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Research “inorganic bonsai soil”. Some of the best bonsai soil in the world is grown in it, and the variations discussed here and elsewhere should be available in your area in one form or the other.

I grow most of my container plants in it and also have it as a huge portion of my growing beds for pre-bonsai and vegetables.
 

Firstflush

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You can spend a little bit more money on good potting soil. G&B Blue Ribbon is good stuff in the medium price range.
Not for bonsai but you can make your own for an all purpose mix. 1/3 perlite, 1/3 peat moss, 1/3 compost with some worm castings. Substitute some coir for peat moss as it doesn’t break down quickly and is more sustainable.
 

Potawatomi13

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So, should I buy another kind of soil? More specialized? Maybe just add coco coir or some other stuff to regular potting soil?

I've also thought of protecting the surface of the pots with something like straw to limit evaporation so I don't have to water so often.

Soil trees roots must grow into outside of planting hole is likely problem. Does IT drain well? Too much clay or sand? Soil in planting HOLE is only beginning effort;). Nursery should be able to say what kind of soils each prefers or needs.
 

ConorDash

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Yeah Id say its not the soil. Nurseries grow trees around the world in this nursey potting soil, we could grow bonsai in it too. It may be the most ideal but its not impossible or bad.
It'll be watering habits I think, simply staying too wet and rotting the roots. My opinion.
 

BobbyLane

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has the OP stated what species he's growing. he's in the med where most native trees prefer it on the dry side and free draining. olives and pomegranates for eg wont like it in potting soil for sustained periods. they may grow well in the nursery mix for a time but they wont 'thrive'.
 

rockm

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Hello,

It's not about bonsais but trees in general. I have all kinds of trees, some purchased, some planted by me from seed or cutting, etc. Most aren't for bonsai. The purchased ones which I haven't transplanted I can water as much as I want to with no problems, and I have to water almost ever day in summer because it's hot and windy, but several of the ones I have planted myself have clear signs of root rot. I know the problem is the soil, but I don't know what to do about it. I would need the mix tree nurseries use, if anybody can tell me.

Thanks in advance.
Nurseries use what they use not because it's a great growing medium, but because it straddles the financial/horticultural requirement line. It is not meant as a permanent solution. Nursery trees in containers are meant to be bought and planted in the ground. The soil used is lightweight and cheap--which are the primary reasons nurseries use it. It doesn't last and isn't meant to. It breaks down and clogs.

Bonsai soil is more durable with components that break down more slowly (if at all) and provide better gas and moisture exchange.

Don't make the mistake of using potting soil "because nurseries use it. They're not using it because its great stuff. They're using it because it doesn't cost much and is adequate for a limited period.
 

xray360

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Nursery trees use a good amount of pine bark with peat, and sand mostly. Drainage is important with most trees, and evergreens. Nursery mixes drain well when fresh but after a couple years they'll break down and stay too wet. By that time though the tree roots usually fill up the pot.

General potting soil is mostly for annuals which last one season. General potting soil has a lot of organic fines that stay wet for a long time which most trees, and evergreens don't like. Depending on the trees, the soil needs to dry out between watering. Not bone dry but a little moisture left. If they are constantly wet the roots wont grow and begin to rot. You can amend potting soil by adding more perlite/pumice/grit or what ever is available to give it better drainage. You can also sift the fines out with a screen to allow it to drain better.
 

ConorDash

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Anything where intelligence is no longer needed for succes fits me perfectly!
Substituting intelligent watering habits for barren inorganic media sounds good to me.

:p ;)

Yeah I was gonna say, the more I can remove the variables of watering, timings, weather, humidity in the air, whether it rained, how hard did it rain, did I eat a full breakfast, did I blow my nose, 3 or 4 times today, etc... the better!
Use a modern substrate, akadama, pumice, lava, etc, to remove variables and possibilities of problems, right? :). Still need some sense... which I am still working on... but less!
 

Forsoothe!

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Nursery trees use a good amount of pine bark with peat, and sand mostly. Drainage is important with most trees, and evergreens. Nursery mixes drain well when fresh but after a couple years they'll break down and stay too wet. By that time though the tree roots usually fill up the pot.

General potting soil is mostly for annuals which last one season. General potting soil has a lot of organic fines that stay wet for a long time which most trees, and evergreens don't like. Depending on the trees, the soil needs to dry out between watering. Not bone dry but a little moisture left. If they are constantly wet the roots wont grow and begin to rot. You can amend potting soil by adding more perlite/pumice/grit or what ever is available to give it better drainage. You can also sift the fines out with a screen to allow it to drain better.
Or you could even make the extraordinary adjustment of only watering the plants when they need it. This is very difficult and stupid people can't make this wild and crazy move on their own. Trust me, it's true.
 

Bnana

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I would love to, but I do not control the rain. I regularly have weeks without watering. With a less draining soil that would mean overwatered plants.
My trees are not under a cover obviously
 

Forsoothe!

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Sometimes I forget that I live in plant heaven where it rains periodically, the winds rarely blow more than 25 mph, it almost never gets up to 95°F or down below zero. Thank you, God.
 

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