Root oxygenation and container choice

Lars Grimm

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Hi All,

I was listening to Bjorn's end of year podcast and he was discussing the different types of containers used for growing pre-bonsai/rough stock (specifically not finished bonsai). He made the comment that wooden containers are the best in terms of providing root oxygenation (I'm paraphrasing here). This got me thinking, as I have heard this statement very frequently from others as well.

When most of us build wooden boxes, we leave big open spaces at the bottom that are covered up with mesh, screen, or some other porous material that keeps the soil in place but allows drainage/aeration. Although wood may be slightly more permeable to air than clay, plastic, metal, etc, it seems as if the material is far less important than the exposure surface area. The top is completely exposed to the air in all containers, but typically a ceramic pot has only a few drainage holes on the bottom which dramatically limits exposure. To me, this suggests that an Anderson flat which is filled with open spaces on the bottom should perform as well or likely even superior to a wooden box in terms of aeration (depending on the wooden box base design) and a pond basket should be the best of all.

There are other reasons to choose a wooden box, such as aesthetics or the ability to customize the size, but it appears as if the material itself is likely a marginal component at best.

Thoughts as always are appreciated.

Sincerely,
Lars
 

Ohmy222

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I like pond baskets the best because the roots generally are so easy to work with. Some only use them for conifers but I think they are as good or better for deciduous. You won't have any circling roots with them. Having said that you will rarely see them in shallow heights and that is the biggest benefit to Anderson flats and grow boxes. I bought several pond baskets that are about 8 in across and only about 3 in tall but never have seen them again. They are perfect for smaller material. If you want a really flaring root base or have really large material then pond baskets aren't viable. I use all three. I am a big fan of Anderson flats but even they are limited in size at 15"x15" which for collected material might be too small. Lastly, i believe wooden grow boxes are better looking if that matters. A good box with stain on it will always look better on your benches than the bland black of pond baskets and anderson flats.
 

Forsoothe!

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Roots get most of their oxygen by cleaving it from H2O. The air spaces in the growing medium provides an avenue for the gasses of decomposition to escape. In the absence of those air spaces such as where water pools in the bottom of a pot, the plant may still have access to enough O, but is poisoned by accumulation of plant decomposition product gases dissolved in the water that can't escape. That is what smells bad in soggy soil.

Pond baskets also provide air pruning.
 

Lars Grimm

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I like pond baskets the best because the roots generally are so easy to work with. Some only use them for conifers but I think they are as good or better for deciduous. You won't have any circling roots with them. Having said that you will rarely see them in shallow heights and that is the biggest benefit to Anderson flats and grow boxes. I bought several pond baskets that are about 8 in across and only about 3 in tall but never have seen them again. They are perfect for smaller material. If you want a really flaring root base or have really large material then pond baskets aren't viable. I use all three. I am a big fan of Anderson flats but even they are limited in size at 15"x15" which for collected material might be too small. Lastly, i believe wooden grow boxes are better looking if that matters. A good box with stain on it will always look better on your benches than the bland black of pond baskets and anderson flats.

I have found the same thing with regards to only small sized pond baskets. Jonas on Bonsai Tonight had an interesting post a while back about how pond baskets may allow the core to dry out and so period dunking is needing.

I really like Anderson flats. The only drawback is that they move a little bit and so I worry about disturbing new root growth if I repot in Spring and have to move trees in and out of cover. I have compensated for this by just placing the filled Anderson flat inside a second one which gives a lot more stability.
 

Lars Grimm

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Roots get most of their oxygen by cleaving it from H2O. The air spaces in the growing medium provides an avenue for the gasses of decomposition to escape. In the absence of those air spaces such as where water pools in the bottom of a pot, the plant may still have access to enough O, but is poisoned by accumulation of plant decomposition product gases dissolved in the water that can't escape. That is what smells bad in soggy soil.

Pond baskets also provide air pruning.

Very informative. Would this argue in favor of a larger particle size drainage layer to provide a zone of air space above the ceramic bottom?
 

coh

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One of the nice things about wooden boxes is they are solid - if you have to move the plant there is no flex so the roots stay intact. I haven't really worked with Anderson flats but being relatively thin plastic I'd be concerned about the soil mass/roots being disturbed when they are moved. Maybe someone who has used them more can comment on how sturdy they are. Same for colanders, some of them flex a fair amount. Once the roots really fill the pot it may not matter, but before that point the movement could play a role (maybe more than any oxygen benefits).

Edit to add - @Lars Grimm just saw your comment about the Anderson flats flexing, missed it the first time through :)
 

Forsoothe!

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No, the old wisdom of a roughage layer in the bottom has been proven to inhibit drainage just above it. Any material that does not compact over time will work fine for the whole profile.
 

Ohmy222

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I should be clear that I have no idea if pond baskets are better for oxygenation of the roots or how they impact health vs other containers. I just like them because the roots grow to the edge of the pond baskets and stop so you get a good mass of fine roots, none of which are circling. So much easier than dealing with coiling roots. They are somewhat flimsy but you should be lifting from the bottom anyway. Also, my Anderson pots hardly nest so I cant double up. The best would surely be a wooden box with mesh sides and bottom but more difficult and pricey to build. Also should point out that anything I have in a pond basket is probably 'too small' for most to bother with building a grow box. I am using them as replacements for 4in and 1-3 gallon pots.
 

Lars Grimm

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No, the old wisdom of a roughage layer in the bottom has been proven to inhibit drainage just above it. Any material that does not compact over time will work fine for the whole profile.

Yes, it inhibits drainage, but shouldn't it improve aeration? I assume they are related, but not definitively mutually exclusive.
 

KLSbonsai

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@Lars Grimm when any soil does not drain well it will become anaerobic. By definition that is the lack of oxygen in the soil. The drainage and oxygen are very closely tied to root and plant health. The balance of water and oxygen is one of the most important to overall plant health. Also anaerobic soils also lead to death of soil biology (fungi, bacteria, nemetode, protozoa).
 

TN_Jim

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In the podcast he also said (from memory, not a quote) that he also uses or promotes use of pond baskets and colanders for growing out trees.

My experience with all three (wood-fashioned box included), is that the box is going to retain more volume water longer, and therefore be the least O2-available among the three over a given comparable time, better or worse (good soil/watering none worse!!?).

Anderson flats do seem floppy (dunno, I’m weary of them), I don’t experience such noticeable movement with my array of thrift store colanders.
 

BuckeyeOne

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Where do you guys get you Anderson flats? I've looked, but can't find them at a reasonable price.
I've gotten quotes from several distributors, but with shipping they just didn't make sense.
I did find exact duplicates that are 15" square and are used for worm farms and more cost effective.
 

KLSbonsai

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Anderson flats are tough for those of us on the east coast. I have only found them from suppliers from Washington, American Bonsai has a similar product that is higher in cost but may be a wash when you figure shipping cost from the west coast.
 

sorce

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Myth myth bo byth.

There's a minimum of 5 "it depends' " to consider with each pot.

That's only the beginning!

Sorce
 

MichaelS

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Very informative. Would this argue in favor of a larger particle size drainage layer to provide a zone of air space above the ceramic bottom?
Yes. But it has nothing to do with drainage
 
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I've gotten quotes from several distributors, but with shipping they just didn't make sense.
I did find exact duplicates that are 15" square and are used for worm farms and more cost effective.
Man, $33 for a pack of two. I just bought some 1/4" hardware fabric. I'll make a wooden frame and then put the fabric on the bottom. Criss-crossing it to make it 1/8" mesh.
 

MichaelS

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Yes, it inhibits drainage, but shouldn't it improve aeration?
Yes. Actual drainage of a media is almost never a problem. Lack of aeration at the bottom of a container can most definitely be. An aeration layer does not alter the amount of water leaving the container for most intents and purposes. Water ''perched'' above the aeration layer is usually unlikely but if it occurs it is not a problem.
 

TyroTinker

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Following a different line of thought, would the wood in a grow box hold any moisture that might be beneficial? Something the plastic containers might not? Or do most wooden grow boxes not have enough surface area, or are they usually sealed?
 
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