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Raised Grow Beds For Bonsai

© David J. Bockman

This week I would like to recount for you a series of letters exchanged between myself and a bonsai enthusiast in Texas. This gentleman wants to develop bonsai himself using seedlings and nursery stock. One very efficient method is the use of a grow bed, a raised, shallow bed in which the tree or seedling is planted, with the goal of rapidly fattening the trunk in a relatively short amount of time (like three years instead of thirty!)

> I'm in the initial stages of building/installing growing beds in my yard.
>Having recalled a few posts directed to you in the past concerning this, I
>have a few questions that maybe you can help me with. My ideas on this may
>not be feasible so I'd like to pass 'em by you for confirmation or
>disagreement (please warn me of potential mistakes).

No problem!

Before I address your specifics, I'll digress a bit and try to fill you in on my feelings over-all on raised beds.

First, it's important to know beforehand the purpose for a grow bed you're designing. The most obvious reasons are controlled environment and good drainage, but of equal if not superior importance is that the grow bed quickly and efficiently sets the basic trunk structure within the first four to eight years of growth. This means it should be designed in such a way as to promote maximum root flare and trunk taper, and for that there is only one solution: shallow beds that allow for only lateral root growth and shallow, bonsai-friendly root systems close in to the trunk. When I write shallow I mean no more than ten inches deep. By effectively channeling the direction the roots will travel to lateral, you decrease substantially the amount of time needed to create extraordinarily flared trunks, especially in the case of Beech, Maple, Hornbeam, and Elm. That lateral spread can be assisted even more by placing a small plate or tile directly beneath the trunk of the tree as you plant them in.

In my opinion, deep raised beds are kind of an oxymoron: If I wanted a deep planting for whatever reason horticultural I would just dig a three foot hole and plant the tree in, using equal parts rotted manure, peat, sand, and perhaps good loam or some other rich organic. Drainage isn't an issue with field grown stock, unless the site were really poorly situated. For these reasons I feel your beds might be too deep by more than half-- the trees won't benefit from the extra space.

>The decision on the soil medium is where I need the

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