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Healthy Bonsai From The Ground, Up

© David J. Bockman

If you purchased your bonsai from a garden nursery, roadside vendor, Home Depot or Frank's, or even some of the larger bonsai supply nurseries (New England Bonsai in particular) chances are extremely good that the soil is substandard and will have to be replaced with more suitable material. My observations have been that these types of vendors use a soil high in organic material and particle sizes are too small. Often the tree's roots are badly in need of some pruning as well. Other horror stories would include no drainage holes, various unwanted fauna, and decorative gravel being hot glued to the surface soil - hermetically sealing the tree's root system, ensuring a quick death and money wasted.

Soil components for bonsai culture can be divided into two basic categories: Organic and inorganic material. Each of these can then be broken down into two other categories, particle size and shape. All these factors play a key role in how well your bonsai flourishes under your stewardship.

Inorganic soil components - These will make up the vast majority of the mixture you will wish to use for your bonsai, regardless of the species. If you read books on bonsai you will often see references to such things as sharp river sand, akadama soil, decomposed granite, turkey grit, blasting sand, volcanic soil, and other mysterious-sounding items when describing the perfect soil recipe for bonsai. No doubt all of these items work well, in the right proportions and particle sizes. I use a calcinated (kiln-fired) clay material called Terragreen. It is marketed as a soil amendment or sports field conditioner; one often sees it on baseball infields. Terragreen is actually montmorillonite clay, which is mined in the southern United States. After it is kiln-fired, crushed and screened, a fairly sharp (jagged) particle results that will not break down over time. This is its chief advantage over akadama and volcanic soils - you don't have to keep replacing it, and it can be recycled again and again. Terragreen is almost identical to Turface, which is mined a few miles down the road from the Terragreen people. Essentially they will perform the same.

"Wait a minute, Dave - kiln-fired clay particle? Isn't that just plain old kitty litter?"

Actually, yes and no. Typical inexpensive kitty litter is fired clay, yes, but it is heated to a much lower temperature. That's good for cats, because it will clump together and coalesce around kitty pee, but bad for bonsai because it will do the same with bonsai water. Other hazards would include added ingredients like fragrance and odor-absorbing materials which would harm a bonsai over time. So, one wants a clay particle which is fired quite high - in the case of Terragreen, it almost becomes a ceramic material, creating a particle which is quite long lasting.

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