Bonsai Soils

Anne Spencer

Good soils should hold bonsai up and be heavy enough to sift down among the roots (not fluffy). Nutrients, water and air should be available in a good bonsai soil. The dust should be sifted out of any ingredient you use. Bonsai soils must be dry when applied.

There are as many good soils as there are successful bonsai growers. Whether or not a given soil works depends on climate, environment, weather, light, wind, shelter, watering and fertilizing habits of the grower, and variety of plant, as well as the soil type, texture and size of the soil ingredients, and the pot's depths. All these are interrelated. The challenge is to coordinate them all so it works. Choose one that works for you. Experiment. If you have to be at work in the hot time of the summer, will your soil stay damp enough to keep your bonsai alive?

The following are successful mixes in Western Oregon:

David DeGroot uses 40% bark, 20% each of 1/16"' inch crushed rock (filter sand/bridge topping), crushed red lava, and fired clay (Turface/Profile) (Dust sifted out of all ingredients)

Alan Taft uses 1/3 crushed red lava (dust sifted out), 1/3 washed mason sand (dust sifted out), and 1/3 NineB mix from ProGrow (Wilsonville, OR) (This is mostly fir bark, pumice, a small amount of peat, and compost.)

Anne Spencer uses -fir or hemlock bark, fired clay (Profile), small crushed limestone rock, akadama (from Japan), and crushed red lava, with dust and too big pieces sifted out of all ingredients. I like bridge topping (crushed gray rock), too. The formula varies, depending on the needs of the plant. Limestone isn't used on acid loving plants. Less bark is used on plants that need better drainage, etc..

Boon Maniditivipart uses a basic mix of 1/3 akadama, 1/3 crushed red lava, and 1/3 pumice, with a bit of agricultural charcoal, and a bit of crushed granite added in. He uses this for all his bonsai, conifer, evergreen, or deciduous. 

Screens are used to do the sifting. Window sized screen (1/16 inch) sifts out the dust. Use 1-1/4 inch screen to sift out the big stuff. Large plants can handle larger granules. Very small plants need small granules.