| Bonsai Soils Revisited by Ken Goebel
(MBS Newsletter Jan.2008)
This revision complements my original soil article found in the Minnesota Bonsai Society Newsletter, April 2007, and contains updated information on the basic soil elements based upon my experiences over the past year. In particular, the specific soil mixes have been adjusted to reduce degradation effects of some of the organic components, which can lead to drainage problems over time. Basic Soil Ingredients As this is an introduction to bonsai soils, only the more common ingredients are reviewed here. Aggregate Clays Kanuma - A mildly acidic clay used primarily for acid-loving plants such as azalea, gardenia, camellia and many conifers. This material comes from the Kanuma area of Japan which is basically the center for growing azalea bonsai. Akadama – Regarded as the best potting medium for bonsai to promote root growth and provide a medium for optimal water and nutrient retention. Akadama is a neutral (not acidic or basic) clay. This volcanic soil component is dug out of old cryptomeria forests of Japan. Turface – Turface is a very porous calcined clay. Each particle is full of tiny holes which absorb water and release it back to the soil slowly. Its pH is essentially neutral. It resists compaction, thereby leaving more room for air in the soil, and promotes better water drainage. Aggregate Rocks Haydite – The rock equivalent of Turface, it is basically shale found along river beds. The aggregate fines are used in soil conditioning. Kiln-fired, the expanded shale is microporous, inert, and essentially pH neutral. Grit – Composed of crushed granite, this is an excellent structural amendment to bonsai potting soil. Unlike clay or expanded rock, crushed granite is dense and solid. It is completely inert, and has sharp edges which encourage fine feeder roots to split into a more tortuous network. Organics The organic components are simply a medium for dispersing nutrients and moisture. They will retain a bit more moisture than the aggregate components, and will also absorb and make available more fertilizer necessary for plant growth. Pine bark and sphagnum peat moss are good for holding moisture. The pine bark keeps its rigidity and provides air-holding pockets in the root zone, which is good for aeration and drainage. The peat moss helps to acidify the soil mix, which is beneficial for pines and azaleas. However, peat moss tends to break down over time, and this can impede soil drainage. Bonsai Soils Everyone has a slightly different idea of what should go into a bonsai soil, but the basic ingredients generally remain the same. And there is no single soil mix that is best for cultivating all bonsai, so I’ll suggest some basic formulas for an effective potting mix. Any usable soil mixture must drain water fairly quickly. Regardless of the components, if the final mixture does not have good drainage and aeration, it will lead to root rot. And the soil should be |
 |