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Akadama (赤玉土, akadamatsuchi, red ball earth) is a naturally occurring, granular clay-like mineral used as soil for bonsai trees and other container-grown plants. It is surface-mined, immediately sifted and bagged, and supplied in various grades: the deeper-mined grade being somewhat harder and more useful in horticulture than the more shallow-mined grades. Akadama may also act as one component of growing medium when combined with other elements such as sand, composted bark, peat, or crushed lava. The colour darkens when moist which can help the grower determine when to water a tree.
While akadama is more costly than alternative soil components, it is prized by many growers for its ability to retain water and nutrients while still providing porosity and free drainage. For all of its qualities, many bonsai growers consider the cost of akadama prohibitive or unnecessary. Still other growers claim that when subjected to cold and wet climates, the granules progressively break down into smaller particles which inhibit drainage, an unwanted characteristic of bonsai soil. This problem can be avoided either by incorporating sand or grit in the soil mix, or by using the deeper-mined, harder grades.
Due to volcanic activity, Japan enjoys rich volcanic resources. After volcanic eruptions, volcanic rocks and pumice accumulate near the volcano. Using these unique resources, Japan has developed rich horticultural products. Akadama and kanuma soils are two representations.
Size and components
Medium particle size is 2-6.5 mm and fine particle size is 1-2 mm.
Akadama is used in the cultivation of plants. It can be used alone or mixed in as an amendment to other soil substrates such as lava rock, pumice, stone, peat moss, bark, etc. It is supplied in various sizes including "Shohin" (less than 1/16 inch), "Small" (1/16 inch to 1/4 inch) and "Medium" (1/4 inch to 1/2 inch). All sizes are suitable for many sorts of potted plants but in particular, a preferred choice for cactus and succulent plants.
- Lewis, Colin. "Mineral Components". Colin Lewis Bonsai Art. Retrieved 2013-06-02.