Akadama is a granular volcanic clay-like (although it is not clay) mineral which occurs naturally in Japan. It has been extensively used by Japanese gardeners and bonsai artists for many centuries as a growing medium for bonsai trees and other container-grown plants.
It is mined from the surface of the ground, after which it is graded and packaged. Unlike LECA it is not fired at high temperatures however when it is mined from greater depths it tends to be harder or it might be slightly baked. It has many unique qualities, one of which is that when it is wet it has a darker colour so indicates when watering is needed
Akadama is unique as a growing medium and is sought after due to its ability for water retention and nutrients due to its high CEC value. However at the same time it provides porosity and free drainage.
Akadama can be combined with other elements such as crushed stone, composted bark, peat, or for best effect use pumice.
Here are a few recipes from leading international bonsai practitioners:
1 part pumice, 1 part lava, 1 part akadama, 1 handful decomposed granite and 1 handful horticultural charcoal.
Akadama, lava rock, and pumice. Use a 1:1:1 ratio respectively for conifers and a 2:1:1 ratio respectively for deciduous and broadleaf evergreen species.
2 parts akadama, 1 part hyuga (Japanese pumice) and 1 part coarse river sand.
Akadama, Double Red Line Brand
Suited to mame, shohin and general bonsai growing mixes. Available in 2L bag, 5L bag and 10L bucket.
Suitable for drainage layers and for medium to large bonsai. Available in 2L bag, 5L bag and 10L bucket.