Most plants can survive for a while with their roots growing
in almost anything . From pure gravel to nothing but water, from clay to rotting tree stumps. But to really thrive for
year after year, they need a good balanced growing medium.
Most commercial bonsai soils contain 'fillers', such as
hyalite, large particles of grit or excessive amounts of turface - all of which take up space that could otherwise be colonized
by the roots. They also often contain poor organic material such as dried and sterilized bark chips or dusty peat-based potting
composts. The bark chips remain inert and impenetrable by roots for years, and when they finally begin to decompose they leach
nitrogen from the soil, robbing the tree of a valuable nutrient. The peat-based composts rapidly break down into dust, which
compacts, clogs the micro-pockets in the soil and causes poor drainage and finally root decay.
My bonsai soil blends are based on over thirty years' experience
and close observation of how different species perform with various soils. Every ingredient is selected to perform a specific
function and blended with the others to a formula that suits each species group.
Akadama: Japanese clay-like
granular mineral that permits roots to grow through the particles, thus maximizing available space in the pot for root growth.
Calcined clay: Used only
in relatively small amounts, calcined clay absorbs vast amounts of water and provides a 'buffer' which adsorbs nutrients for
release later as required by the roots.
Crushed lava: As well as
absorbing large amounts of water, the pore spaces in each granule are large enough to allow roots to penetrate. Lava also
contains many available minerals important for healthy plants
Grit: The grit I use is finer
than in most other commercial bonsai soils. Finer grit means more spaces between the particles and a greater surface area
to retain a film of moisture, which in turn leads to more fine root growth.
Secret ingredients: Yes,
there are some! Among them are a prepared organic material that is a proven stimulant for root growth and slow to break down
(3-5 years), and a range of trace elements or micro-nutrients that are essential to healthy plant growth.
Colin Lewis's Deciduous Blend
Colin Lewis's Conifer Blend
Colin Lewis's Pine Blend