Bonsai soils are usually a mixture of organic potting compost (Pine Bark or Forest Floor), Akadama, pumice, lava rock in varying amounts.
It is important for the soil have good water retention while also draining well, along with very good aeration. The quality of the soil directly affects the health, size and growth of your tree. One of the worst things you can do to your tree is plant it in regular garden soil. Garden soil hardens when it drys and can often lead to a disadvantage when growing a Bonsai.
Soil mixtures can be purchased here, but given their weight and cost of shipping, you can also easily make your own.
Depending on the type of Bonsai you're growing, here are the general formulas for successful mixtures.
Deciduous Tree (Leafy and looses leafs in the fall)
20% Lava Rock
10% Potting Compost
Coniferous Tree (Evergreen like Juniper, Cedar)
1/3 Lava Rock
If you are not able to check on your Bonsai's moisture levels daily, add more Akadama to the mix.
Given how these soils erode over time, repotting every 2-3 years is required.
Here are some suitable replacements if you cannot find the recommended types of soil.
- Akadama - fine fired or baked clays, some even recommend cat litter as a substitute.
- Pumice - fine crushed aggregates, expanded shale and vermiculite.
- Lava Rock - This can be replaced with fine gravel or you can also look into purchasing a larger lava rock at a hardware or gardening centre and crushing it.
One of the best and easiest ways to fertilize your Bonsai, is to add a liquid fertilizer mix when water your Bonsai's once a month during the spring/summer. If your Bonsai looses leaves in the winter there is no need to fertilize it then. If you have a coniferous tree, fertilizing the tree once in the beginning of winter and once in the middle of winter should be sufficient.