Using the right soil mixture for your Bonsai trees is crucial. Soil is important to supply your trees with nutrients, but it also needs to drain properly, provide enough aeration and retain water. Though most (online) Bonsai shops sell ready-mixed soils, doing this yourself will save money and enables you to adjust mixtures per tree-species.

The quality of soil used directly affects the health and vigor of your tree. It is our experience that unhealthy trees, that lack vigor, are very often planted in a poor (often organic) bonsai soil. Or worse; planted in normal garden soil. Such soil easily hardens when it gets dry, which give no advantage to the growth of bonsai, in fact, it is very harmful to the tree.

There are a number of qualities that are required in a good soil mix

  • Good water-retention. The soil needs to be able to hold and retain sufficient quantities of water to supply moisture to the bonsai between each watering.
  • Good drainage. Excess water must be able to drain immediately from the pot. Soils lacking good drainage are too water retentive, lack aeration and are liable to a build up of salts. Too much water-retention will also cause the roots to rot, killing the tree.
  • Good aeration. The particles used in a bonsai mix should be of sufficient size to allow tiny gaps or air pockets between each particle. Beside the need of oxygen for the roots, it is also important to let the good bacteria and mycorrhizae intact, so the processing of food will take place before being absorbed by the root-hairs and send to the leaves for photosynthesis.

A particle-based, well-structured inorganic soil allows fast drainage of water and allows fresh air to continually enter the soil. A compacted organic soil that lacks any structure also lacks aeration and drainage and this can lead to ill health in the roots and tree and root rot.

Organic or Inorganic Soils

Soil mixes are described as being either organic or inorganic.

  • Dead plant matters such as peat or leaf-litter or bark are described as being organic soil components.
  • Inorganic soil mixes contain little to no organic matter such, for example volcanic lava, calcite (baked) or fired clays.

Recommended Bonsai soil mixtures

Bonsai soil components

The most important components for any bonsai soil mixture are Akadama, organic potting compost and fine gravel (grit).

  • Akadama is hard-baked Japanese clay, specifically produced for Bonsai purposes and available at all (online) Bonsai shops. It needs to be sifted before using it. Keep in mind that after about 2 years akadama starts to break down, significantly reducing aeration. This means that regular repotting is required. Akadama is rather expensive and is therefore sometimes substituted with similar fired/baked clays that are easily available in any garden center. Even cat-litter can be used as a substitute.
  • Organic potting compost includes peat moss, perlite and sand. It has several disadvantages (it retains much water and doesn’t aerate/drain very well), but as part of a mixture it can be used perfectly well.
  • Fine gravel / grit is of great importance to create a well draining and aerated bonsai soil. It is also used as a bottom layer in Bonsai pots to enhance drainage a bit further.