The right bonsai soil mix may not seem as interesting as perhaps shaping your bonsai tree, however it is one of the most critical aspects of your tree’s health and well being.
Enthusiasts may have a slightly differing opinion on what makes a bonsai soil mix. In truth any bonsai soil mix must be prepared to provide several basic components:
- Drainage – water in excess of your trees needs should be able to drain quickly via the pots drainage holes.
- Aeration – the mix needs pieces of a suitable size to allow pockets of air between the soil particles
- Should be neutral pH, i.e. approximately 7. There are many pH test kits available on the market
Bonsai Soil Mix Composition
A general bonsai soil mix should be composed of around 75 percent inert aggregate and 25 percent organic material. The choice of aggregate and organic material becomes is up to the individual.
Aggregate, which may otherwise be known as gravel or small rocks is the largest and a critical component of your bonsai soil mix and comprises on average of 65 to 85 percent of the total soil mix.
- Akadama is hard-baked Japanese clay produced for Bonsai purposes and available some bonsai shops. Akadama is quite expensive resulting in other fired-clay products serving a similar fashion. These are available from a garden centre and are relatively inexpensive. Pumice and small lava rocks display water retention properties similar to fired clay and akadama
- Turface looks similar to Akadama but is not. It is a clay which has been heat treated making it hard to stop it breaking down. It is used on baseball diamonds to increase aeration of the soil. It is also used by Bonsai ( and Orchid) enthusiasts for the same purpose.
- Cat litter is also a choice of many enthusiasts due to its availability and low cost. Some cat litter brands are fired clay products which is fine. Be careful however, some brands of cat litter on the market will contain chemicals which would be detrimental when used in a bonsai soil mix.
- Lava rock is a type igneous rock created by erupting volcanoes. It can be purchased at most garden stores in either red or black. It also looks great on the surface of the soil as a dressing.
This component helps retain moisture, provides small amounts of fertilizer as it decomposes and provides an environment for fungal growth, important for the healthy growth of all plants.
Typical organic components:
- Pine bark because it is inexpensive and is readily available in garden centres
- Sphagnum peat moss – is a common ingredient in soil mixes because it is widely available and is not very expensive. It holds water and air and decomposes slowly.
- Other people will use leaf mulch, old compost, and other plant tissue
- Don’t use materials with too much nutrients such as fresh manure and fresh compost. These may damage the bonsais roots.
The best soil mix
A particular soil mix cannot be singled out as best for bonsai. Variables like your local climate, rainfall, watering patterns, pot size and your tree type can contribute to variations required in a soil mix.
My suggestion when starting out is to buy a pre-made bonsai soil mix from your local nursery or online store. Remember, the best basic bonsai soil mix is 75 percent inert aggregate and 25 percent organic matter.
Happy bonsai gardening!