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Bonsai Substrates by Averil Stanley

As you have seen, the 4 presenters each had their own tried and tested ‘recipe’ for their bonsai potting mixture and each individual mix worked for them – according to the micro-climate in their bonsai gardens, orientation, full sun, semi-shaded or bush house location, life style demands etc. There is NO right or wrong bonsai mix – just a mix that works for you, and of course the availability and opportunity to purchase the ingredients.

All four presenters, Albert Garcia, Michael Clark, Steve Turner and Averil Stanley all had different recipes and ingredient favourites. Averil has supplied what she and Bob use on their Bonsai and is detailed below.

Bonsai Potting Mix (Substrate)

Firstly, using the right potting mix (substrate) for your Bonsai trees is crucial.

It must:-

  • Supply your bonsai with nutrients –the plant roots (through its very fine root-hairs) take up water and mineral nutrients.
  • Drain properly to avoid root rot – excess water must drain immediately from the bonsai container after watering. Substrates with bad drainage are too water retentive, lack aeration and susceptible to a build-up of harmful salts. Too little drainage material will cause the roots to rot.
  • Provide aeration – The particles used in a Bonsai mix should be of sufficient size to allow tiny gaps (air pockets) between each particle. This supplies oxygen to the roots, and allow the formation of good bacteria and mycorrhizae – so the tree can absorb nutrients by the root-hairs and send to the leaves for photosynthesis
  • Retain water – must be able to hold and retain sufficient water to supply moisture to the Bonsai between watering

A particle-based well-structured inorganic substrate will allow fast drainage of water allowing fresh air to continually enter the substrate.

The following is a list of readily available materials suitable for bonsai substrate.


Pumice rock is formed from cooled and hardened lava. Formation takes place when highly pressurized, super-heated molten rock, with its incorporated water and gases, violently erupts to the surface during volcanic explosions.

The horticulture industry makes use of the porous structure of pumice to aerate soils and increase the water retention property of dense soils, as well as utilizing the rock to serve as a growing medium in “soilless” hydroponics crop. It is also multi-faceted and helps to ramify fine feeder roots. Lightweight. 3-5mm in size


It is used in the bonsai substrate to promote faster root growth and gives quick anchorage to young roots. The mixture helps retain air; plant food and moisture – releasing them as the plant requires them. The addition of Vermiculite to our bonsai substrate creates air channels and allows the substrate to breathe, which encourages and maintains vigorous root growth.

Pine Bark Fines

From pine plantations of Pinus radiate or Pinus elliotti fines. Must be composed and aged to avoid nitrogen drawdown from bonsai plant as the pine bark breaks down. Retains moisture and a general soil conditioner. Must be sieved to remove dust and large particles – which can be used as top dressing for garden beds or orchid culture. 3-5mm in size

Sphagnum Moss

Sphagnum Moss is the living moss in a sphagnum bog that floats to the top of the bog.
Sphagnum moss is added to our bonsai substrate – particularly in times of drought – to prevent the mix from drying out as it is highly moisture retentive. It absorbs liquids about 3 times faster; retains liquids better; distribute liquids more uniformly throughout their mass; and promotes the formation of feeder roots. It has a neutral pH and acts as an insulating material and inhibits the growth of bacteria and fungi. Use as fines in the substrate – or placed on the soil surface of newly potted bonsai.

Cow Manure

(must be aged and well-rotted – with no strong odour)
Used as an added ingredient to bonsai substrate as a moisture retention agent, and to provide a limited supply of nutrients. Cow Manure is used fully composted, therefore low in odour; provides excellent amounts of organic matter and nutrient into the mix; is a great retain of moisture; improves soil structure; is environmentally friendly and promotes plant growth in natural organic way. Sieve to remove fine dust particles and (sometimes) stones

Shredded Coconut Fibre

Sold in compressed bricks which need to be immersed in water to expand, ready for use.
An excellent replacement for peat. Available from plant nurseries.

Horticultural Charcoal (Wood Ash)

Used as a soil conditioner, allows the plant to utilise nutrients, acts to deter bacteria and fungi and prevents the substrate from becoming too acid. (regulates the pH level of the mix) 5-7 mm



The Mix

We make a ‘generic’ substrate mix usually consisting of the following

  • 70% decomposed granite (or its equivalent, scoria, pumice)
  • 10% zeolite
  • 20% Pine Bark Mini Nuggets.
  • Handful of charcoal per pot on top of the drainage layer.
  • Handful of finely shredded sphagnum moss
  • Handful of well-rotted cow manure

This is a coarse and chunky mix that waters well but does not stay too wet. We always add Osmocote to this mix at potting time and fertilise well with liquid fertilisers like Power Feed or Nitrosol and Seasol at their recommended doses.

Note that in the ingredient descriptions, preferred grain, particle size was suggested, and does require some time in sifting.

Note that sifting the soil separate the particles by size – and small particles and dust that impede drainage are discarded.
Note that Sifting bonsai soil serves two purposes. It can be used to separate particles that are too small to use in bonsai mix, and it can separate particles by size.

Bonsai sieves are available for the purpose, or you can build your own. A fine mesh will quickly sift out dust and tiny particles that impede drainage. Larger screens will separate soil by size. In general, smaller particles are used for smaller bonsai and larger particles are used for larger bonsai.