Quick answer: a practical all-purpose bonsai mix starts with equal particle sizes and a balance of Akadama, pumice and scoria. Use the recipes below as starting points—not fixed rules—then adjust for your tree, pot depth, climate and watering routine.
A dependable starting mix
For many established bonsai in Australian conditions, begin with:
- 40% Akadama for moisture buffering and root development
- 30% pumice for aeration and useful water storage
- 30% scoria or lava rock for durable structure and drainage
This is a baseline. A grower in hot inland conditions may need more water retention; a grower with high rainfall, deep pots or limited winter drying may need a more open mineral mix.
Akadama mix ratios by tree type
| Tree or use | Starting ratio | Why |
|---|---|---|
| Japanese maples, elms and deciduous refinement | 50% Akadama, 25% pumice, 25% scoria | Balances fine-root development with dependable drainage |
| Pines and junipers | 33% Akadama, 33% pumice, 34% scoria | Creates an open, durable structure for roots that dislike stagnant conditions |
| Ficus and tropical bonsai | 40% Akadama, 30% pumice, 20% fine bark, 10% charcoal | Adds some organic moisture buffering while retaining air space |
| Shohin and mame bonsai | 60% fine Akadama, 20% pumice, 20% fine scoria | Supports even moisture in a small, shallow root volume |
| Young trees in development | 30% Akadama, 35% pumice, 35% scoria | Encourages vigorous roots and reduces the cost of filling larger training pots |
| Moisture-loving species | 50–60% Akadama with pumice and scoria making up the balance | Increases moisture buffering without abandoning mineral structure |
These ratios assume screened particles of similar size. Mixing fine Akadama with very coarse pumice can create uneven water movement and allow fines to settle into the gaps.
Choose particle size before choosing a ratio
- 1–3mm: shohin, mame, seedlings, propagation, shallow pots and fine root systems.
- 3–6mm: medium and large bonsai, deeper training pots and trees that need a more open mix.
Akadama Double Line is the main Harwood’s range and includes both 1–3mm and 3–6mm grades. For a dedicated fine-grade option, Akadama Tsuti 1–3mm is suited to shohin, mame, propagation and fine top dressing.
Adjusting an Akadama mix for Australian climates
Hot, dry and inland conditions
Increase Akadama by about 10 percentage points and reduce the coarsest aggregate by the same amount. Use mulch or shade management where appropriate and check small pots more than once during extreme heat. Do not compensate for an unsuitable pot position by making the mix dense.
Warm, humid and coastal conditions
Reduce Akadama by about 10 percentage points and increase pumice or scoria. Keep particles consistent, protect pots from prolonged rain where possible and avoid leaving water-filled trays under bonsai.
Cool winters or high rainfall
Prioritise drainage, airflow and pot angle. A mix that performs well in summer can remain wet too long when growth slows. Coarser particles and a little less Akadama may be appropriate, especially in deep containers.
Hot summers with reliable daily watering
You can use a more open mix than a grower who cannot water consistently. Watering availability is part of the recipe: the “best” soil is one you can manage safely through the hottest and wettest parts of the year.
Ratios by pot size and development stage
Shallow display pots dry quickly and hold little margin for error. Use uniform smaller particles and test drainage before the tree enters summer. Large training pots can stay wet in the centre, so use coarser, durable aggregates and avoid a fine layer at the bottom. Recently collected or recovering trees often need maximum aeration and stability; follow species-specific advice and avoid aggressive root work.
How to mix bonsai soil evenly
- Sieve each ingredient separately. Remove dust and particles outside your chosen range.
- Measure by volume. Use the same scoop for each ingredient so the ratio is repeatable.
- Mix dry. Turn the ingredients until colour and particle distribution are even.
- Prepare the pot. Fit drainage mesh and tie-down wire before adding soil.
- Work soil around the roots. Use a chopstick carefully to remove large air pockets without crushing particles.
- Water thoroughly. Continue until water runs clear from the drainage holes.
Should Akadama be used on its own?
Pure Akadama can work in some controlled bonsai systems, but it asks the grower to manage watering, fertilising and particle breakdown closely. Mixed mineral media provide a wider safety margin for many Australian growers. Pumice and scoria maintain structure while Akadama supplies moisture buffering and a root-friendly texture.
When to change the mix
Do not repot only because a fixed number of years has passed. Check the whole system:
- Water sits on the surface or drains much more slowly than it used to.
- Particles have broken into fines and pore space is disappearing.
- Roots have filled the pot and watering has become difficult.
- The tree’s health, growth stage or styling plan requires root work.
Repot at the appropriate season for the species. A declining drainage rate is useful evidence, but it does not justify unsafe out-of-season root work.
Common mixing mistakes
- Combining mismatched particle sizes: fines settle between large particles and undo the intended airflow.
- Adding a “drainage layer”: a coarse layer under a fine mix can create a perched water zone rather than better drainage.
- Copying a Japanese or overseas recipe unchanged: climate, pot depth and watering frequency may be different.
- Using percentages without screening: a measured ratio is meaningless if one ingredient is mostly dust.
- Ignoring fertiliser: mineral structure does not replace a suitable feeding program.
Build your Akadama bonsai mix
Start with Double Line Akadama in 1–3mm or 3–6mm, add screened pumice and scoria, and choose the ratio closest to your tree and climate. Browse the bonsai soils collection for related ingredients.
If you need background on origin, particle grades and choosing between Double Line and Tsuti, read What is Akadama soil? The Australian buyer’s guide.
