The tool bench
Pick your species, measure your pot, and get the akadama–pumice–lava split plus how much of each to buy.
setting up the bench…
After the math
The quantities are loose, dry volume — what you'd scoop, not what you'd pack down. Buy the next bag size up from each number. Leftover mix keeps for years in a dry bucket, and you'll use it: repotting comes back around every two or three springs.
Mix the components dry in a tub, then sift the whole batch over window screen. That step matters more than the ratio — fines settle between particles and turn a fast-draining mix into pudding.
If the numbers look small, they are. A 10 × 7 × 2.5-inch pot holds about two dry quarts. Shallow pots are the whole point.
No black box
Every rule this tool applies, in the open:
None of this is proprietary. These are the ratios growers have argued about for decades, and the disagreements all live within ±10%. What actually matters is that every particle drains fast and holds a little water — get that right and the exact split is taste.
The care sheet version
| Tree type | Akadama | Pumice | Lava | When to use it |
|---|---|---|---|---|
| Conifer | 33% | 33% | 33% | Junipers, cedars, hinoki. Airy and lean — conifer roots hate wet feet. |
| Deciduous | 50% | 25% | 25% | Maples, elms, hornbeams. More water for trees that drink hard through the growing season. |
| Tropical & indoor | 40% | 30% | 30% | Ficus, Fukien tea, money tree. Steady moisture for heated indoor air; pine bark fines can stand in for part of the akadama. |
| Wet-lovers | 50% | 25% | 25% | Bald cypress, larch, willow, wisteria. Swamp and waterside trees — the extra akadama keeps their feet damp on purpose. |
| Succulents | 25% | 50% | 25% | Jade, dwarf jade, desert rose. The plant stores its own water — the pot shouldn't. No climate shift applies. |
| Lean & fast | 33% | 33% | 33% | Bougainvillea, olive, rosemary, black and white pine. Their care sheets say fast-draining, lean, or gritty — rich mixes rot them. |
| Flowering & broadleaf | 40% | 30% | 30% | Crabapple, pomegranate, podocarpus — everything the rows above don't claim. Balanced, on the dry side of middle. |
| Azalea & satsuki | — | — | — | The exception: straight kanuma, an acidic Japanese pumice (pH 4.5–5.5). No blend at all. |
Before you buy
The calculator gives you quarts; bags are sold in liters and vague “small/large.” Here's the translation, with honest price ranges as of this writing — prices drift, ratios don't.
| Component | Common bag | ≈ Dry quarts | Worth knowing |
|---|---|---|---|
| Akadama | 14 L | ~15 qt | Usually $25–45 shipped. 'Hard' or double-line brands survive freeze-thaw longer. |
| Pumice | 1.5–2 gal | 6–8 qt | Horticultural pumice is the cheap workhorse — garden suppliers beat bonsai shops on price. |
| Lava rock | 1.5–2 gal | 6–8 qt | Sold as 'cinder' in the West. Rinse the red dust before mixing. |
| Kanuma | 14 L | ~15 qt | Azaleas only. Crushes easily — don't stack heavy bags on it. |
| Calcined clay (budget) | 50 lb | ~25 qt | NAPA 8822 or Turface. A fraction of akadama's price at ~$12–18 — the budget toggle above does the swap math. |
The sieve stack
Particle size sets the air-to-water balance as much as the recipe does. Sift dry soil through kitchen or bonsai sieves and keep the band that matches your pot; the dust that falls through the finest screen goes to the garden, never the bonsai pot.
| Pot | Particle band | Why |
|---|---|---|
| Shohin / under 6″ | 2–4 mm (1/16–5/32″) | Small pots dry fast; finer particles hold enough water to survive a summer day. |
| Standard 6–12″ | 3–6 mm (1/8–1/4″) | The default band — what most bagged bonsai soil is screened to. |
| Large / over 12″ | 6–9 mm (1/4–3/8″) | Deep soil columns drain slower; coarser particles keep air in the bottom third. |
More from the bench
Your species
pick a species (or a tree type) and measure your pot — the mix appears here
