Bonsai Soil: What to Buy, What to Mix, and What It Costs

Once you know why bonsai soil has to be coarse and free-draining, the next question is purely practical: do you buy a ready-made bag or mix your own, and what should either cost? This guide covers what is actually in the commercial mixes, three recipes worth using, how much you need per pot, and the label warnings that mean walk away.

# Bonsai Soil: What to Buy, What to Mix, and What It Costs

Bagged mixes vs mixing your own

For one or two trees, a ready-made bag is the sensible choice. You will pay more per litre, but you avoid buying three separate components in quantities far larger than you need, and a decent commercial mix is vastly better than anything you can improvise from garden centre stock.

The moment you own four or five trees, the maths flips. Components bought individually cost roughly half as much per litre, and — more importantly — mixing your own lets you vary the ratio by species, which is the difference between a mix that works and a mix that merely doesn't kill anything.

What the ready-made bags actually contain

Commercial bonsai soil varies enormously in quality, and the price tells you less than the ingredient list.

Good: a stated blend of akadama, pumice, and lava — sifted, with particle sizes given in millimetres. This is what you want, and it will look like gravel.
Acceptable: pumice-and-lava blends without akadama, sometimes with a small bark fraction. Perfectly serviceable, often better value in North America.
Poor: anything described as "potting mix for bonsai", sold damp, dark, and fine-textured. This is houseplant compost with a bonsai label and a markup.

The single most useful thing on a bag is a stated particle size. If the manufacturer doesn't mention it, they are probably not sifting, and you will be paying for dust.

Three recipes that work

Parts are by volume, and every component should be sifted before use.

Conifers and pines: 1 akadama, 1 pumice, 2 lava. Sharp drainage for Japanese Black Pine, Scots Pine, Shimpaku Juniper and Rocky Mountain Juniper, plus drought-adapted broadleaves like Olive and Rosemary.
Deciduous: 2 akadama, 1 pumice, 1 lava. More retention for Japanese Maple, Trident Maple, Chinese Elm, Hornbeam and Crabapple.
Indoor and tropical: 2 pumice, 1 lava, 1 composted bark. Forgiving of irregular watering for Ficus, Fukien Tea and Sageretia.

Two exceptions are worth knowing. Acid-lovers — Satsuki Azalea, Blueberry, Gardenia — want kanuma rather than akadama. Succulent species such as Dwarf Jade and Desert Rose want a gritty, near-inorganic mix with no bark at all.

How much soil you actually need

Estimating by pot size saves a second trip. As a rough guide, a small pot up to about 15cm takes 0.5-1 litre, a medium 20-25cm pot takes 2-3 litres, and a large 30cm-plus pot takes 5-8 litres. Add roughly 20% for sifting losses — the dust you screen out is soil you paid for but cannot use.

For a first purchase, four litres covers a couple of small trees with enough left over to top-dress. Buying components individually generally means starting with 10-15 litres of each, which is why the DIY route only pays off across several trees.

What it costs, and where the money goes

Akadama is the expensive component and the one that breaks down fastest, which is why many growers outside Japan reduce or drop it in favour of pumice. Pumice and lava are cheap, permanent, and widely available from landscape suppliers in far larger bags than bonsai retailers sell — often the single biggest saving available to you.

Two pieces of kit change the economics. A three-screen sifter pays for itself within a couple of bags by letting you use material you would otherwise discard. And because pumice and lava don't degrade, you can wash and reuse them at the next repot — only the akadama fraction genuinely needs replacing.

Buying checklist

Before you pay, check the bag for these:

Stated particle size, ideally in the 2-6mm range. No size on the label means no sifting.
Named components. "Premium blend" is not an ingredient list.
Dry weight. A heavy, damp bag is holding water it should not be holding.
No peat, no coir as the main component, no fine black compost.
No fertiliser included. You want to control feeding yourself, and pre-fed mixes burn freshly cut roots.

If you are choosing your very first bag and don't want to think about ratios, a sifted pumice-and-lava blend is the most forgiving starting point — it is nearly impossible to overwater a tree in it, which is the mistake beginners actually make.