Bonsai Soil: What to Buy and What to Mix
Our stance
Buy the components and mix them yourself. Most bagged "bonsai soil" is potting mix with grit sprinkled on top.
Short answer
Buy akadama, pumice, and lava rock separately and mix them yourself — a 1:1:1 blend suits most trees, and about $50 of components fills several small pots. Check the label before you buy anything pre-bagged: if peat or compost is listed first, it's potting soil with grit in it, and it will hold water your roots can't use.
Two different pages could be written about bonsai soil. The one about why — how particle size controls the air-to-water balance, why a shallow pot behaves nothing like a garden bed — is our soil guide. This one is about what to put in the cart.
The short version: bonsai substrate is granular, sifted, and free of dust. Every particle stays a particle when wet. That's the whole specification, and it's why the material list below is short and the brand list is shorter.
Mix your own and you'll pay roughly half what pre-bagged blends cost, and you'll know what's in it. Use the calculator further down to turn your pot size into dry quarts of each component so you buy once instead of twice.
Our picks at a glance
| # | Pick | What for | Typical price |
|---|---|---|---|
| 1 | Akadama, hard-fired, 1/8–1/4 inch | Base component | $25–45 |
| 2 | Pumice, sifted, 1/8–1/4 inch | Base component | $15–30 |
| 3 | Lava rock (scoria), 1/8–1/4 inch | Base component | $15–30 |
| 4 | Turface MVP | Akadama substitute | $15–25 |
| 5 | NAPA floor-dry #8822 | Budget substitute | $10–25 |
| 6 | A three-screen sieve set | Equipment | $20–40 |
Some links here are, or will become, affiliate links. If you buy through one we earn a commission. It doesn't change your price, and it doesn't change our picks — we'd still tell you to skip the seed kits.
Base component
Akadama, hard-fired, 1/8–1/4 inch
$25–45typical
- What it is
- Fired Japanese clay granules, mined in the Kanto region. Holds water and nutrients while keeping air gaps between particles.
- Why we picked it
- It's the reference material every other substrate is measured against, and it has one feature substitutes don't: it breaks down over two to three years, so when the granules turn soft the soil is telling you it's repotting time.
- Who it's wrong for
- A cold climate where pots freeze hard. Repeated freeze-thaw accelerates the breakdown, and cheaper substitutes hold their structure better in zone 5 and colder.
Base component
Pumice, sifted, 1/8–1/4 inch
$15–30typical
- What it is
- Light volcanic glass, full of tiny pores. Holds moderate water, never compacts, and doesn't break down.
- Why we picked it
- The most forgiving of the three, and the one to lean on if you tend to overwater. Plenty of healthy trees grow in straight pumice — the recipe matters less than the particle.
- Who it's wrong for
- A windy balcony with a very light tree. Pumice is buoyant enough that top-dressed pots can float their surface layer during heavy watering.
Base component
Lava rock (scoria), 1/8–1/4 inch
$15–30typical
- What it is
- Crushed volcanic rock, angular and hard. Holds the least water of the three and adds weight and structure.
- Why we picked it
- It's the anchor in the mix. The angular shape locks particles together so the root ball holds its shape during repotting, and the weight keeps a tall tree from tipping in a shallow pot.
- Who it's wrong for
- A hot, dry climate where you can't water daily — a lava-heavy mix dries fastest of all.
Akadama substitute
Turface MVP
$15–25typical
- What it is
- Calcined clay sold for sports fields. Similar particle behaviour to akadama, at roughly a quarter of the price.
- Why we picked it
- The standard budget swap, and the right call for a first bench. It holds slightly less water than akadama and never breaks down — you lose akadama's built-in repot signal, and you save enough to buy another tree.
- Who it's wrong for
- A show tree, where the reddish akadama surface is part of the presentation, and for growers who use soil breakdown as their repotting cue.
Budget substitute
NAPA floor-dry #8822
$10–25typical
- What it is
- Diatomaceous earth granules sold as an absorbent at auto parts stores. Not clay — a different material with different behaviour.
- Why we picked it
- The cheapest workable substrate in North America, and widely used. Because it holds more water than akadama, cut its share by about a third against the akadama figure and make up the difference with pumice.
- Who it's wrong for
- Anyone who won't sift it. The bag carries fines that will pack down and defeat the point, and the particle size runs inconsistent.
Equipment
A three-screen sieve set
$20–40typical
- What it is
- Stacking screens, usually around 1/4, 1/8, and 1/16 inch, for separating usable particles from dust and oversize.
- Why we picked it
- Sifting is the step that turns cheap material into good substrate. Dust is what clogs the air gaps you paid for, and every bag has some. Buy this once and it outlives the trees.
- Who it's wrong for
- Anyone buying a single small bag of pre-sifted premium substrate — at that scale a kitchen colander gets you most of the way.
What to avoid
Bagged "bonsai soil" that lists peat or compost first
Ingredients are listed by volume. If peat leads, you've bought potting mix with decorative grit, and it will hold water in a two-inch pot for days. This is the most common thing beginner trees are killed by.
Garden potting soil, in any proportion
It's engineered to hold water in a deep container that drains freely. A shallow bonsai pot has no depth for excess water to fall away, so the mix stays saturated and the fine roots rot.
A gravel "drainage layer" in the bottom of the pot
It does the opposite of what it sounds like. Water doesn't cross from fine material into coarse until the fine layer is saturated, so a gravel layer raises the wet zone rather than draining it. Use one consistent mix top to bottom, with mesh over the holes.
Builder's sand
The grains are too fine and too round. They fill the gaps between larger particles instead of holding them open, which is how you get a pot that sets like concrete after two months.
Anything you haven't sifted
Dust and fines migrate to the bottom of the pot and seal it. Five minutes with a screen is the difference between a mix that drains for three years and one that stops draining by midsummer.
How we choose
Soil is the one gear category where the horticulture settles most of the argument, so this page leans on it. Particle size, water retention, and structural durability are measurable properties of a material, and they don't change between brands of the same substrate.
We haven't run side-by-side growth trials, and we won't imply we have. The component picks are the materials with long, consistent track records among growers, plus the two budget substitutes that show up repeatedly in North American club recommendations. Where a substitute behaves differently from what it replaces — NAPA 8822 holding more water than akadama, for instance — we say how to adjust rather than pretending they swap one-for-one.
The ratios in the calculator come from the same species care data as the rest of the site: a tree whose care sheet says "moisture-retentive" gets a different blend from one that says "fast-draining", and the calculator shows its working.
How much of each to buy
Pick your species and measure the pot — this returns the mix ratio and the dry quarts of each component to put in the cart.
setting up the bench…
Species on this page
