For Japanese maples, many “problems” come from the same place: the roots. A good substrate isn’t a “rich” substrate—it’s a living, airy, free-draining root environment that stays fresh without ever turning into a compact sponge.

The goal is simple: the right ratio of air + water, all year round.

Understanding what a Japanese maple expects from the soil

A Japanese maple dislikes both:

soil that dries out completely,
and soil that stays cold and saturated (suffocation, weak roots).

The right root environment is:

moist but not waterlogged,
free-draining, with a stable structure,
able to stay fresh in summer and breathable in winter.

To avoid: commercial “ericaceous soil”

It’s a classic. You often hear “Japanese maple = ericaceous soil”. In practice, bagged ericaceous soil is very often too fine (often peat-based), and it can:

compact over time,
hold too much water in cold periods,
become hydrophobic when it dries (water runs off instead of soaking in).

In short: it’s not a great long-term substrate, especially in containers.

What a Japanese maple wants isn’t “acidity”—it’s structure first.

In a container: the reliable recipe

The pot is part of the drainage

Large, unobstructed drainage holes.
If possible, slightly raise the pot (so water can drain freely).
Avoid permanent standing water in a saucer.

The substrate: organic + mineral

The best guideline is a structured mix, not a “fine” one.

Recommended base:

60–70% a quality structured horticultural substrate (fibres, composted bark, etc.)
30–40% a draining mineral fraction (pumice, lava rock/pozzolan, horticultural grit)

This mix:

keeps moisture without becoming soggy,
stays airy,
compacts less,
and is more forgiving in both summer and winter.

How do you know your substrate is too fine?

Typical signs:

water takes a long time to drain,
the surface “crusts”,
the pot stays heavy for a long time,
watering becomes difficult (either it runs off, or it stays spongy),
few fine roots when you check the rootball.

In the ground: you don’t “replace” the soil—you improve it

Free-draining / light soil

Keep it simple:

plant at ground level,
lightly improve with well-matured organic matter (not large amounts of pure potting soil),
mulch.

Clay / compact soil

The classic mistake is adding a lot of fine potting soil or ericaceous soil: it creates a basin that holds water.

A more reliable approach:

work on soil structure (aerate, decompact),
incorporate materials that help maintain air (depending on your soil),
if needed, plant on a slight mound rather than in a “bowl”.

A good rule of thumb: after rain, water should not sit around the base of the tree.

Costly mistakes (that we see all the time)

A 100% “fine potting soil” mix in a pot → compaction + suffocation.
Pure ericaceous soil → unstable (too fine, too water-retentive, sometimes hydrophobic).
A saucer that stays full → roots under constant stress.
In the ground, a “hole filled with good potting soil” in heavy soil → bathtub effect.
Mulch piled against the trunk → constant moisture at the collar.

Need a very practical opinion?

Tell us:

container or in the ground,
pot size,
your current substrate composition,
soil type if planting in the ground,
and we’ll tell you whether your mix is too fine, too free-draining, or just right.

FAQ

What is the best substrate for a potted Japanese maple?

A structured mix: a quality horticultural base + a draining mineral fraction (pumice/pozzolan). The goal is a substrate that stays fresh but airy.

Can I plant a Japanese maple in ericaceous soil?

We don’t recommend using bagged ericaceous soil on its own: it’s often too fine, compacts, and holds too much water. Aim for structure (air + drainage).

Why does my substrate become hydrophobic?

Very peaty or overly fine mixes can dry out internally and then repel water. Improve structure (mineral fraction, fibres) and water thoroughly rather than with small frequent top-ups.

My soil is clay—what should I do?

Avoid the “bathtub” effect. Work on soil structure, improve drainage, and if necessary plant on a slight mound.

Pumice or lava rock (pozzolan): which should I choose?

Both work well. The key is adding a stable mineral fraction to maintain air and improve drainage.

Substrate and drainage for Japanese maples