Kanuma acid soil for bonsai - 2/5 mm grain - 10 litre pack

What it is and where it comes from

Kanuma is a Japanese clay soil of pumice origin, quarried in the area it takes its name from. It comes as pale, light granules with a low pH that make it the benchmark substrate for acid-loving plants. Here it is graded at 2/5 mm and packed in a 10 litre tub.

How it behaves in the pot

The granule is porous and absorbs more water than akadama, while still letting the excess drain away without clogging the root ball. This twofold behaviour is why azaleas do so well in it: they stay moist between waterings without the fine roots suffocating.

The structure stays open and well aerated. It must be said, though, that kanuma is soft: over time, especially after repeated frosts, the granule tends to break down and compact, which is why many growers prefer not to use it pure and pair it with a more stable material. When wet it turns darker, which makes it easy to read the moisture level of the substrate at a glance.

Features

• Japanese clay soil for bonsai
• Grain size 2/5 mm
• 10 litre pack
• Low pH, suited to acid-loving plants
• High water absorption, greater than akadama
• Good drainage

Which grain and for which plants

The 2/5 mm is the most versatile size in the range: it covers shohin and small pots, but also works well on medium-sized specimens, filling the gaps between roots without leaving voids. It is used in the body of the substrate and, if a uniform surface is needed, as a top dressing too.

Satsuki azaleas first and foremost, then camellias, rhododendrons, kalmias and heathers: anything that suffers in alkaline substrates. Anyone looking for a general purpose bonsai soil would do better with akadama; kanuma is a specific material, and on a conifer or an elm it makes no sense.

How to use it when repotting

Sieve it first. The dust created in transport must be removed, otherwise it settles at the bottom and blocks drainage. A layer of the coarser grain recovered from sieving goes on the bottom of the pot, then you carry on with the rest.

Work it between the roots with a chopstick, without tamping: the granule is soft and crumbles under pressure. After repotting, water thoroughly, several times, until the water runs clear from the drainage holes. That first generous watering also helps settle the material around the nebari.

Frequently asked questions

Can kanuma be used pure?

We recommend mixing it with other soils. On its own it holds a great deal of water and, being a soft granule, it tends to break down over the years: lightening it with a more stable, free-draining material extends the life of the substrate between repottings.

What is the difference compared with akadama?

Kanuma has a low pH and absorbs more water than akadama. Akadama is a good all-round substrate for most species; kanuma is specific to acid-loving plants, where the acidity of the material is part of the result and not a minor detail.

Is the 2/5 mm grain right for my pots?

Yes, if you work with shohin, shallow pots and small to medium plants. On large specimens in deep pots, many prefer a coarser grain for the body of the substrate and keep the 2/5 mm for the surface.

What is included

• Japanese kanuma, grain size 2/5 mm
• 10 litre pack

If you prefer to measure out the components yourself, you can build your own mix on the made-to-measure soil page.