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

What it is and where it comes from

Kanuma is a Japanese clay soil with a low pH, quarried and graded into granules. It is easy to recognise: pale, almost ivory colour, with a light, porous grain. This pack holds 5 litres with a 5/10 mm grain size.

How it behaves in the pot

The granule absorbs more water than akadama while still letting the surplus run out of the drainage hole. This dual behaviour is why acid-loving plants thrive in it: the roots find steady moisture without sitting in a closed, airless substrate.

It is a soft material. Over a few seasons the grain tends to soften and compress, especially in climates with repeated frosts, so keep an eye on it at repotting time. For this very reason kanuma soil is best mixed with other soils, which give it structure and keep it open for longer.

Features

• Japanese clay soil with an acid reaction (low pH)
• Grain size 5/10 mm
• 5 litre pack
• Free-draining, with water absorption higher than akadama
• Suitable for acid-loving plants

Which grain and for which plants

5/10 mm is a coarse grain. It works well in deeper pots and on medium to large specimens, where volume and air are needed; on shohin and shallow pots it is out of proportion with the root mass. The 5 litre pack is a modest quantity, suited to a few repottings or for use as a bottom layer beneath a finer-grained substrate.

Kanuma soil is the classic choice for satsuki azaleas, camellias, rhododendrons and generally for species that suffer in alkaline substrates. It can be used on its own or alongside materials that stay stable over time, such as pumice or volcanic lapillus.

How to use it when repotting

First of all, sieve it. Even with a 5/10 mm grain there is always some transport dust and, if it ends up in the pot, it clogs the gaps and slows drainage. One pass through the sieve is enough.

Lay a draining layer on the bottom, set the plant in place and fill from the edges towards the centre, working the granules between the roots with a chopstick without pressing: kanuma is friable and a crushed granule does not recover. Once repotting is done, water generously until the water running from the hole is clear.

Frequently asked questions

Can kanuma be used on its own?

It can, and it is common practice with azaleas. We do, however, recommend mixing it with other soils: being a soft material, on its own it tends to compact sooner, whereas adding a harder component keeps the substrate open between one repotting and the next.

How does it differ from akadama?

Akadama is a general-purpose soil, while kanuma has a low pH and is intended for acid-loving plants. In terms of water, kanuma absorbs more than akadama while still draining freely, and it is also recognisable by its pale colour.

Is the 5/10 mm grain right for azaleas in small pots?

Better not. In shallow pots and on small plants this grade leaves gaps that are too wide between the azalea's fine roots. At those sizes a finer grain is preferable, while 5/10 mm comes into its own on large specimens and as a draining layer on the bottom.

What is included

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

Anyone who prefers to measure out the components themselves can build their own blend on the custom soil mix page.