Kanuma acid soil for bonsai - 5/10 mm grain - 17 lt bag

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 in colour, with a light, porous grain. Here the original bag holds 17 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 through the drainage hole. This dual behaviour is why acid-loving plants thrive in it: the roots find constant moisture without sitting in a closed, airless substrate.

It is a soft material. Within a few seasons the granule tends to soften and compact, especially in climates with repeated frosts, so keep an eye on it at repotting time. For this very reason we recommend mixing kanuma 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
• Original 17 litre bag
• Free-draining, with higher water absorption than akadama
• Suitable for acid-loving plants

Which grain and for which plants

5/10 mm is a coarse grain. It is at home 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. It also works very well as a bottom layer, beneath a finer-grained substrate. The 17 litre bag comfortably covers several medium-sized repottings or the preparation of a generous mix.

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

How to use it at 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 drainage layer on the bottom, then settle 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 thoroughly 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, suggest 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 well, and it is also recognisable at a glance by its pale colour.

Is the 5/10 mm grain suitable 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 drainage layer at the bottom.

What's included

• Japanese kanuma, 5/10 mm grain
• Original 17 litre bag

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