Kanuma is volcanic soil from Japan that is used for growing Bonsai. It is sourced from Kanuma City in Tochigi, which is 100km away from the capital city, Tokyo. Kanuma (also referred to as kanuma-pumice) comes from the eruption of Mount Akagi around 45, 000 years ago. The mineral is mined and dried using 300-degrees Celsius of hot air before it is packaged up.
Kanuma comes in different grain sizes and is characterized by its soft pale yellow color, its lightness, and soft airy structure. Compared to its counterpart, akadama, kanuma is more acidic which makes it suitable for growing acid-loving bonsai such as azalea bonsai. Its pH level is at around 5.5 and is suitable for succulents and acid-loving indoor plants as well. In addition, kanuma soil particles are small enough in size to promote the development of plants’ roots resulting in a better and healthier plant because of proficient supply and absorption of minerals and water. Plants benefit from a greater dose of oxygen because of the lightweight characteristic of Kanuma that also prevents moisture in the soil to remain for a prolonged period of time thereby preventing roots from rotting. It also is unlikely to become compact over time. If you often repot your plants, Kanuma saves you a lot of time as it promotes fibrous root growth which makes the roots manageable enough to get rid of excess soil. It also lends an aesthetic touch when used as a top layer around a plant.