Kanuma  Japanese Pumice 14L (3-5MM GRADE) 

A granular Japanese potting medium for Ericaceous (Acid Loving) Bonsai. Its acidic, soft, highly water and nutrient retentive soil used primarily with Satsuki azaleas. Can be easily crushed so be careful when working with Kanuma soil around the root ball. This particular Bonsai potting mix comes from the Kanuma Area of Japan which is basically the center of Azalea Bonsai Growing. Again, you must understand as with Akadama, that Kanuma soil is the stuff that the Japanese have out in their back yards it's their "dirt." This material is dug out from 10 feet down, allowed to dry, crushed, and then sorted as to grain sizes. This Bonsai growing medium is more acidic than Akadama, and therefore, used mainly for Azaleas, Camellias, Gardenias and other acid-loving Bonsa.

Kanuma: A Specialized Growing Medium for Bonsai and Plants

What is Kanuma?

Kanuma is a type of volcanic pumice-like material, primarily used in bonsai cultivation. It's a lightweight, acidic substrate with excellent drainage properties, making it ideal for bonsai trees and other acid-loving plants. It’s mined in Japan and is known for its porous texture, which helps regulate moisture levels while providing essential aeration to the roots.

Uses of Kanuma in Bonsai

1. Ideal for Bonsai Trees

• Drainage and Aeration: Kanuma's porous structure allows for excellent drainage and air circulation, which is crucial for bonsai roots that need to avoid waterlogging.
• Root Development: The medium encourages healthy root growth and prevents compaction, giving bonsai trees room to grow.
• Acidic Environment: Many bonsai species, particularly conifers (like pines and junipers), thrive in slightly acidic soils. Kanuma has a naturally acidic pH (around 5.5–6.0), which supports the growth of these plants.

2. Best for Specific Bonsai Species

• Kanuma is best suited for acid-loving bonsai trees such as:
  • Pines (e.g., Japanese Black Pine, Scots Pine)
  • Junipers
  • Azaleas
  • Ficus
  • Certain types of maples (e.g., Japanese Maple)
• It is particularly beneficial for trees that are sensitive to high alkalinity in the soil.

Uses of Kanuma for Other Plants

1. Acid-Loving Plants

• Azaleas and Rhododendrons: Like bonsai, these plants prefer acidic soils, and Kanuma provides a great environment.
• Carnivorous Plants: Plants like Venus flytraps, Sarracenia, and sundews prefer acidic, well-draining soil. Kanuma provides the perfect medium.
• Camellias and Gardenias: These plants thrive in slightly acidic soil, and Kanuma helps maintain the ideal pH.

2. Orchids

• Some orchids, especially those grown in pots, can benefit from Kanuma as it improves drainage and aeration while maintaining moisture in the roots.

3. Indoor Plants

• Plants like peace lilies or ferns that prefer slightly acidic conditions can also benefit from the use of Kanuma in their potting mixes.

How to Use Kanuma in Gardening

1. As a Pure Medium

• For Bonsai: Kanuma can be used alone as a potting medium for bonsai. This allows for maximum control over moisture and root health, especially for trees that need consistent yet non-waterlogged soil.
• For Other Plants: For plants that require acidic conditions, you can use Kanuma by itself, especially in pots where drainage and pH control are key factors.

2. Mixed with Other Components

• For Bonsai: Kanuma is often mixed with other soil components such as akadama (a clay-based substrate), pumice, or lava rock. A typical mix might be:
  • 50% Kanuma
  • 30% Akadama
  • 20% Pumice or Lava Rock
  • This blend provides a balanced mix of aeration, drainage, and moisture retention.
• For Other Plants: When mixed with other components like perlite or bark, Kanuma helps balance moisture retention and drainage, creating an optimal growing environment for a variety of plants.

Advantages of Using Kanuma

1. Excellent Drainage: Prevents root rot by ensuring proper water flow.
2. Promotes Root Health: Its structure encourages strong root systems in bonsai and other plants.
3. pH Control: Perfect for acid-loving plants, maintaining a slightly acidic pH.
4. Long-Lasting: Kanuma does not break down quickly, so it lasts longer than organic mediums like peat or compost.
5. Improved Aeration: Helps maintain healthy oxygen levels for the roots.

How to Care for Plants in Kanuma

• Watering: While Kanuma holds moisture well, it’s important not to overwater. Bonsai trees especially need to be watered only when the soil begins to dry out.
• Fertilizing: Kanuma itself doesn’t provide nutrients, so regular feeding with appropriate fertilizers is essential. For bonsai, a slow-release or liquid fertilizer is commonly used.
• Repotting: Kanuma doesn't degrade as quickly as organic materials, so repotting every couple of years (rather than annually) is usually sufficient.

Precautions When Using Kanuma

• pH Sensitivity: Kanuma’s acidic nature means it’s unsuitable for plants that prefer neutral to alkaline conditions, such as many vegetables and herbs.
• Weight: Kanuma is relatively light, but when mixed with other heavy materials, it can add up. Ensure your pots are suitable for the combined weight.

Kanuma vs. Other Soils