Bonsai Soil Selection and Blending Guide | Akadama, Kanuma Soil, and Kiryu Sand

The foundation supporting healthy bonsai growth is "soil." In a limited pot space, selecting and blending the right soil is crucial to properly supply the roots with moisture, nutrients, and oxygen. Rather than using commercial potting soil as-is, tailoring the blend to suit the tree species and environment can dramatically improve bonsai growth. This article covers the fundamentals of bonsai soil.

Characteristics of Major Bonsai Soils

Here are the representative bonsai soils and their characteristics.

Akadama Soil (Red Ball Soil) - A reddish-brown granular soil extracted from the Kanto loam layer - The most common foundational soil for bonsai - Offers both appropriate water retention and drainage - Choose hard-grained varieties, as soft particles reduce drainage - Grain sizes: Large (for pot drainage), Medium (primary soil), Small (for miniature bonsai)

Kanuma Soil - A yellowish-white volcanic pumice soil mined near Kanuma City, Tochigi Prefecture - Higher drainage than akadama soil with a slightly acidic nature - Ideal for tree species that prefer acidic conditions, such as Satsuki and Azalea - Often mixed with akadama soil - Turns whitish when dry, making watering timing easy to recognize

Kiryu Sand - A light-colored sand and gravel mined near Kiryu City, Gunma Prefecture - Extremely high drainage with minimal water retention - Suitable for tree species prioritizing drainage, such as pines and cypresses - Hard grains resist breakdown, maintaining shape over long periods - Contains almost no nutrients on its own, so fertilization is necessary

Fuji Sand - Volcanic sand and gravel from areas around Mt. Fuji - High drainage similar to Kiryu sand - Contains iron, giving it a darker appearance - Heavy weight helps stabilize pots

Keto Soil - A peaty soil from wetland areas - Highly adhesive; used to secure roots in rock-attached bonsai - When used alone, drainage becomes extremely poor, so mix with other soils

Recommended Blending Ratios by Tree Type

Here are guidelines for soil blends tailored to different tree species.

Conifers (Pines, Juniper, Cypress, etc.) - Akadama 6 : Kiryu Sand 3 : Fuji Sand 1 - A blend prioritizing drainage. Pines dislike excessive moisture, so well-draining soil is essential - For larger pots, you can increase the Kiryu sand ratio further

Deciduous Broadleaf Trees (Maple, Zelkova, Beech, etc.) - Akadama 7 : Kiryu Sand 2 : Kanuma Soil 1 - A blend slightly favoring water retention. Maples prefer moisture, so increase akadama ratio - If concerned about summer drying, increase the akadama ratio further

Flowering and Fruiting Species (Plum, Cherry, Firethorn, etc.) - Akadama 6 : Kanuma Soil 2 : Kiryu Sand 2 - A well-balanced blend. Adequate water retention and nutrients are needed for flowers and fruit - This blend assumes consistent fertilization

Satsuki and Azalea - Kanuma Soil 8 : Akadama 1 (or Kanuma soil alone) - Since these species prefer acidic conditions, Kanuma soil is the primary component - Adding akadama slightly increases water retention

Balancing Drainage and Water Retention

The core of soil blending is balancing drainage and water retention.

Why Drainage is Important - Roots constantly submerged in water develop root rot - Oxygen can't reach roots, blocking respiration - Poor drainage allows harmful waste to accumulate in the soil

Why Water Retention is Important - Small bonsai pots dry out quickly - Especially in summer, watering may be needed multiple times daily - Insufficient water retention prevents roots from absorbing enough moisture

How to Balance - Generally, prioritize drainage if you can water frequently - If you're away often and watering is limited, increase water retention slightly - Pot size: Smaller pots dry faster, so slightly increase water retention - Location: Well-ventilated spots dry quickly, so adjust retention accordingly - Season: Adjust the blend slightly when repotting to account for summer drying

Sifting and Preparing Soil

Sifting soil before use is essential for creating a high-quality soil environment.

Sifting Steps 1. After purchasing soil, sieve it before use 2. Remove overly large particles and fine dust (powder) 3. Use only medium-grain particles appropriate for your bonsai size 4. Remove dust thoroughly, as it reduces drainage

Grain Size Guidelines - Large bonsai (pot diameter 30cm or more): Medium to large grains - Medium bonsai (pot diameter 15–30cm): Small to medium grains - Miniature bonsai (pot diameter 15cm or less): Extra-small to small grains - Pot drainage layer: Large akadama or pumice stones

Annual Bonsai Care Schedule

Bonsai care changes with the seasons. Understanding the yearly management flow helps you perform the right tasks at the right time.

Spring (March–May) The most critical season when new growth emerges. Many tasks concentrate here: repotting, bud pinching, and resuming fertilization. Perform bud pinching and trimming as new shoots develop, balancing the tree shape. Repotting is best timed just before new growth emerges.

Summer (June–August) The season when watering is most critical. Watering twice daily (morning and evening) may be necessary. Provide shade if leaves scorch, and place in a well-ventilated spot. Avoid repotting or heavy pruning in midsummer; focus on maintaining the tree's vigor.

Autumn (September–November) A beautiful viewing season with fall colors, also a preparation period for next spring. Apply wire and light pruning, beginning winter preparations. After leaves drop, assess branch placement and plan pruning of unnecessary branches.

Winter (December–February) Deciduous trees enter dormancy. Water sparingly but never let soil completely dry. Provide frost protection for cold-sensitive species. Evergreens remain slowly active in winter, so don't neglect watering.

Common Beginner Mistakes and Solutions

Mistake 1: Over- or Under-Watering Overwatering causes root rot; underwatering causes death. The basic rule is to water thoroughly when the pot surface turns white and dry.

Mistake 2: Pruning at the Wrong Time Heavy pruning outside the growing season weakens the tree. Always check the right timing for your tree species before working.

Mistake 3: Insufficient Light Most bonsai require outdoor management. Keeping them indoors causes weak growth from insufficient light and may eventually kill them.

Find Your Bonsai on Botachoku

Botachoku features a variety of bonsai available for purchase. When buying, we recommend consulting with the seller about the appropriate soil blend for that specific bonsai. Bonsai health begins with soil. With proper soil selection, you can bring out the full charm of your bonsai.