Bonsai Soil Selection & Mixing Guide — Akadama, Kanuma & Kiryu

The foundation supporting healthy bonsai growth is the soil. Within the limited space of a bonsai pot, soil must properly supply roots with moisture, nutrients, and oxygen. Proper soil selection and mixing dramatically improves bonsai health. Rather than using commercial potting mix as-is, customize blends by species and conditions. This guide covers bonsai soil fundamentals.

Key Soil Component Characteristics

Representative soils used in bonsai and their characteristics:

Akadama (Red Ball Soil) - Red-brown granular soil from the Kanto loam layer - The most common foundation soil for bonsai - Balances adequate water retention and drainage - Particles break down over time, reducing drainage -- choose hard-fired types - Sizes: Large (for pot bottom drainage), medium (base soil), small (for small bonsai)

Kanuma Soil - Yellowish-white pumice-like soil from around Kanuma City, Tochigi Prefecture - Higher drainage than akadama, slightly acidic - Suited for acid-loving species like Satsuki azalea - Often mixed with akadama - Turns whitish when dry, making watering timing visible

Kiryu Sand - Hard granular sand from around Kiryu City, Gunma Prefecture - Very high drainage with almost no water retention - Suited for drainage-priority species like pines - Particles resist breakdown, maintaining structure long-term - Contains almost no nutrients on its own -- supplement with fertilizer

Fuji Sand - Volcanic sand and gravel from around Mt. Fuji - High drainage similar to Kiryu sand - Iron-containing dark color - Heaviness adds pot stability

Keto Soil - Peat-like wetland soil - High adhesiveness for securing roots in rock-planting bonsai - Extremely poor drainage alone -- always mix with other soils

Species-Specific Blend Ratios

Soil blend guidelines matched to species characteristics:

Conifers (Pine, Juniper, Cypress, etc.) - Akadama 6 : Kiryu sand 3 : Fuji sand 1 - Drainage-priority blend. Pines dislike waterlogged conditions - For larger pots, increase Kiryu sand ratio

Deciduous Broadleaf (Maple, Zelkova, Beech, etc.) - Akadama 7 : Kiryu sand 2 : Kanuma 1 - Slightly moisture-retentive blend. Maples prefer water, so higher akadama ratio - If summer water stress is concerning, increase akadama further

Flower/Fruit Trees (Plum, Cherry, Pyracantha, etc.) - Akadama 6 : Kanuma 2 : Kiryu sand 2 - Balanced blend. Flowering and fruiting require adequate moisture and nutrients - Assumes consistent fertilizing

Satsuki Azalea/Rhododendron - Kanuma 8 : Akadama 2 (or pure Kanuma) - Acid-loving species require Kanuma-dominant mix - Adding akadama provides slight moisture retention boost

Balancing Drainage and Retention

The core of soil mixing is balancing drainage and retention.

Why Drainage Matters - Constantly waterlogged roots suffer rot - Oxygen can't reach roots, inhibiting root respiration - Poor drainage allows harmful waste accumulation

Why Retention Matters - Small bonsai pots lose moisture quickly to evaporation - Summer may require multiple daily waterings - Insufficient retention prevents adequate root hydration

Finding Balance - If you can water frequently, prioritize drainage - With limited watering opportunity (busy schedule), lean toward retention - Pot size: Smaller pots dry faster, so slightly increase retention - Location: Windy spots dry faster; factor retention accordingly - Season: Summer dries quickly; consider this when mixing at repotting time

Sifting and Preparation

Pre-use sifting is essential for quality soil environment.

Sifting Procedure 1. Always sift purchased soil before use 2. Remove oversized particles and fine dust (powder) 3. Use only medium-grade particles appropriate to bonsai size 4. Remaining fines impair drainage -- remove thoroughly

Particle Size Guidelines - Large bonsai (pot diameter 30 cm+): Medium to large particles - Medium bonsai (pot diameter 15--30 cm): Small to medium particles - Small bonsai (pot diameter under 15 cm): Extra-small to small particles - Pot bottom drainage: Large akadama or pumice

Find Bonsai on BreederDirect

BreederDirect features various species of bonsai. When purchasing, we recommend consulting sellers about appropriate soil blends for each specimen. Bonsai health starts with soil. Choose the right soil to bring out your bonsai's full potential.