Kiryuzuna is a premium Japanese volcanic substrate mined from ancient deposits near Kiryu City in the Akagi Mountains, Gunma Prefecture. Prized by bonsai growers and orchid enthusiasts worldwide for its exceptional drainage and durability.
Rich in iron oxide (Fe₂O₃), Kiryuzuna offers outstanding drainage and aeration while retaining enough moisture within its porous particles for healthy root development. Harder and more angular than Akadama, it resists breaking down over time and has no tendency to compact, meaning less frequent repotting. Substrate typically lasts around 3 years before needing replacement.
Best suited for:
- Orchids, including oriental orchids
- Bonsai, especially pine and juniper (the first choice for conifer repotting)
- Weakened or sick pine bonsai (potting in pure Kiryuzuna is advisable for recovery)
- Ornamental plants and wildflowers
- General potted plants (mixed with other potting soil)
- As bottom stones for drainage in pots and planters
Key properties:
- High water permeability, helping prevent root diseases after repotting
- Excellent air drainage, delivering more oxygen to roots
- No tendency to soil compaction, very structurally stable
- Slightly acidic (pH ~6.5), ideal for acid-loving species
- Rich in iron, calcium, and magnesium
How to use:
Use pure for conifer bonsai, orchids, and recovering trees. Mix with Akadama or other potting soil for general use (decide ratios case by case). A common bonsai mix is 70% Kiryuzuna + 30% Akadama for pines, or 30% Kiryuzuna + 70% Akadama for deciduous trees.