Best Lava Rock for Bonsai Soil

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Lava rock is the sharp, angular component in a classic bonsai mix. Its jagged faces lock together so the soil column stays open, and its rough surface gives fine roots something to grip and ramify against. Like pumice it does not decompose, which is the whole point of an inorganic soil. What varies is particle size, angularity, how much dust comes in the bag, and whether the rock is red or black scoria. We weighed how well each product held its grade after handling, since brittle lava crumbles into fines before it reaches the pot. Sharpness mattered too, because rounded material packs tighter. Coarser grades suit pines, junipers and larger pots. Finer grades suit deciduous trees and shallow containers. Growers in wet climates lean harder on lava, while those in hot, dry places usually pair it with more akadama.