Best Pumice for Bonsai

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Pumice is a light volcanic rock full of tiny pores, and it does the structural work in a bonsai mix. Unlike compost it does not compress or rot, so the air gaps you build at repotting are still there years later. It holds a little water in its pores and gives it back slowly. What varies between bags is particle size, how much fine dust rides along, and whether the material has been washed and screened. We weighed consistency of grade above all, because a bag sold as one size that arrives as three ruins the drainage you planned. Dust load mattered next, since rinsing a sack by hand costs an afternoon. Coarse pumice suits conifers, deeper pots and wet climates. Finer grades suit shallow trays and small trees. Pure pumice suits growers who want a forgiving, hard to kill base to build on.