Pumice

Volcanic Rock for Added Drainage

When it cools, the gases are trapped inside the hardened rock, making it light enough to float. In the ocean, rafts of pumice have been seen floating in the currents, sometimes with plants growing on them!

Huge beds of pumice exist near long extinct volcanoes and are mined for use as cosmetic tools (pumice stones) and in horticulture as a soil additive.

Pumice has the quality of adding drainage to high water capacity materials such as peat or coir fiber, due to the tiny air pockets trapped inside it.

It is added to many soilless mixes for growing many kinds of plants, including cacti and succulents. Even adding a small percentage of pumice to the mix can make all the difference to add the fast drainage that succulent plants require.

I’ve used pumice on its own to propagate some very finicky plants such as Daphne cneorum, and added it in large amounts as much as a third by volume to soil mixes for some conifers and ericaceous plants which are notoriously hard to root due to root rot in high water retaining mixes.

Available in many colours depending on the chemical composition of the volcanic rock that forms the pumice; in most cases it ranges from dark charcoal grey to a whitewash colour.

Visit the page on lava rock for information on another volcanic rock.

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