Pile Of White Pumice Rock
(Image credit: MonaMakela)

The perfect potting soil varies depending on its use. Each type of potting soil is specifically formulated with different ingredients whether the need is for better-aerated soil or water retention. Pumice is one such ingredient used as a soil amendment. What is pumice and what does using pumice in soil do for plants? Read on to find out about growing plants in pumice.

What is Pumice?

Pumice is fascinating stuff, borne out of the superheated earth. It is basically whipped volcanic glass that is made up of tiny air bubbles. This means that pumice is a lightweight volcanic rock that makes it perfect for use as a soil amendment.

The airy rock is ideal for use with cacti and succulents as well as other plants that require excellent drainage and air circulation. Plus, the porosity of pumice allows microbial life to thrive while maintaining soil structure better than perlite. Planting with pumice also has the advantage of a neutral pH along with a variety of trace materials.

There are many advantages to growing plants in pumice. It reduces water runoff and fertilization by increasing soil absorption in sandy soils. It also absorbs excess moisture so roots don’t rot. Additionally, pumice improves aeration and stimulates the growth of mycorrhizae.

Pumice doesn’t decompose or compact over time like other soil amendments, which means it helps to maintain soil structure. It also keeps clay soils loose over time for continued soil health. Pumice is a natural, unprocessed organic product that doesn’t decompose or blow away.

Using Pumice as a Soil Amendment

To improve drainage for plants such as succulents, mix 25% pumice with 25% garden soil, 25% compost, and 25% large grain sand. For plants that are prone to rotting, like some euphorbias, amend the soil with 50% pumice, or in lieu of amending the soil, fill the planting hole with pumice so the roots are surrounded by it.

Pumice can be used as a topdressing to absorb rainwater that puddles around plants. Create a moat around the plant with vertical tunnels. The moat should be at least a foot (30 cm.) away from the base of the plant. Funnel pumice into the vertical holes.

For potted succulents, combine equal portions of pumice to potting soil. For cacti and euphorbia, combine 60% pumice with 40% potting soil. Start cuttings that rot easily in pure pumice.

Pumice can be used in other ways as well. A layer of pumice will absorb spilled oil, grease, and other toxic liquids. Once the fluid has been absorbed, sweep it up and dispose of it in an eco-friendly manner.

Amy Grant

Amy Grant has been gardening for 30 years and writing for 15. A professional chef and caterer, Amy's area of expertise is culinary gardening.