What Is Perlite: A Lightweight, Airy Growing Medium Commonly Used in Horticulture

Perlite is a glassy rock formed when acidic lava ejected by volcanoes cools rapidly, and it usually appears grayish-white or light gray. After the ore is crushed and roasted at high temperature, the water inside vaporizes and it expands many times over, turning into very light white granules full of pores. The perlite used in horticulture is this expanded form.

Its standout features are that it is light, airy and well draining. There are large numbers of pores both inside the granules and between them, so mixing it into soil keeps the growing medium loose for a long time and resistant to compaction. Perlite is stable in nature, does not readily rot or decompose, has a pH close to neutral, and contains almost no nutrients itself, so it is usually used together with peat, leaf mold, vermiculite and the like.

In home flower growing, perlite is often blended into potting soil in a certain ratio to grow succulents, orchids and other plants that hate waterlogging, helping excess water drain away quickly. It can also be used on its own or mixed with sand as a medium for cuttings and sowing; its good aeration helps stems root and seeds sprout. In soilless cultivation, it is also often combined with other media to anchor roots and regulate water and air.

When using it, note that dry perlite easily raises dust, so you can spray it damp before mixing soil. Because its ability to hold water and nutrients is relatively weak, the mixing ratio should not be too high, and water and fertilizer management must keep pace accordingly; the granules gradually break down under long-term pressure, so they can be refreshed when you repot or change the soil.