A naturally occurring mineral expanded by heat into lightweight, accordion-shaped particles. Excellent water retention and aeration. Used in seed-raising mixes and for starting cuttings. Provides some slow-release potassium and magnesium.
Vermiculite is produced by mining mica minerals and heating them to high temperatures, causing them to expand into accordion-like flakes. This creates an excellent growing medium component that holds moisture and nutrients while remaining lightweight. In Australia's variable climate, vermiculite is particularly useful for gardeners in arid and semi-arid zones (zones 9-10) where water retention is crucial.
When mixing potting soil, combine vermiculite with peat moss or coco coir and perlite to create a well-draining yet moisture-retentive medium. It's especially valuable for seed raising during spring (September-November) and autumn (March-May) when consistent moisture is essential for germination. Vermiculite can be purchased at Bunnings and most garden centres across Australia in various grades - fine for seedlings, medium for general potting.
Vermiculite works well for propagating cuttings, raising vegetables from seed, and improving native plant mixes in sandy soils. However, it's less suitable for succulents and drought-tolerant plants that prefer faster drainage. In humid tropical zones (1-3), use sparingly to avoid waterlogging. Always ensure good drainage by combining with perlite or coarse sand, especially during wet winter months in temperate regions. Store unused vermiculite in a dry location to maintain its moisture-absorbing properties.