Vermiculite
/vɚˈmɪkjəˌlaɪt/
Definition
Vermiculite is a lightweight mineral material used in potting mixes and seed-starting media. It is made by heating a layered mica mineral until it expands into soft, absorbent particles. In horticulture, vermiculite stands out for holding both water and some nutrients while still adding air space around roots. It is sterile, pH near neutral, and often blended with other ingredients rather than used alone.
Use in Gardening
- Seed-starting support: vermiculite helps keep young roots evenly moist, which can improve germination and reduce drying between waterings. It is often used in seed-starting mixes or as a light surface covering over sown seeds.
- Moisture balance in potting mixes: When blended into container media, vermiculite increases water retention and helps hold some dissolved nutrients near the roots. This can be useful for plants that prefer steady moisture rather than fast drying.
- Propagation and storage: vermiculite is used around cuttings, bulbs, corms, and tubers because it cushions plant parts and limits rapid moisture loss. In some storage uses, it helps reduce shriveling without keeping tissues overly wet.
- Best fit and limits: It is usually less suitable for plants that need sharp drainage, such as many succulents and cacti. In those cases, a coarser material with more air space is often a better choice.