Vermiculite is a naturally occurring mineral (hydrated magnesium aluminium silicate) that expands into accordion-like particles when heated to high temperatures. In horticulture, it is used as a growing medium component that retains moisture and nutrients while providing some aeration. Unlike perlite, vermiculite holds significantly more water and has a moderate cation exchange capacity (CEC), meaning it can temporarily hold and release nutrient ions.
Key Facts
- Retains 3β4 times more water than perlite β better for moisture-loving seedlings and cuttings
- Moderate CEC allows it to buffer and slowly release nutrients
- pH slightly alkaline (7.0β7.5) β can raise pH in acidic mixes
- Not suitable as a standalone hydroponic medium β too water-retentive for most systems
- Best uses: seed starting, propagation mixes, top layer over germinating seeds
- Often blended with perlite in propagation media (50:50) to balance moisture and aeration