Improve seed germination with this naturally occurring, non-toxic mineral. Vermiculite absorbs water and nutrients, releasing them back into the soil as the seedling roots require it. This heat treated product improves aeration and drainage at the roots ? perfect for mixing into seed compost to encourage healthy root growth. With good insulation properties, it is also ideal for covering seeds during sowing. When rooting cuttings, mix vermiculite with compost to promote root establishment. This inert material is also ideal for storing begonias and dahlia tubers over winter.