Vermiculite Vermiculite added to the garden or vermiculite in potting soil increases water and nutrient retention and aerates the soil, resulting in healthier, more robust plants. Perlite may also be found in potting soils, but vermiculite is far superior for water retention. Vermiculite, although less aerating than perlite, is the amendment of choice for water-loving plants. What is Vermiculite Vermiculite is a naturally occurring non-toxic Magnesium Alumino Silicate mineral, when heated at a controlled rate, it expands to give a sterile structure, capable of absorbing large amounts of water. Read more about vermiculite at Gardening Know How. Benefits Ideal for seed germination, pricking out and houseplant compost. Absorbs and holds nutrients. Ensures moisture is held near the roots. An excellent insulator, it reduces the fluctuations of temperature when used as a seed covering.