Vermiculite 4 -8 mm 100L Vermiculite is treated in a number of ways, including heating to nearly 2,000 degrees Fahrenheit. It can retain air, water and nutrients very well. This makes it ideal for hydroponic growing. It has a good pH buffering ability. Vermiculite is also used in the construction industry as an insulator. Vermiculite for Horticulture in Hydroponics (hydroponics cultivation)