Vermiculite is a soil amendment used in many commercial and homemade potting mixes. It is prized in these mixes because it is lightweight, sterile and helps ensure the mixes drain properly and don't become waterlogged. Vermiculite is a form of mica that expands when it is heated to extreme temperatures, which also enables it to retain nutrients and moisture in the soil. If vermiculite isn't available, there are other soil amendments that can be used to replace it.
Mix one part compost and one part peat moss in a large bucket or tub. Use a purchased sterile compost or bake garden compost at 280 degrees F for 30 minutes to sterilize it. Sterilization ensures there are no weed seeds or disease pathogens in the soil.
Add one part perlite to the compost mixture. Perlite is a volcanic material that resembles white pieces of foam and has many of the same properties as vermiculite, though it doesn't retain moisture or nutrients as well. Purchase perlite at garden supply stores.
Add one part coarse builder's sand or one part calcined clay, which looks like cat litter, if perlite is not available. These materials add the soil aeration and drainage properties of vermiculite, but do not provide moisture or nutrient retention.
Check the soil moisture in the potting mix one to two times a day when replacing vermiculite with perlite, sand or calcined clay, as these mediums dry out more quickly. Water when the soil surface begins to feel dry or when recommended for the types of plants you are growing.
Fertilize plants weekly with a half-strength liquid fertilizer, since materials other than vermiculite do not retain nutrients well. Fertilize vermiculite mixes every two to four weeks.