Perlite is a volcanic rock that is exploded like popcorn. The resulting granules are used as a soil additive, or even in place of soil. Particles of perlite also serve to aerate the soil. It has a neutral pH, so it doesn't affect the soil's pH level. It won't deteriorate and will continue to improve your soil's structure for many years. Perlite has the unique ability to increase both the aeration of your garden soil and its water retentive ability.
To start seeds using perlite, use a mixture of 1 part perlite and 1 part moistened peat moss. Fill the pots or seed starting flats and then top off with an eighth inch of the mixture sifted through a fine mesh screen. Use another eighth inch of sifted mixture to cover the seeds. To start seeds directly in the garden, work a 1-inch layer of the mixture into the top 6 inches of the seedbed. Smooth over the surface and plant seeds as usual.
To propagate cuttings using a perlite rooting mixture, combine 2 to 3 parts perlite and one part damp peat moss. Insert cuttings into the mixture and follow your usual propagation procedures. Perlite can also be used to propagate with a cutting misting system.
Transplant potted houseplants into a perlite mix to reduce the weight of their pots. First, add a 2- to 4-inch layer of perlite in the bottom of the pot. Insert the root ball of the transplant and fill in the gap between the root ball and the larger pot with a mixture of half-damp perlite and half-damp peat moss. Additional mixture can also be added to the surface of the soil in the pot.
Use 3 cubic yards for each 1,000 square feet of garden bed to improve the soil in your flower or vegetable garden. Spread the perlite on the surface of the soil and incorporate it by rototilling or by turning over the soil with a garden spade. Repeat rototilling or digging in order to more fully incorporate the perlite into the soil.