Perlite is a pH-neutral, sterile, safe-to-handle volcanic mineral. Perlite is prepared for gardening use by super-heating it until it expands to more than ten times its original volume. The expanded perlite is full of tiny air bubbles, and its dimpled surface area helps trap moisture. Mixing perlite into your soil, whether it's in a garden or for container plants, helps aerate the soil, protects against extreme climate fluctuations, protects against over-watering and makes moisture readily available to plants. Perlite is available in multiple grades, all of which work well for gardening applications, but fine grades of perlite are preferred for use in outdoor gardens. Plants that require well-drained soil will usually do very well in mixes that contain perlite.
Loosen the soil in the rows you intend to plant, working it as deep as necessary for the plants you're placing in each row--usually between 6 and 12 inches deep. To work the soil, use a rototiller for large areas and a gardening fork for smaller areas.
Spread a 4-inch layer of fine horticultural perlite over the area to be planted. If you're covering a large area, pour out a pile of perlite every few feet and use a rake to help spread it out into a reasonably even layer.
Work the perlite into the soil with the same tool you used before to work the soil.