Pour potting soil through a sifter to remove large pieces of mulch, peat moss or other organic materials besides dirt. Organic tree materials soak up moisture and prevent adequate drainage.
Mix in a bucket one-part sifted soil, two-parts pumice, and one-part coir. Pumice is a light weight volcanic material that holds moisture. Pumice conserves enough moisture to prevent your cactus plant from completely drying out. Coir is a fibrous material made from shredded coconuts, which helps retain adequate moisture and air.
Check the bottom of the cactus plant's container to ensure that there are drainage holes at least 1/2 inch in diameter. Pour the soil mixture into the container up to 1 inch from the top.
Wrap a piece of newspaper around the cactus to keep you from getting poked. Place the cactus inside of a hole made in the dirt that is twice the size of the root ball. Pack soil around the base.
Spread a 1-inch layer of gravel over the top of the soil. By spreading gravel, gardeners reduce the risk of the cactus contracting a disease from splashing water.