A good soil mix is essential if you expect good growth and health for your Cactus. They prefer a porous alkaline soil. Contrary to popular belief, Cacti don't grow well in plain sand. There are several good brands of commercially available Cactus soils that come prepackaged. For those of you who want to do it yourself, here are a few recommended soil formulas.
Ingredients are available at most garden centers, or larger department stores.
Equal parts commercial potting soil and builders sand. Also add one Tablespoon each of ground bone meal and ground limestone per gallon of mix. Two parts soil mix, one part fine to small size pumice, one part leaf mold. If you are making your own soil it would be a good idea to sterilize the mixture by baking in an oven at 400 degrees F for 60 minutes. This kills most bacteria, larvae, weed seeds and insect eggs.