Combine your purchased potting mix with perlite and sand if you are growing Christmas cactus, orchid cactus or other epiphytes. Measure three parts purchased mix, one part sand and one part perlite and combine them in a bucket or large bowl.
Mix a peat moss-based potting mix with sand or gravel if you are growing desert varieties of cactus. Use two parts sand or gravel and one part peaty potting mix and combine them in a bucket or large bowl.
Combine peat moss, vermiculite and perlite for cactus such as agave and aloe, which require very dry soil. Mix one part peat moss, two parts vermiculite and two parts perlite in a bucket or large bowl.