Cacti come in two types, forest-dwellers and desert-dwellers, and their cultural requirements are very different. Desert cacti don't need leaves for photosynthesis and can get enough light through their stems alone. Instead of leaves, such cacti have spines (figure A), which protect the stem from invading animals and insects in search of water. Overwatering is the most common cause of death for indoor desert cactus plants. During their growing period, such cacti need water no more than once every week or two. They need almost no water during their dormant season (figure B). You can encourage dormancy by withholding water for three to four months. The plant may reward your efforts by blooming. How do you know when it's time to water? Watch the national weather forecast, and when it rains in Tucson, water your cactus. Cacti need fast-draining soil, and special soil mixes are available at garden centers and nurseries. These mixes contain sand and other quickly draining materials necessary to keep the roots healthy (figure C). If you like, you can make your own potting mix at home from the following ingredients: 1 part peat moss
1 part builder's sand
1 part perlite (figure D)
1 teaspoon slow-release fertilizer such as Osmocote
3 tablespoons ground limestone. Plant your cactus with the root ball showing slightly above the surface of the soil.
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