What makes a cactus a cactus?
All cacti are succulents, but most succulents aren’t cacti. Cacti are one plant family. You can tell them apart by their areoles: small, often fuzzy bumps along the stem. Spines, flowers and new stems all grow from areoles.
Some spiny plants look like cacti but aren’t. Pencil cactus is a euphorbia: it has no areoles and bleeds a milky, irritating sap when cut. Most cacti have clear sap. Aloes and agaves have spiny leaf edges, but no areoles.
Desert cacti
These are the round, columnar and paddle-shaped cacti most people picture, from dry parts of the Americas.
- Light: as much as you can give them. A sunny window, or outdoors in summer. Ease them into strong sun to avoid sunburn.
- Water: soak the soil, then let it dry out completely. In winter, water very little or not at all while they rest.
- Soil: very gritty and fast-draining, in a pot with a drainage hole.
- Flowers: many desert cacti flower best after a cool, dry winter rest, in a bright spot.
Forest cacti
Some cacti come from tropical forests, where they grow on trees and mossy rocks. The best known are the holiday cacti, like the Christmas cactus. They have flat, leaf-like stems and few or no spines.
- Light: bright, indirect light. Harsh sun can scorch or redden them.
- Water: more than desert cacti. Water when the top of the soil is dry, not the whole pot.
- Soil: chunky and airy, like an orchid or cactus mix with bark.
- Flowers: many need long, cool nights in autumn to set buds.
The two kinds are easy to mix up, so check which one you have before you change how you care for it.
Handling spiny cacti
- Use thick gloves, or wrap the cactus in a band of folded newspaper or cardboard to hold it.
- Kitchen tongs help when repotting small cacti.
- Watch for glochids. Prickly pears and some other cacti have tufts of tiny, barbed hairs called glochids. They come off at a touch and are hard to see. Lift them out of skin with sticky tape, then tweezers for any that are left.
- Water the soil, not the plant, so you don’t have to reach in among the spines.
Watch out for
- Soft, brown or black patches near the base usually mean rot from too much water. Cut away the rotten part, or take a healthy top cutting, and let it dry before replanting.
- A cactus that grows thin and pale at the top needs more light. The narrow growth won’t fill out, but new growth in better light will be normal.
- Corky, tan patches low on the stem are often normal aging on older cacti, as long as they’re hard and dry.