Q. Why are there discoloration and spots on my cactus plant?
A cactus may develop soft, discolored growth when there is too much humidity and poor air circulation. You can lower humidity levels with a small fan placed in the general area to push air around the room, but not directly on the plant. Also, keep cacti away from high-humidity plants.
Brown, black or yellow spots that are blistered or damp with yellow margins can be a sign of fungal or bacterial invasion caused by poor air circulation, overwatering, low temperatures, high humidity, or low-light conditions. When watering cacti, let the soil dry out before watering again. During warm season growth, water thoroughly. Remove any water that stays in the saucer for more than an hour. Infected areas on the plant should be removed with a sterile tool and then may be sprayed with a safe fungicide.
Although cacti and many succulents like the bright conditions of a southern exposure, too much light can cause bleached-out spots on more tender succulents. Some succulents need shade (eastern exposure) and protection from direct summer noonday sun. Turn plants every few days so the light reaches all areas for even growth; however, don't turn during bloom time or when buds are first forming.
Succulents like temperatures of 75-85°F daily with a 10° drop at night.
There are over two thousand known species of cacti in shapes and sizes from 1 inch to 50 feet tall.
For tips on a variety of gardening topics, see our Plant Information Guides.
- Courtesy of NYBG Plant Information Service