Cactus and Black Rot

Diseases

• Most cacti diseases are the result of improper watering techniques or exposure to humid conditions. Rots and molds range in color from yellow to orange to gray to black. Unfortunately, black rot at the base of a plant cannot be cured or contained. If your plant exhibits a slick, black legion or legions at its base, your only option is to discard it, determine the cause of the disease and buy a new plant. Yellow stem lesions that turn brown are also incurable and result in plant death.

Watering

• Indoor conditions vary greatly, as do container size and type of plant, but a few watering rules suitable for every situation include these: Water infrequently but deeply. This type of watering mimics the cactus' natural environment. Infrequent, shallow watering causes root damage and lackluster growth. Deeply water the plant during the growing season, spring and summer when the top 1/2 inch of the growing medium is dry. During the dormant season, occasionally water the plant but do not saturate it. Fertilize with a low-nitrogen fertilizer or specialty cactus fertilizer during the active growing season. By following a good water and fertilization schedule, your cacti should maintain its health and become less prone to rot and disease.

Planting

• Allowing your cacti adequate drainage as well as room to grow are essential elements in avoiding rot and moisture-caused damage. Soil mixes should contain 1/3 part sterile garden soil, 1/3 part peat moss and 1/3 part coarse sand. The soil provides organic matter, peat moss retains needed moisture and coarse sand allows drainage. Commercial specialty cactus potting mixes are also available. Some succulents and tropical plants, like Christmas cactus, benefit from additional organic matter and fertilization. Repot your cactus as needed, usually when the plant's width is within 1/4 inch of the container's sides. Repotting prevents root damage and soil compaction.

Considerations

• Cacti that exhibit orange, yellow or gray molds and rots can be treated and may ultimately recover from their conditions. Brown spots develop when plants are exposed to humidity and over-watering. Remove the plant from humidity, and avoid watering until the soil dries and the plant should recover. Soft rot and gray mold on upper portions of the plant can be controlled by removing, or cutting out, the damaged area.