Over-Watering Diseases of Succulents

Stem and Root Rot

• Over-watering succulents causes roots to decay, setting the stage for the fungal pathogens that cause stem and root rot. Pythium rot -- along with a similar disease, phytophthora rot -- is indicated by discolored, mushy leaves and stems; in severe cases, the plant becomes pulpy and collapses in on itself. There can also be a ring of brown or black around the stem near the soil line; upending the plant reveals brown or blackened roots. Rhizoctonia rot is indicated by discoloration proceeding upward from the stem base; gray, cobwebby strands on the surrounding soil help to confirm the diagnosis. To prevent spreading infection to other succulents, dispose of the affected plants, along with their soil. In cases where only a few roots are affected, salvage might be possible. Clemson Cooperative Extension suggests snipping off the blackened roots and repotting the succulent in new soil.

Powdery Mildew

• Powdery mildew, caused by the Oidium fungus, also can be triggered by over-watering. Symptoms include a white, powdery growth on the upper sides of the leaves, along with brown, papery spots. Promptly trim away all infected leaves, and water the plant less frequently. Colorado State University advises treating powdery mildew with neem oil; you can also use a commercial fungicide every seven to 14 days. Follow the manufacturer's directions for amounts.

Proper Watering

• To avoid over-watering succulent houseplants, allow soil to dry thoroughly between waterings. Then water thoroughly, irrigating the plant until water comes out the drainage holes. Empty the overflow saucer properly. For outdoor succulents, the University of Arizona Cooperative Extension advises watering every 10 to 14 days, after checking the root zone 2 to 3 inches below the soil line. If it is even slightly damp, postpone watering until it dries out. When nighttime temperatures fall below 60 degrees Fahrenheit, refrain from watering; the plants should survive on natural rainfall.

Prevention

• Providing proper conditions helps your succulents resist disease. Succulents and cacti need abundant light; a bright, sunny windowsill is ideal. You can augment natural light with a fluorescent tube, located 6 to 12 inches above the plants; it should be on for 14 to 16 hours a day. Succulents also need well-drained soil; all pots should have drainage holes. Inspect succulents often for signs of disease and weakness. Be alert for plants that haven't shown new growth, that are not optimum in color or appearance or don't seem firmly rooted in their pots.