Even resilient cacti can encounter problems that affect their health. Understanding common issues allows for timely intervention and helps maintain their unique beauty. While often perceived as low-maintenance, cacti still require specific care to prevent various ailments. Early identification of distress signs is important for successful treatment.
Watering Problems
Overwatering is a common cause of distress for cacti, leading to mushy stems, discoloration, and eventual collapse. This occurs with too much water or poorly draining soil, often resulting in root rot. Signs of root rot include soft, black, or foul-smelling roots, and yellow or brown discoloration at the plant’s base. To address this, carefully remove the cactus from its pot, shake off excess soil, and trim away any soft, discolored roots with clean, sharp scissors. Allow cut areas to dry and callus for several days in a bright, airy location before repotting in fresh, well-draining cactus soil.
Conversely, underwatering also harms cacti, causing them to shrivel, wilt, or appear hollow. This indicates insufficient moisture, and the plant’s tissues become soft and wrinkled. If mildly shriveled, a thorough watering may suffice. For severely dehydrated cacti, soaking the entire pot in a basin of water for approximately 30 minutes allows the plant to absorb moisture more effectively. After rehydration, ensure the soil dries completely between subsequent waterings to prevent recurrence of either issue.
Pest Infestations
Cacti can attract specific pests, despite their protective spines and waxy surfaces. Mealybugs appear as small, white, cottony masses often found in crevices or at the plant’s base. These insects feed on plant sap, leading to weakened growth and sometimes a sticky residue called honeydew. Remove mealybugs by dabbing them directly with a cotton swab dipped in rubbing alcohol, or by spraying the plant with a dilute alcohol solution (1:3 alcohol to water).
Spider mites are tiny pests that cause fine webbing on the cactus, accompanied by stippling or discolored spots on the plant’s surface. These mites thrive in dry conditions; address infestations by washing the plant with a strong stream of water or using insecticidal soap. Scale insects manifest as small, hard, dome-shaped bumps on stems or pads, often resembling part of the plant itself. They also feed on plant juices, causing wilting or yellowing. Manual removal with a fingernail or tweezers is effective for small infestations, while a systemic insecticide or insecticidal soap can be used for widespread problems.
Environmental Stressors
Insufficient light, known as etiolation, causes cacti to stretch and grow thin, pale, or elongated. This irreversible growth indicates the plant is seeking more light. To prevent etiolation, move the cactus to a brighter location, ideally one offering several hours of direct sunlight daily for desert varieties. If natural light is limited, particularly indoors, supplementing with a grow light provides the necessary intensity.
Conversely, too much direct light can lead to sunburn, manifesting as yellowing, browning, or bleached patches on the cactus’s surface. This damage impairs the plant’s ability to photosynthesize. If sunburn occurs, move the cactus to a location with bright, indirect light or provide partial shade. Gradual acclimation to new, brighter environments is necessary to prevent this damage.
Temperature extremes also pose threats. Cold or frost damage can cause blackening, mushiness, or discolored spots on the cactus tissue. This often occurs when temperatures drop below 32°F (0°C). To protect outdoor cacti, cover them with frost blankets or burlap before freezing temperatures. Potted cacti are more susceptible and should be moved indoors to a garage or sheltered area when frost is expected.
Other Common Issues
Cacti can develop fungal spots or diseases, appearing as black spots or corky areas on the plant’s surface. These issues are often distinct from root rot and can be exacerbated by high humidity or poor air circulation. Improving airflow around the plant and ensuring adequate drainage helps prevent these conditions. If severe, specific fungicides may be considered.
Nutrient deficiencies are less common for cacti but can occur, presenting as stunted growth or unusual discoloration. While cacti are not heavy feeders, providing a balanced, cactus-specific fertilizer during their active growing season supports overall health. However, over-fertilization should be avoided as it can harm the roots.
Physical damage, such as scarring from impacts, animal bites, or accidental breakage, can occur. Cacti often possess an ability to heal themselves from such injuries, forming calluses over damaged areas. While these scars may be permanent, they do not compromise the plant’s long-term health unless they lead to secondary infections.