Cacti are a diverse group of plants known for their distinctive forms and resilience in harsh conditions. These resilient succulents have gained popularity as low-maintenance houseplants. This guide explores cactus characteristics and provides practical advice for their care, repotting, propagation, and common issues.
Understanding Cacti
Cacti are distinguished by areoles, cushion-like structures on their stems from which spines, flowers, and new branches emerge. While many succulents store water in their fleshy tissues, areoles are exclusive to the cactus family. Most cacti have spines instead of leaves, which protect the plant, provide shade, and reduce water loss in arid environments. Their thick, fleshy stems store water, enduring long periods without rainfall.
Cacti fall into two categories: desert and forest cacti. Desert cacti, the most recognized type, feature prominent spines and thrive in bright, direct sunlight (e.g., barrel cactus, saguaro). In contrast, forest cacti (e.g., Christmas cactus) are typically epiphytic, growing on other plants rather than in soil. These varieties often have softer bristles or are spineless and prefer filtered bright light.
Essential Cactus Care
The right environment is essential. Most desert cacti require bright, direct sunlight for at least six hours daily, making a south-facing window an ideal indoor location. Forest cacti, however, prefer bright, indirect or filtered light. If natural light is insufficient, grow lights can supplement their needs.
When watering, the “soak and dry” method is recommended. This involves thoroughly soaking the soil until water drains, then allowing it to dry completely before the next watering. Overwatering can lead to root rot. During their active growing season in spring and summer, cacti need more frequent watering, perhaps every 2-4 weeks. In fall and winter dormancy, watering should be significantly reduced, possibly to once a month or less.
Cacti require a fast-draining potting mix to prevent water from sitting around their roots. Regular potting soil is unsuitable; it retains too much moisture. A specialized cactus or succulent mix, containing inorganic materials like perlite, pumice, or coarse sand, ensures proper drainage and aeration. Terracotta pots are preferred due to their porous nature, allowing excess moisture to evaporate.
Cacti tolerate warm temperatures, but many desert varieties benefit from cooler temperatures during winter dormancy for optimal flowering. They prefer low humidity, consistent with arid habitats. Fertilizing is done during the growing season (spring and summer) using a diluted, cactus-specific fertilizer.
Repotting and Propagation
Repotting is necessary when a cactus becomes root-bound, roots emerge from drainage holes, or the soil degrades. A general guideline is to repot every two to four years. The best time for repotting is during the active growing season, from late March to early September. When repotting, select a new pot only one size larger (typically 2-5 centimeters wider in diameter).
To safely repot a spiny cactus, use thick gloves, a folded newspaper, or a tea towel to protect your hands. Gently remove the cactus from its old pot, loosening compacted soil around the roots. Place it in the new pot at the same depth, filling around the roots with fresh cactus potting mix. Do not water the freshly repotted cactus immediately; allow it to adjust for about a week before resuming regular watering.
Cacti can be propagated through offsets (pups) or stem cuttings. Offsets are small plantlets that grow from the parent plant and can be twisted or cut off. For stem cuttings, a healthy stem should be cut cleanly. After removal, both offsets and cuttings should form a callus, a dry, hardened layer over the cut end, before planting. This callusing process (a few days to several weeks) prevents rot when introduced to soil. Once callused, plant the offset or cutting in well-draining cactus soil, inserting the base deep enough to stand upright. Avoid immediate watering; mist the soil lightly until roots establish (typically four to six weeks).
Common Cactus Problems
Despite their hardy nature, cacti face several common issues. Overwatering is a frequent problem, leading to root rot. Symptoms include yellowing, mushy stems, wilting, and black spots, especially at the base. If overwatered, stop watering, allow the soil to dry, and if severe, repot into dry, well-draining soil after removing soft, mushy roots.
Underwatering causes symptoms like shriveling or stunted growth. The cactus may appear deflated but often plumps back up after thorough watering. Adjusting the watering schedule to be deep but infrequent can resolve this.
Pests such as mealybugs and spider mites can affect cacti. Regular inspection helps identify these insects. Treatment involves isolating the affected plant and using rubbing alcohol or insecticidal soap to control the infestation.
Etiolation, characterized by thin, leggy, pale growth, occurs when a cactus does not receive sufficient light. This stretching indicates the plant seeks more intense light. While etiolated growth cannot revert to its original thickness, moving the cactus to a brighter location (e.g., south-facing window or grow lights) can encourage healthy new growth. Severely etiolated parts can be pruned.
Sunburn or scorching results from sudden exposure to excessive direct sunlight. Symptoms include yellow or white patches that may turn brown. To treat sunburn, move the cactus to a shaded area immediately and gradually reintroduce it to brighter light over several weeks.