A common misconception is that only the worst gardeners can kill a cactus. As hardy as these plants are, they still need care and maintenance like any other plant. If you're noticing discolouration, drooping, leaf drop or other signs of wilting on your cactus, you may have some care or infection problems that must be addressed to keep the plant blooming to its best levels.
Knowing how often to water a cactus is difficult, and too much water, as well as not enough water, can each cause their own drooping and wilting problems. The traditional thought of cactus is of a plant that grows in desert conditions, but some species of the plant grow in sheltered woody areas as well and so need more water to survive. Understand what type of cactus you have before trying to grow it so that you understand its watering needs. Over- or under-watering can cause rot problems, dryness and drooping or dropping parts of the plant.
Curing Watering Problems
As a general rule, the most important aspect of cactus care is to use cactus soil, which drains quickly. Any cactus species sitting in stagnant water will develop rot problems. Repot the cactus in a fresh pot filled with new soil once per year to keep the soil fresh and fungus free. As for watering, add water to your cactus any time the top 2 inches of water feels dry to the touch. Stop watering as soon as you see excess water start to drain from the drainage holes in your planting pot. The desert cacti will need to be watered this way far less frequently than the others.
Insect infestations on your cactus plant can also cause serious drooping appearance and the potential death of the plant. A bug nesting on a prickly cactus may seem unlikely, but small insects can inhabit the spaces between the spines and may live on some of the gentler cacti species. Common cactus bugs include scale and mealybugs; both of these types of insects feed on the cactus leaves and stems, eventually draining all of the nutrients and killing the plant.
Curing Insect Problems
Rub down the exterior of your cactus with cotton swabs or rags dampened in rubbing alcohol; avoid those prickly spines. This will either suffocate or drive away most insect species. If you can identify which type of bug has infested your cactus, find an insecticide at a garden centre or nursery that will treat your specific insect. Otherwise, a general houseplant insecticide will cure most infestations.