Why Is My Cactus Turning White? Here Are the Reasons
White discoloration on a cactus can signal stress, disease, or even healthy aging. Learn to interpret the signs to understand what your plant needs and how to respond.
Noticing white patches on your cactus can be concerning. This change often signals that the plant is experiencing stress from environmental factors, pests, or natural processes. Identifying the cause is the first step toward correcting the issue. This guide will help you diagnose the problem.
Sunburn and Light Issues
A frequent cause of a cactus turning white is excessive exposure to intense sunlight, a condition called cactus sunburn. This appears as bleached, white, or yellowish patches on the side of the plant receiving the most direct sun. Severe exposure can cause the tissue to become hard and scarred, which often occurs when a cactus is moved suddenly into a much brighter environment.
If your cactus shows signs of sunburn, relocate it to a spot with less intense light. An ideal location offers bright, indirect sunlight with shade during peak afternoon hours. While the scarred white tissue will not revert to green, the plant can recover and produce healthy new growth from unaffected areas.
To prevent sunburn, acclimate a cactus to increased light levels gradually. This process, known as hardening off, involves extending its time in direct sun over one to two weeks. Start with an hour of direct morning sun and slowly increase the duration.
Pest-Related Discoloration
White spots on a cactus may be a sign of an insect infestation. Several pests create a white, fuzzy, or speckled appearance as they feed on the plant’s sap. A close inspection is necessary to identify the pest, and you should isolate the affected plant immediately to prevent them from spreading.
Mealybugs are a common culprit, appearing as distinct, cotton-like white masses in the joints between stems or at the base of spines. Another pest, scale insects, are small, hard, immobile bumps that are white or gray. They are often found on the main stems and can be scraped off with a fingernail.
Spider mites are tiny arachnids indicated by fine, dusty, white webbing around the cactus spines and new growth. The plant’s surface may also look stippled with tiny white or yellow dots. For any of these pests, treatment can begin by dabbing visible insects with a cotton swab dipped in 70% isopropyl alcohol. For widespread infestations, spray the plant with insecticidal soap or neem oil.
Fungal Infections
A white coating on a cactus can also be a fungal disease. The most common is powdery mildew, which manifests as white, dusty patches on the plant’s skin. While the spots can be wiped away, the fungus will return if the underlying conditions are not addressed.
Powdery mildew thrives in high humidity and poor air circulation, conditions that can occur indoors during winter or in a terrarium. The fungus spreads via airborne spores from other infected plants, making proper ventilation a primary defense.
To treat powdery mildew, first clean the visible patches from the plant, then apply a fungicide. Improving air circulation is also a necessary preventative measure. This can be achieved by moving the plant to a less crowded area or using a small fan to keep the air moving and the plant’s surface dry.
Natural Corking
Not all white or tan discoloration on a cactus is a sign of a problem; it can be a natural aging process known as corking. This begins at the base of an older, established cactus and slowly progresses up the stem. The affected tissue becomes firm, woody, and develops a tan or whitish, bark-like texture. A primary difference between corking and other issues is that the tissue is hard and solid, not soft or fuzzy.
Corking is a structural adaptation that helps the cactus support its increasing weight as it grows taller and heavier. The plant reinforces its base to prevent it from collapsing, which is a normal sign of maturity for many cactus species. It is not a disease or the result of improper care.
Since corking is a natural process, no treatment is needed. It is important to recognize it so you do not misdiagnose it as a harmful condition and apply unnecessary treatments. As long as the rest of the plant appears healthy and the corked area is firm, there is no cause for concern.