Why is My Cactus Turning Brown? 5 Reasons + What to Do

Cacti are well adapted to dry conditions, and it becomes relatively easy to grow and care for them as houseplants. One thing you cannot ignore is when your cactus is turning brown. It might signify distress from an underlying problem that may harm or kill your plant.

A cactus may turn brown due to overwatering, underwatering, sunburn, poor drainage, pests, and diseases. Corking is also an aging process that may change the color and texture of your cactus to brown and coarse.

Why is my cactus turning brown?

Your vibrant green cactus may turn brown as a result of the following:

1. Cactus corking

Corking is an aging process in plants where stems becomes woody and hard over time. Cactus, in particular, develop a thick outer layer of bark-like tissue. This process protects the cactus from damage and water loss and shows a healthy, mature plant.

However, corking can be triggered by environmental stress from drought, transplanting, frost, or low humidity levels. In such cases, the cork will be produced in areas where it’s more needed.

Sometimes it might be difficult to tell the difference between cactus corking and rot unless you look into other factors, such as the texture and age of the plant. Cactus stem rot is a serious condition that can affect a cactus and cause its stem to become soft, mushy, and discolored.

What to do

There is little you can do once the corking process has started. Providing better care to your cactus is the most important thing to do.

• Provide indirect light and keep the plant away from drafty areas or near heating vents.
• Water the cactus carefully and allow the soil to dry completely before watering again.
• Do not overexpose the corking cactus to frost, as it can damage or kill the plant.
• Minimize moving the plant, especially when wet, as this can damage the woody stems.
• Frequently inspect the plant for pests and provide treatment if needed.
• Repot the plant if the soil or roots are heavily compacted.

2. Cactus rot

Rot is a common problem in cactus plants, and it can occur on any part from the roots to the tip. Stem rot is usually caused by a fungal or bacterial infection, which can enter the plant through wounds, cuts, or damage to the stem.

Stem rot symptoms include the cactus getting soft or mushy, darkened stems, drooping of the plant, and wilting. In some cases, you may notice a foul smell around the plant. The rot may spread to other parts of the plant, including the roots, and can eventually cause the cactus to die.

Root rot is mainly a problem of excess moisture around the roots. It can be caused by overwatering or poor drainage. Root rot is a silent killer and the most difficult to detect and treat. The affected plant may die a few days before you even figure out the solution.

What to do

Cactus rot spreads very quickly and can kill the plant in a short period. However, you can save a rotting as follows:

• Get a sharp knife or pruning shears, and clean and sterilize it. Dirty tools can spread bacterial infections.
• Carefully cut off the rotting part of the cactus in small layers until all the signs of rot are gone.
• Thoroughly wash the remaining plant with clean water. Be sure to cover the soil to avoid overwatering.
• Let the wound dry for two to three days, and repot the cactus in fresh soil if you are dealing with root rot.

3. Sunburn

Although cacti plants are well adapted to hot sunny conditions, some species, like the holiday cacti, won’t take it easy in direct sunlight. They always prefer bright indirect sunlight.

Sunscald commonly occurs in hot, dry weather when the plant is suddenly exposed to direct sunlight, especially after being in the shade for an extended period.

The appearance of brown patches on stems or leaves is a common sign of cactus sunburn. The plant may also shrivel and get droopy as it tries to reduce the surface area for moisture loss. Continuous exposure may result in the plant wilting and drying out.

What to do

To prevent sunburn in new cacti plants, acclimate them to direct sunlight by gradually increasing the amount of exposure over time. Further, provide shade or a protective cover during the hottest parts of the day, especially if the cactus is in a location with intense sunlight.

4. Insect pests

Pests are an occasional problem on cactus plants. Scale, mealybugs, spider mites, and fungus gnats are common insect pests that damage cacti and succulents as they suck the plant’s juice. The bugs hide in tight places where it’s hard to see and reach them.

Their feeding creates wounds that heal into brown scars that distort the cactus’s appearance. Pests are more of a health problem to a plant as they also act as vectors for bacterial and fungal infections.

What to do

Good cultural practices and chemical treatments can help manage pests on cacti plants. In addition to that;

• Grow your cacti and succulents in ideal conditions of light, moisture, and temperature.
• Practice good hygiene by pruning your plants and cleaning the soil and pots.
• Quarantine and inspect new plants before you introduce them into your home.
• Wash pests off the plants using a strong blast of water. Remember to cover the soil with a plastic bag to avoid overwatering.
• You can get rid of mealybugs and scale insects using cotton swabs or a piece of cloth dipped in rubbing alcohol.
• Use insecticidal soap or horticultural oils like neem to treat severe infestations. Be sure to use as directed on the product label and test on a small area before use to see if it’s safe on the plant.

5. Frost damage

Cactus can survive low temperatures but can be damaged with prolonged exposure to frost. The cold tolerance varies from one species to another. Most cacti gradually change to brown or dark during winter as their metabolism activities decline.

Extremely cold temperatures will cause the cactus stems to get soft and blackened, indicating rot. To some point, this is irreversible damage caused to the plant cells. Without interventions, the rot may spread, and eventually, the plant dies.

What to do

You can save your cactus from frost damage by cutting off the damaged parts to discontinue the rot from spreading to other healthy parts. This should typically be done when the frost has ended. Be sure to use clean, sterile tools.

You can protect your cactus from winter damage in several ways.

• Move your cactus indoors and place it in a bright place with free air movement.
• Provide shelter outdoors or use protective covers such as frost cloth and plastic sheets.
• Cover the topsoil with thick organic mulch to protect the roots from freezing.

Final Thought

If you notice your cactus turning brown, identify the cause immediately and take appropriate action to save the plant. Further, ensure it is planted in well-draining soil, water it appropriately (not too much or too little), and watch for any signs of pests or disease.

References:

• Missouri Botanical Garden: Insect pests of cacti and succulents grown as house plants

• “Effects of Cold Weather on Horticultural Plants in Indiana,” by Larry A. Caplan, Purdue University
• Desert Botanical Garden: Prevention and Care of Freeze Damage