Why Is My Cactus Turning Black?

Cacti come in various shades; however, black is not one of them. So, if you see a cactus turning black, it is generally not a good sign. It means that the plant is not healthy and undergoing some sickness. Thus, preventive steps need to be taken to ensure that the cactus does not die.

Why Is My Cactus Turning Black?

The following are some of the common reasons which lead to the browning of the cactus

  • Over Watering
  • Frost
  • Bacterial Infections
  • Pest Infestation

1. Over Watering

Overwatering the cactus makes it turn mushy and soft . It will also lead to stagnation of water, which would eventually cause rotting in the cactus and make it prone to deadly diseases like root rot. Thus, making it turn black.


The overwatered cactus must be allowed to dry before being watered again. The roots should be checked for infections such as root rot, if affected, the infected root must be trimmed immediately. The root should be treated with fungicide before being re-potted with fresh, sterile soil.

2. Frost

Excessive frost can cause severe internal damage to the cactus. It happens when the plant is left outdoors in extreme cold, causing the cells to rupture. The plant tries to self-heal by creating calluses over the damaged areas, thus, making it look blackish-brown.


Cacti do not do well in freezing temperatures. The cactus should not be exposed to temperatures below 10 °C for an extended period. Thus, the plant should not be kept outdoors in freezing winters. Similarly, placing the plants near open doors and windows should be avoided. If exposed, the affected cactus must immediately be moved to warmer temperatures to avoid permanent damage to the plant.

3. Bacterial Infection

If the cactus starts turning black from the top , it generally is a sign of crown rot. Crown rot is a deadly fungal infection that tends to attack the roots of the plant and makes it turn black. It is generally caused by overwatering or the use of infected soil.

Another fungal infection that is found in certain cactus species is bacterial necrosis. It causes blackened spots on the plant that spread to form deadly necrotic pockets.


The first step is to isolate the affected cactus . Thereafter, the damaged spots need to be detached from the cactus using a sterilized knife. Then the cactus needs to be re-potted in fresh, sterilized soil.

4. Pest Infestation

Different types of pests and parasites can affect the cactus and cause it to blacken. Such as tiny brown bugs called scales that feed on the essential juices of the cactus and leave a honeydew-like substance behind. This substance causes a black sooty mold which makes the cactus appear black.


These pests can severely weaken the plant and can affect its health. To get rid of scale bugs, the affected area should be sprayed with oils such as neem or rubbing alcohol once a week. The infested plant needs to be isolated immediately and kept separated until the bugs disappear. The healed plant should be re-potted with fresh, sterile soil before being introduced to the other plants.

So, these are some of the steps that could help you nurture a blackening cactus back to health.

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