Why is My Cactus Turning Black?

Oh, no! Your cactus has started to turn black! You have to act fast because once the cactus turns black, you have a high chance of it dying. In many cases, it is too late. Act immediately. In many cases, you can’t save it, but you do have actions that could save it.

Why is my cactus turning black? Cactuses often turn black because of overwatering. Overwatering ranks as the number one cause of death. The overly damp soil nurtures an environment for fungal diseases which include necrosis, phyllosticta pad spotting and crown rot.

Not Enough Light

Discoloration of any kind on your cactus could indicate that it gets too little light. You can tell your cactus is healthy when it has a deep green color. Unhealthy cactus will have a faded color, which can eventually turn it black. You have to identify the cause and take care of it as soon as possible.

While you can get too little light, you should understand how your cactus can get too much light. In particular, be cautious of moving a cactus from low light into bright light abruptly. You want to transition it slowly. Cactus that get exposed to too much light can turn orange, yellow or they might even have a bleached appearance.

Rotting Cactus

When the soil holds the dampness and water, the cactus’s roots may rot. Cactuses primarily live in the desert, and their root systems have evolved to know feast or famine. Less than 300 mm of rain occurs each year in the desert. When it rains in the desert, flash flooding becomes a real threat, and the rain drowns the cactus in torrential downpours. Nevertheless, the cactus has adapted to such rains and because the sand doesn’t hold water for long, cactuses do well with it.

Cactus Black at the Top

A cactus that starts to get black and mushy at the topmost likely has a condition known as tip rot. Act as soon as you spot it because the rot will quickly spread throughout the cactus to kill it. Cactus that rots from the tip down can’t be stopped once it picks up momentum.

What Causes Rot at the Top?

Anything from fungus spores to disease to pests could cause the cactus to rot at the top. Cactuses that suffer damage have a greater vulnerability to disease and fungus. In some cases, water will set in the wound, and this can initiate the process of cactus rot. You most likely will never understand the exact causes, but luckily, the steps to save a cactus that turned black is the same.

Saving a Dying Cactus–Step #1: Prune off the Rot

You must extract the black parts of the cactus entirely. Leave nothing of the rot on the cactus, or it can spread to kill your cactus. Remove the rot 1 inch below into the healthy green tissue because the rot often spreads farther underneath than what it shows.

You want to take the pruners and make sure that you have cut away at all the rot on the cactus. You can use a knife to remove the rot.

Expert’s Tip: As you cut away at the black rot on the cactus, beware of getting the milky latex close to your eyes. It stings if it gets in the eyes.

Step #2: Sterilize the Tool Used


Whether you use a pruner, shears or knife, you must sterilize the tool. This prevents the spread of disease when you use it later. You might sterilize the tool in rubbing alcohol. Anything over 60 percent alcohol will kill off the fungus and disease on the tool.

Step #3: Prune away the Rot Layer by Layer


You want to cut away at the rot layer by layer. Check to see that you removed all of it. As you prune away the cactus, you might see rot on it. Continue to prune until you arrive at a point where no further black spots on the cactus exist. The spots could be black, brown or yellow.

Make sure that you remove it all because even the tiniest bit of rot left behind means that the rot continues to spread. The signs of rot include blackness, mushiness, brown cactus or a soft cactus.

Expert’s Tip: After you have made the cut, you can sprinkle calcium on the cut. The calcium moderates the soil acidity, and at the same time, it provides the plant with the essential nutrients needed to survive.

What to Keep in Mind: Let’s say that your cactus will sit in the garden outdoors. If this is true, you will want to cut the cactus at an angle because it eliminates the possibility that water can settle on the cactus and cause rot. Until the incision heals, you will want to move the cactus to a safe and dry space. You will know when it has healed because the region callouses over.

Beware of Black Spots on a Cactus


If your cactus starts to rot, you need to respond immediately. Cactus rot can kill your cactus, but it can spread to the surrounding plants as well. A cactus turning black on the bottom has a low chance of survival if you don’t respond right away. If you notice sunken spots, scabs or soft areas, don’t wait to take care of it.

Extended Breezes Can Hurt Your Cactus


Lengthy cool breezes can negatively impact the health of your cactus. You must respond fast if you notice a draft because this can cause your cactus to turn black. They will feel it even when you can’t in some cases. Like with a frost or too much heat from the sun, it can have a negative impact on your cactus. Still, don’t worry about a ceiling fan. In many cases, cactuses will benefit from the air circulation.

What Happens if My Cactus Spines are Turning Black?


Unlike when the plant itself turns black, black cactus spines should not be the cause of worry. I’ve already written a great article on this here. Usually, black cactus spines happen because the needles have become saturated with water. You especially notice this phenomenon after you have watered your cactus.

How to Deal with Cactus Black Spots


Like with a cactus that has begun to turn black, you must act fast to stop the spread of black spots. This is the same thing as when your cactus starts to turn black. In some cases, if black spots have only begun to form, you could still stop them. Usually, cactus black spots will indicate that the cactus has a fungal infection.

As it is when your cactus turns black, you need to remove the black spots with a knife. Don’t leave anything remaining. Better to cut away too much than too little because even a hint of remaining blackness in the cactus can start the killing process over again.


Hopefully, you have learned more about how to deal with black spots on your cactus and what causes it. In many cases, you won’t know the cause. The process of eliminating it remains the same either way. Understanding the cause, however, can help you to avoid making the same mistake in the future.

2 Replies to “Why is My Cactus Turning Black?”

  1. Pingback: Why is My Cactus Turning Pink? | Dream Plants!
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