Why are My Cactus Spines Turning Black?

You do your best to take care of your cactus only to see that you have black spines on your cactus. In most cases, you don’t have to worry if you see your cactus spines turning black. 

Why are my cactus spines turning black? Certain species do this naturally after rain, but you should beware of damp environments. For example, the morning sprinkler routine can add extra dampness to the soil, which causes root rot. That can kill your cactus if it goes on for too long.

The Rain Causes Black Spines

In most cases, you don’t have to worry about black spines on your cactus. With some species like the Saguaro cactus, the monsoon rains can cause your cactus to have black spines. You don’t have to worry about it because the cactus spines will return to their normal color after the spines dry.

You do have one thing to be aware of, however. For cases where you live in a damper environment, such as Seattle, you might want to bring your cactus inside because it won’t take the constant rains. Sooner or later, root rot will form, which kills the cactus.

You have other cases where a cactus might have brown spines. That usually happens when you go too long in between waterings. You need to put the watering can over your cactus more frequently.

How to Water Your Cactus

After a good watering, the cactus will usually exhibit black spines. You don’t have to worry too much about it except in rare cases like where the water continually dampens the soil. When you water the cactus, you want to soak it thoroughly, but you need room for dryness. 

In the desert, rains usually happen as torrential downpours. That means heavy downpour will soak your cactus. Then you go for a long period without any rain. You want to mirror this same type of watering as naturally as possible.

While cactus can go for longer than other plants without water, they still need water. 

What Happens when the Cactus Itself Turns Black?

You have cases where the cactus itself will turn black. Usually, this happens because of a bacterial or fungal disease that turns the cactus black. In cases like that, you have to pay close attention. Black spines on a cactus usually aren’t serious, but when your cactus turns black, you will want to act fast because necrosis and crown rot follow swiftly.

Remove the black parts of the cactus with either a gardening knife or shears.

Remember: Sterilize your excision tool well before and after the pruning because this prevents it from spreading to other plants.

Black Spines Signal the Maturing Process

In most cases, black spines on the cactus don’t mean anything bad. Usually, changing colors of the cactus spines mean that the cactus has begun to mature.

Be careful, however, if you decide to transport the cactus from its current pot during this process. Gardeners kill more cacti through transplanting the adults than with any other part of the process. When you transplant the cactus, check to see that you do it on its sunny side. You don’t want to change this because that can kill your cactus.

If your cactus currently receives little sunlight, beware of exposing it to sunlight all at once because this can give it sunburn. Yes, that happens for plants as well. You want to ease your cactus into direct sunlight. That way it doesn’t lead to black spots on your plant.

Black Spines vs. Black Plant: The Difference

You don’t have to worry too much if your cactus has black spines because cactus will usually have black spines when wet. Their color will change more to dull gray when dry. Don’t worry too much.

A black plant, on the other hand, requires your immediate plant care. It indicates that your cactus might have necrosis or crown rot. Crown rot is especially treacherous because of how you can’t get it out of the soil. To get rid of crown rot, first, you cut the top of the cactus off using a sharp gardening knife.

Cut two inches above the black rot at least. The infection usually extends much farther than what you see on the surface. You will leave the spot to dry for between 24 to 72 hours.

Next, you will replant the cactus. Remember, you need to replant it because you can’t get crown rot out of the old soil. It will remain. Empty out the old pot and wash it well with soap and warm water to kill off any bacteria left behind. Don’t use regular potting soil because it holds too much water for cactus and will cause root rot.

Cactus Spines Range in Color

You don’t even necessarily always have black cactus spines. The spines on the cactus grow from a specialized area that botanists call areoles. Occasionally, you will hear it called spine cushions. Depending on the species of cactus, the spines can turn black, orange, pink, red, yellow, gray or white.

While some spines don’t hurt, the most dreadful type is known as the glochids, which you can find on the prickly pear cactus.

Why Do Cactus Spines Change Color?

The thickness and color of a spine depends on its age. Newer spines will always be thicker and have a deeper color than older cactus spines. For soil with a high humus content, you will notice the spines closer to the soil as a brown color. In other cases with brown spines, the cactus died, and it will start to move from the bottom up.

Most of the time, you don’t have to worry about the cactus spines as they change color. Especially if you just watered your cactus, black spines are common afterward. It depends on the species because some cactus spines will turn black after watering, and you have other spines that will change to other colors.

2 Replies to “Why are My Cactus Spines Turning Black?”

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