Why Is My Cactus Turning Black? 7 Reasons & How To Fix It

Cactus is a fantastic choice for beginner and busy gardeners since it requires little care.

Cacti come in various stunning colors, from eye-catching shades of yellow, red, pink, and orange to classic green, but you’ll never find them in black.

If you detect any black spots on your plant, it’s often a considerable concern. We’re here to help you answer the question, ‘why is my cactus turning black?’. Scroll down slowly, so you don’t miss important information!

Why Is My Cactus Turning Black?

why is my cactus turning black- Dark cactus is a common phenomenon Dark cactus is a common phenomenon

The cactus turns black because of some causes such as bacterial and fungal diseases, freezing temperatures, incorrect watering, insufficient lighting, improper feeding, soil diseases, and no ventilation.

Let’s analyze the reasons in detail through the content of the section below. Thereby you better understand why your cactus can turn black and take appropriate measures.

Bacterial and Fungal Infections

The reason for your cactus plant turning black is that it reacts to bacterial or fungal diseases. There are some types of bacterial diseases that you need to check for.

For example, bacterial necrosis can cause your cactus plants to grow black spines. Only particular cactus species have to worry about it.

Fungal infections may take a few weeks to show symptoms. That means your plant may have suffered from an illness before it started showing signs.

Besides, crown rot may also cause many harmful impacts on plants, including black spots. It’s another sort of fungal disease you should pay attention to.

It occurs when fungi in the soil infect your cactus plant, and it has more chance to happen if your soil is too moist since you water the cactus plant too often.

Freezing Temperatures

It’s famous knowledge that cacti prefer dry environments and warm temperatures.

Winters and drastic temperature changes in several regions could stress your plant into changing to black, making their spines become darker or fall off.

Low temperatures may also cause some branches to fall off and the plant to die gradually. If you detect dark spines in your plant that look dry during winter, freezing temperatures must be the prime culprit.

Underwatering & Overwatering

why is my cactus turning black- Improper watering can cause your greens to darken Improper watering can cause your greens to darken

Another reason for a cactus turning black and soft is that you’ve probably overwatered it, causing the roots to get rotten.

In this case, the leaves at the plant’s bottom will become darker before the upper leaves. Root rot happens when the plant sits in excess humidity for an extended time. You can touch the black parts on your cacti to check if they feel soft.

Typically, succulents hold excess moisture in their stems, leaves, and roots. Thus, their leaves will burst and swell if you’ve overwatered them.

On the other hand, a cactus can develop and stay fresh for an extended period without water doesn’t mean it never needs water.

If you ignore the watering for too long, your succulent’s root may collapse and rot once exposed to moisture.

Many gardeners wonder if it’s possible to water their greens after applying liquid fertilizer.

Too Much Sun & Not Enough Light

Like when our skin darkens as exposed to harsh sunlight, cacti can have a sunburn and grow darker spots if you put them under the sun for too long.

Before growing entirely-blown sunburn, cacti’s leaves may turn from natural green into yellowish first, then darken.

Touch the dark-colored parts on your succulents and notice the texture. The sunburn is probably severe, and you can’t do much to fix it if the texture feels scarred or rough.

Meanwhile, if you identify dark spots on top of the plant, there’s a high chance it’s suffering from a light deficiency.

Insufficient light could develop dark-colored parts on the top of your succulent since it is striving to adapt to the little amount of sunlight.

It’s crucial to note that cacti need much sunlight to thrive. If they don’t receive enough, they will show different signs, including dark parts.

If your plants grow taller and thinner than usual while developing in one direction, it’s craving sunlight.

Over-Fertilizing & Lack of Nutrients

why is my cactus turning black- An overabundance of nutrients may cause counterproductive effects An overabundance of nutrients may cause counterproductive effects

Cacti sometimes signal to their growers that they’re overfeeding by showing dark-colored spines.

This succulent species prefers a nutrient-poor substrate to a rich one. The best soil for it is one correctly amended with organic fertilizers without excessive nutrients.

Moreover, excessive nutrients could kill the plants since unnecessary fertilizers in the soil might pose dehydration to them.

On the other hand, nutrient deprivation in the substrate is also an apparent cause of falling and dark-colored spines and stunted growth. If you don’t feed your plants properly, they can even die.

So, have you not fertilized them for an extended time? Then the possible conclusion is that nutrient deprivation is the cause of dark parts on them.

Soil Disease

Sometimes, you may detect yellow mold in your substrate beside the growing black areas. Why does your plant’s soil have yellow mold?

Before solving that question, you need to answer these first: How long has it been since the most recent time you changed the soil and repotted your cacti? Did you grow a new plant in the soil where one previously died?

Though this succulent is hardy and easy to maintain, they are prone to many diseases. One of the prominent signs of diseased cacti is fungi developing on it and molding in the substrate.

No Ventilation

It’s vital to pay attention to ventilation if you’re taking care of indoor cacti. Without appropriate ventilation, the moisture in the room may reach a higher level, which can damage your houseplants.

Just like overwatering, high humidity could kill the greens, and the first sign you notice is cactus tips turning black, particularly in spines and branches.

If your indoor cacti and other plants in a packed garden grow more dark parts than solitary or outdoor cacti, that’s the most significant evidence that ventilation is the prime cause.

Don’t forget that this succulent is a desert plant, so it naturally thrives in environments with low humidity levels.

How To Save A Black Cactus?

Though your cactus turned black, don’t feel so depressed. It’s worth making some effort to save it since there’s still a chance things can turn around.

Isolate The Plant

why is my cactus turning black -Separate the rotted plant from othersSeparate the rotted plant from others

Once you notice black on the cactus, the first step is to separate it from other plants. Even if your indoor farm includes only 3-4 plants, bacterial and fungal diseases can quickly spread to the surrounding.

Note that phyllosticta pad spots can spread through the water or wind, so you’d better not put other healthy greens at risk.

Remove Damaged Parts

Because the disease will develop without intervention, it’s crucial to block it from the beginning. That means eliminating the affected parts of your cacti.

Cut all the black branches and spines with a small knife or pruning shear. Fungal infections can reach remarkably deep, so cut until you no longer see rotten spots remain. Infection and rot will badly affect your greens internally and externally.

Examine the Root

Check the roots to see if there’s any damage. This step is essential if you’re searching for the root cause of dark spines on your greens.

Look for affected roots that appear more dark-colored than others. Rancid roots may be stinky, or you may find fungi and mold developing on them.

If you identify any, prune off those roots and wash the healthy ones with clean running water.

Perform A Soil Change

why is my cactus turning black- Diseases may linger in the soil and continue developingDiseases may linger in the soil and continue developing

Crown rot and other diseases can remain in the soil even after cutting off all infected branches. If you don’t treat the soil properly, the succulents will likely suffer from the disease again.

Even though you don’t see any sign of bacterial infection, changing the substrate and adding more nutrients to your new potting substrate is still a good idea.

If it’s your first time repotting cacti, watch this video for some easy tips before starting:

Cut Again if Necessary

You might have missed some tiny rotted and black areas during the first trimming turn. Those remaining parts can affect other healthy areas and cause your greens to start rotting again.

So, you should re-check your plant to see if any rancid spots are left. And don’t forget to disinfect the knife or shears after pruning to eliminate the chance of diseases spreading to the surrounding area.

Water The Plant Properly

Overwatering can pose the same harm as underwatering, and dark branches can start forming due to inappropriate watering routines.

Hence, plan your watering schedule properly while taking care of your garden.

This practice is paramount since you can help the plants grow stronger and thrive again.

Maintain Adequate Temperatures and Sunlight

If you grow your greens indoors, it’s advisable to keep the shutters or windows shut throughout colder months.

It’s best to maintain the thermostat put in the room at about 23.9 to 26.7°C (75 to 80°F) during winter to make your succulents comfortable.

A problem with caring for houseplants is the lack of natural sunlight. Ensure to provide the cactus with at least six hours of natural light daily.

If you live in a subtropical region or where the sun is very harsh in the afternoon, you can apply some methods to cover your cacti. Still, ascertain that they receive enough morning sun.


Something must have gone wrong if you detected black spots on your cactus. That’s when you need to research or ask other experienced growers this question: why is my cactus turning black?

We’ve mentioned some issues your succulents may have experienced, which induce dark-colored parts to show.

We hope you’re well-equipped with helpful knowledge and tips for saving your plants. See you in the next article!

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