Is your Cactus Turning Black?
Do this QUICKLY to save it!

You've noticed strange black spots on your perfectly healthy cactus. Time is of the essence if you're to save it.

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Kelly Adams

June 27, 2021

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Black isn’t a cactus color. Any spot of it on a perfectly healthy plant is a red flag that should be addressed immediately before it spreads onto the rest of the plant. These marks are caused by a number of issues that will be discussed. Most of these issues occur mainly because of the environment it is provided and we will explain what could’ve gone wrong and how to fix it.

To save our plant and prevent future incidents like this, avoid overwatering, underwatering, or drastic changes in temperature. Invest in fungicide and pesticide, and remove infected areas.

1. Avoid Overwatering

a tilting cactus

Cactus are generally low mintenance plants. Too much water will kill it. If you aren’t allowing your plant’s soil to dry out before the next watering session, it’s possible there was too much water that got caught up in the soil. This creates the perfect environment for moisture, that helps bacteria grow and cause root rot. Usually in this case, it’s too late.

Solution: Check the roots. If they’ve unfortunately all rotted, prepare to propagate your plant in a fresh pot. If not, cut off the root rot immediately and prepare to repot your plant. Do not water them for a good week after that.


It's easier to save a cactus that's rotting from top to bottom, which is why checking for root rot first is important.

2. Avoid Underwatering

dried up soil

In this case, your cactus is still salvageable. Although cactus are low maintenance plants, it doens’t mean zero maintenance. You’ll know if you’re underwatering your plants because the soil will look unceremoniuosly dry and crumbly.

Solution: Letting the soil dry out is great, but be sure to water the plant once that happens or the plant’s roots will starts to die and stop taking in any nutrients.

In the case of dry soil, if your plant does not recover even after proper watering then it’s possible that your soil has been depleted off of nutrients. In that case, it’s better to repot your plant into new soil.


Do *not* attempt to repot this plant as the roots are brittle at this point and will break apart!

3. Avoid Drastic Changes in Temperature

thermometer in plant

It’s not uncommon to see problems crop up in your cactus when winter rolls around. Cacti aren’t meant for the winter because it affects their surface tissue negatively and kills it slowly. If you suspect this is the case, then here is what you need to do.

Solution: place your cactus in a warmer environment immediately. The room should average around 75-80°F. Despite this, still take a look at the roots for extra measure.

Keep an eye on your cactus for the week. They black spots will hopefully lessen and go away, but if they do not, then they might have another problem.

4. Bacterial or Fungal infection

cactus turning brown from infection

If nothing is wrong with the roots, and the temperatue is fine, then it could be the moisture. This often happens when people mist their cacti or place them too close to fountains or other water sources where they get splashed.

Stop doing that.

If the pads of your cactus are not dry, this will quite literally pull up dormant fungus from the soil to settle onto the surface of the cactus stem. It also lays grounding for bacteria in the air to make a home and spread over the plant.

If you suspect that pests are also involved, head over to our post about it here

How to get rid of fungus gnats and keep your homegrown plants healthy?

Are you wondering how to get rid of fungus gnats? No need to be anxious, we have some remedies you will find beneficial.

Solution: Remove the plant away from other plants, change the soil, and invest in a good fungicide that will treat the infections within due time.

If you’re looking for a good fungicide to buy, check out here

Bonide 811 Copper 4E Fungicide 16oz (473ML)

This product works on most fungal infections for succulents

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5. Cutting Off Infected Areas

cactus being cut

Some patches of your cactus will simply not be salvageable. The priority is to stop the spread.

Solution: Grab a sharp knife and cut away rotten areas carefully. Discard those portions and keep them far away from the other plants!


Using your hands to scrape away rotten parts will not only damage the cacti tissue further, but even rub the infection deeper into your plant. Also, you might get hurt by the prickles, so it's only best to use a sharp object to do the job.

6. Reduce Fertilizer Use

plants being watered by tonic

It’s something that is paraphrased repeatedly: everything is good in moderation. This applies to fertilizers as well, especially nitrogen rich ones. Cacti will never need so much maintenance.

Solution: Cut down on fertilizers. During the winters especially, since the plants are dormant and will be disturbed.


We have discussed four ways to save your plant if you spot them going black: Avoid overwatering, underwatering, repotting, ensure they have a consistent warm temperature to grow in, invest in fungicide, and cut away rotten bits. We hope these help you out and that your plant spend the rest of it days in a healthy environment.

Kelly Adams Picture

By Kelly Adams

Easy Succulents Founder

My name is Kelly and I'm the the founder of Easy Succulents! I'm fascinated by this wonderful plants and I want to share with the world everything I know about them!

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Kelly Adams Picture

Kelly Adams

Easy Succulents Founder

My name is Kelly and I'm the the founder of Easy Succulents! I'm fascinated by this wonderful plants and I want to share with the world everything I know about them!



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