Cactus troubleshooting usually comes down to a few main issues. Some reasons why your cactus is turning brown include too much light, too much water, pests, disease, or even a mature, healthy cactus.
As you can see, there’s no simple answer to identify why your cactus is getting brown spots, so let’s explore the potential reasons and how you can fix your brown cactus.
This post contains affiliate links, which means I may make a small commission if you click through and make a purchase.
Too Much Water Causing Cactus to Turn Brown
One of the biggest issues people have with owning indoor cacti is giving it too much water. If you’re ever unsure if it needs water or not, always err on the side of not watering it.
Your cactus will thrive much better being under-watered than over-watered.
A cactus is unlike most other houseplants. It will continue to drink the water that it’s given – coming from the desert, every drop of water is important to soak up.
Essentially, the more you water your cactus, the more it will drink and eventually start to rot.
Choosing the best type of pot (ideally terracotta or clay) will really help you avoid excess moisture.
If you’re just starting to notice your cactus going brown, you should be able to revive it by letting it dry out completely before giving it more water.
Don’t be fooled by the top of the soil – it could still be very wet or damp at the bottom of the pot.
A simple test is to pick up the pot. If it’s light and airy and feels like all you’re holding is the weight of the pot and the plant, that’s a good sign that the soil has dried out.
Another thing you can do to avoid overwatering your cactus to make sure it’s in a proper-sized pot.
You don’t want the pot to be too big, as this will just create an environment with more soil to hold more water. Place your cactus in a pot slightly bigger than its root ball.
Not Enough Light
Before your cactus turns brown, one of the first signs that it’s not receiving enough light is when the new growth is long, leggy and reaching toward the light source.
So be sure to watch for this symptom to catch it early and before it’s too late.
If you think you’re providing adequate light to your cactus, check its position in the pot.
If the soil and cactus is sitting too low in the pot (several inches down), it could be too far down to receive enough light – even if it’s been sitting near a sunny window.
Air circulation will also be limited in this situation.
This can slowly occur over time as the soil compacts and compresses, so try repotting your plant with extra soil to bring it closer to the top of the pot, about a quarter inch below the top of the pot.
Too Much Light
Believe it or not, your cactus can receive too much light, especially if it’s in front of a hot window.
If your cactus is developing brown spots on its tips, this could be a sign of sunburn.
These spots may look dark yellow, brown, rust-colored or dark orange or red.
This is a sign that your cactus is sun-stressed and can be easily fixed by moving it to an area that doesn’t produce as much direct sunlight.
If you’ve noticed brown spots on your cactus, it could be a sign of root rot.
Check to see if the brown spot and the area surrounding it is soft and mushy. If so, this is likely because your cactus has started to rot from the inside and is now showing signs on the outside.
The best way to fix your cactus after discovering soft brown spots is to slice off healthy stems (with no sign of rot) and start a new plant.
Take a very sharp set of sheers or a razor blade and sterilize it before cutting. Cut the cactus above where the rot is present, and let it dry out, callous over and then replant it.
Use new soil, and if you’re using the same pot, clean and dry it thoroughly. Unfortunately, once your cactus has started to rot, there is not much you can do to save the plant as is.
In short, if your cactus has turned brown from rot, the only way to revive it is to remove the healthy stems (parts of the plant without rot) and repot them in new soil.
Dispose of the rotted section.
Fungus, Disease or Pests
If you have brown spots or patches on your cactus, they could also be a sign of fungus, disease or pests (or all three).
Test the brown patch. If it’s still relatively hard and feels like the rest of the healthy part of the cactus, this could be indicative of fungus and not rot.
The good news is that you can save your browning cactus from dying at this point.
A fungicide should stop the ugly patches from getting worse, but unfortunately the brown spots are there to stay and will remain as scars.
A scale infestation is also a likely cause of hard brown spots on your columnar cactus.
Scale insects suck the juices from your cactus (or succulent) and cause hard, brown spots.
If you can’t peel off the scale, dip a q-tip in 70% isopropyl alcohol to drown them first, then you should be able to gently scrape it away.
If your brown spots look more like lesions or appear to be forming small holes, this could also be due to fungus from cool and wet conditions.
These spots won’t kill your cactus, but the spots won’t go away. Keep an eye on them to make sure they don’t get worse.
If the brown spots on your cactus are accompanied by small, white bumps, this is likely a sign of mealybug infestation and you need to get rid of them as soon as possible.
There are a few effective ways you can get rid of mealybugs.
Spider mites are another issue that can cause a caucus to turn brown.
If the brown spots are accompanied by thin webbing, you’ve got a spider mite problem. Get rid of these pests by spraying them with a mix of half water and half isopropyl alcohol.
Cactus Corking from Age
If your cactus is turning brown near the base of the plant or stems, this could also be that it’s starting to ‘cork’.
This is a natural occurrence in a mature plant. If the brown area in question looks almost fibrous or woody, this is simply an aging cactus and is nothing to worry about.
Cactus corking happens in mature plants to create stronger stems to better support the growing plant.
Final Thoughts on Treating a Cactus That’s Turning Brown
As you can see, there are a few reasons that can cause your cactus to turn brown.
It’s important to identify the other signs and symptoms that accompany your brown spots to ensure you’re giving it the correct treatment.
Don’t just try everything and everything, as the incorrect remedy could cause unnecessary stress to your plant and make it worse.
But with the right care and a little extra love, you can bring your dying cactus back to life after determining the cause of its browning and discoloration.