Is My Cactus Rotting or Corking?

Is My Cactus Rotting or Corking?

I freaked out last year when I noticed my barrel cactus turning brown at the base. I thought I had killed it. Turns out, I hadn’t. The plant was just getting older, doing something called corking. But here’s the thing: brown on a cactus can mean two completely different things, and knowing which one you’re dealing with makes the difference between panicking for no reason and actually saving your plant.

Let me walk you through what I’ve learned about telling these issues apart, because nobody wants to toss a healthy cactus or ignore a dying one.

Natural aging (Corking) vs. Rot

Corking is what happens when a cactus matures. The bottom part of the stem develops a brownish, woody texture that looks kind of like tree bark. It’s not pretty, but it’s completely normal. Think of it like the plant building a stronger foundation as it gets taller and heavier.

I first noticed this on my friend’s old columnar cactus. The bottom third had turned this tan-brown color, almost beige, and it felt hard to the touch. That’s corking. It usually starts at the base and works its way up slowly over years. The brown part feels firm, sometimes even harder than the green tissue above it.

Rot is the opposite. When a cactus rots, the tissue breaks down. It gets soft, mushy, and often develops a darker color, more black-brown than the lighter tan of corking. If you press on a rotting area, your finger might actually sink in a bit. Sometimes you’ll smell something off, kind of like old vegetables going bad in the back of your fridge.

Here’s how I tell them apart now. First, I touch the brown area. Corking feels firm or even woody. Rot feels soft or squishy. Second, I look at where the discoloration is happening. Corking almost always starts at the base and moves up gradually in a fairly even pattern. Rot can show up anywhere, especially where water sits or where the plant got damaged.

The color matters too. Corked areas tend to be lighter browns, tans, or greyish. Rotting tissue goes darker, sometimes with a wet sheen to it. If you see any oozing or if the brown area seems to be spreading quickly (like over days instead of months), that’s rot.

According to research from the University of Arizona Cooperative Extension, corking is a natural lignification process where the cactus deposits woody tissue for structural support. It happens in most columnar and barrel cacti as they age. You can’t stop it, and you shouldn’t try to.

One more thing that helped me: corking doesn’t spread to other plants. Rot, especially if it’s caused by bacteria or fungi, can sometimes affect nearby cacti if conditions are right. So if you have multiple plants and only one shows browning at the base that isn’t spreading to its neighbors, corking is more likely.

Squishy spots on the stem

Squishy spots freak me out more than anything else with cacti. I had a small Opuntia pad that developed a soft spot near the top, and I caught it just in time.

When you find a soft or squishy area on your cactus, that’s usually rot. It might start small, just a tiny section that feels different when you accidentally bump into it. The tissue loses its firmness. Sometimes the skin looks fine at first, but underneath, things are breaking down.

These spots can happen for a few reasons. Overwatering is the big one. Cacti store water in their stems, and if the soil stays wet too long, the roots can’t breathe. Then fungal or bacterial pathogens move in and start decomposing the tissue. I learned this the hard way with a cactus I kept in a pot without drainage holes. Terrible idea.

Physical damage also opens the door for rot. If your cat knocks over your cactus (mine did this once), or if you accidentally stab it with something, that wound can let in pathogens, especially if the environment is humid or if you water before the injury heals.

Cold damage looks similar. If your cactus gets too cold, the cells inside can burst. Then the tissue turns to mush. This happened to a cactus I left too close to a cold window in winter. The side facing the window went soft and dark.

When you spot a squishy area, you need to act fast. Rot spreads. I use a clean, sharp knife (I sterilize it with rubbing alcohol first) and cut away all the soft tissue. You have to go past the damaged part until you hit firm, healthy tissue. It feels drastic, but it works.

After cutting, I let the wound dry out completely. This can take a week or more depending on the size of the cut. I put the cactus in a dry spot with good airflow and don’t water it at all during this time. Some people dust the wound with cinnamon or sulfur powder, which might help prevent new infections. The University of California Agriculture and Natural Resources mentions that allowing cuts to callus over is critical for preventing further decay.

If the rot has spread into the base of the cactus, the situation gets trickier, which I’ll cover more in the last section. But for isolated squishy spots higher up on the stem, cutting out the damage usually saves the plant.

The other thing I check: is the soil staying too wet? I stick my finger down into the pot. If it’s damp days after watering, the mix is probably too heavy or the pot doesn’t drain well. I’ve had to repot cacti into grittier soil (lots of perlite and coarse sand) to fix this problem.

Above: A close up look at the symptoms.

Why the cactus is shrinking

My Mammillaria started looking thinner last winter, and I panicked thinking it was dying. It wasn’t. It was just thirsty and a little cold.

Cacti shrink for a pretty straightforward reason: they’re using up their stored water faster than they’re taking it in. The accordion-like ribs or the plump pads deflate a bit. This isn’t always a crisis. During their dormant period in winter, many cacti naturally slim down because they’re not actively growing and you’re watering less.

But if your cactus is shrinking during the growing season, or if it’s shriveling dramatically, something’s wrong. The most common cause is underwatering. I know we all hear “don’t overwater cacti,” but you still have to water them. During spring and summer, when they’re actively growing, mine get a thorough soak every week or two, depending on how fast the soil dries out.

Another cause is root problems. If the roots are damaged or rotted, the plant can’t take up water even if the soil is moist. I discovered this with a cactus that kept shriveling no matter how much I watered. When I finally unpotted it, half the roots were brown mush. I had to cut away the dead roots, let the plant dry out for a few days, and repot it in fresh, dry soil.

Pests can also cause shrinking. Mealybugs and scale insects suck sap from the cactus, literally draining its resources. If your shrinking cactus has white cottony spots or small brown bumps stuck to it, you’ve got pests.

Temperature stress makes cacti shrivel too. If it’s too cold, the plant goes into survival mode and pulls moisture away from the outer tissues. I try to keep mine above 50 degrees Fahrenheit in winter, though some species tolerate cooler temps.

To fix a shrinking cactus, I first check the soil moisture. If it’s bone dry and has been for weeks, I give it a good watering. I water until it runs out the drainage holes, then let it dry out completely before watering again. If the soil is wet but the cactus is still shrinking, I suspect root rot and check the roots.

According to the folks at Iowa State University Extension, cacti need a dormant period with cooler temperatures and less water in winter, but they still need some water. Completely withholding water for months can stress the plant.

If the roots look okay and watering doesn’t help, I check for pests with a magnifying glass. Those tiny bugs can hide in the spines or in the crevices between tubercles.

One last thing: sometimes a cactus shrinks right before it plumps back up and grows. If the shrinking is mild and the plant otherwise looks healthy (good color, firm tissue), I just keep up with normal care and wait.

Treating scale on cactus pads

I hate scale insects. They look like little brown or tan bumps glued to the cactus, and they’re actually insects hiding under a waxy shell. I found them on an Opuntia pad I got from a cutting swap, and they spread to another cactus before I realized what was happening.

Scale insects don’t move much once they settle in. They just sit there, stabbing their mouthparts into the plant and sucking out sap. A few won’t kill a cactus, but a heavy infestation will weaken it, cause yellowing, and make the pads shrink or wrinkle.

The first time I tried to treat scale, I just tried to wipe them off. That didn’t work. The waxy coating protects them from a lot of treatments. You have to be more aggressive.

What worked for me: I used a cotton swab dipped in rubbing alcohol and dabbed each scale insect individually. The alcohol dissolves their protective coating and kills them. It’s tedious if you have a lot of them, but it works. I did this every few days for a couple of weeks because new scales kept appearing (they have a life cycle with different stages).

For larger infestations, insecticidal soap can help. I sprayed the whole plant, making sure to get into all the crevices. The soap smothers the insects. You have to repeat this every five to seven days to catch the newly hatched ones before they develop their hard shells.

Neem oil is another option. I’ve used it as a spray, mixing it according to the bottle instructions. It works both as a contact killer and as something that disrupts the insects’ life cycle. But neem oil can be harsh on some cacti in full sun, so I usually treat plants in the evening or move them to shade for a day after spraying.

The University of Maryland Extension notes that horticultural oils can be effective against scale because they smother the insects. You need good coverage and repeat applications.

I also isolate any cactus with scale. These bugs can spread, and I don’t want them on my whole collection. The infested plant stays away from the others until I haven’t seen a live scale in at least a month.

Prevention helps too. I inspect any new plant carefully before bringing it near my others. I also try to keep my cacti healthy overall because stressed plants seem more susceptible to pests. That means proper light, appropriate watering, and decent airflow.

If a pad is absolutely covered in scale and looking rough, sometimes it’s easier to just remove that pad. I cut it off at the joint, dispose of it (not in the compost), and focus on keeping the rest of the plant clean.

Above: The tools you need to fix this.

Saving a rotting cactus

This is the scary one. When rot gets into the base of a cactus, you have to act fast or the whole plant dies.

I’ve saved two cacti from base rot, and both times involved cutting. If the rot is in the roots or the bottom of the stem, you need to remove all the affected tissue. That means cutting the cactus above the rot line.

Here’s what I do: I use a sterilized knife and cut straight through the stem, at least an inch above the highest point where I can see or feel any soft or discolored tissue. Better to take off more than you think you need. If you leave any rotted tissue, it just keeps spreading.

The cut surface needs to dry and form a callus before you can try to root it again. I leave the cut piece in a dry, shaded spot with good air circulation. This takes at least a week, sometimes two or three weeks for a thick stem. You’ll know it’s ready when the cut end looks and feels dry and maybe slightly sunken.

Once it’s calloused, I can try to root it. For columnar cacti, I just stick the calloused end into dry cactus soil and wait. I don’t water for at least a week or two. When I do water, I only give a little bit at first. The plant needs to grow new roots before it can handle regular watering.

For barrel cacti or anything without a narrow base, rooting is harder. Sometimes I’ll actually lay the cut piece on its side on dry soil until roots start forming, then gradually prop it upright.

Not every cactus survives this process. I’ve lost some despite my best efforts. But it’s the only option once rot has taken hold at the base.

The other part of saving a rotting cactus is fixing whatever caused the rot in the first place. Usually it’s overwatering or poor drainage. I check the pot (does it have drainage holes?), the soil (is it too heavy and staying wet?), and my watering schedule (am I watering too often or during dormancy?).

Research from the New Mexico State University Cooperative Extension emphasizes that cacti need well-draining soil and pots with drainage holes. They also need a dry period between waterings where the soil dries out completely.

If cold damage caused the rot, I move the plant somewhere warmer. If it was a wound that got infected, I’m more careful about protecting the plant from damage and letting injuries dry before watering.

The hardest part of dealing with rot is accepting that sometimes you just can’t save the plant. If the rot has spread throughout the stem, or if the cactus is too small to cut and re-root, there’s nothing you can do. I’ve had to throw away cacti, and it’s disappointing every time.

But more often than not, if you catch rot early and act decisively, you can save at least part of the plant. That cut stem can become a whole new cactus over time.

I keep a closer eye on my plants now. I check them when I water, looking for soft spots, discoloration, or anything that seems off. Catching problems early makes all the difference. And I’ve learned to tell the difference between normal aging and actual trouble, which has saved me a lot of unnecessary panic.

References

University of Arizona Cooperative Extension. “Growing Cacti and Succulents.” College of Agriculture and Life Sciences.

University of California Agriculture and Natural Resources. “Pest Notes: Cacti and Succulents.” Statewide Integrated Pest Management Program.

Iowa State University Extension and Outreach. “Caring for Cacti and Succulents Indoors.” Horticulture and Home Pest News.

University of Maryland Extension. “Scale Insects.” Home and Garden Information Center.

New Mexico State University Cooperative Extension Service. “Cactus, Agave, Yucca and Ocotillo Species.” Guide H-163.