Cactus Problems: Why Is My Cactus Going Soft


By: Bonnie L. Grant, Certified Urban Agriculturist

Cacti are remarkably durable and low in maintenance. The succulents need little more than sun, well drained soil and rare moisture. The pests and problems common to the plant group are minimal and usually easy to surmount. Cactus problems may range from sucking pests, like whitefly, to common rots from bacteria or fungal disease. One of the telltale signs of a problem is a soft, mushy cactus.

Why is My Cactus Going Soft?

The arid gardener may ask, “Why is my cactus going soft?” Likely causes are disease, cultivation and improper site and ambient conditions.

Cacti generally have low moisture needs. They thrive in temperatures above 70 to 75 F. (21-24 C.) in sunny locations and require little supplemental nutrients. Potted plants need good drainage holes and a soil mix with plenty of grit. In-ground plants have similar requirements.

As with any plant, cacti can become diseased or damaged. A common problem is soft spots in the flesh of the plant. These may be discolored or corky around the spot and the center is mushy and wet. The reasons for such spots may be disease or simply mechanical injury to the pads and stems of the cacti. Cactus rot issues must be dealt with quickly to prevent spread to the rest of the plant and serious loss of vigor, which may become permanent.

Cactus Problems with Fungal and Bacterial Diseases

Bacteria and fungus are introduced to the plant from openings in the flesh. The open areas may be from insect or animal activity, damage from inanimate objects or heavy weather, such as hail. The action of injury isn’t important, but the damage from fungal spores or bacteria is crucial.

Warm, moist conditions accelerate the production of fungi spores and increase bacterial production. Once the organism takes hold in your plant, you will see soft, mushy cactus. Symptoms to watch for include small sunken spots, discolored scabs, round soft areas surrounded by fruiting bodies, and black or other colored dots on the surface of the cacti skin. You may even notice some oozing of your cactus plants.

Treating Cactus Rot Issues

Cactus problems that have gotten into the root usually result in a slowly dying plant, while topical issues in the upper body can be treated easily. Most cacti respond well to excising the diseased tissue. Use a sharp sterile knife to dig out the damaged flesh and allow the hole to dry out. Don’t water overhead as the wound closes.

If the damage has infected the roots, there is very little you can do. You can try to repot the plant, removing diseased soil and replacing it with sterile soil. You should wash the roots off well before replanting in fresh potting medium.

A soft, mushy cactus can also be saved by taking cuttings and letting them root for a fresh new plant. Allow the cutting to callus over for a few days before you insert it into sand. Rooting the cutting may take several weeks. This method of propagation will produce a healthy cactus that is the same as the parent plant.

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Recently, some of my cacti have turned yellow. This never happened to me before and I’ve had good luck with most of my cacti. So I quickly did some investigating and found out why they turned yellow and what I could do about it.


Why is My Cactus Going Soft?

Cacti are remarkably durable and low in maintenance. They need little more than sunlight, well-drained soil, and rare moisture. The pests and problems common to the plant group are minimal and usually easy to surmount. Cactus problems may range from sucking pests like whitefly to common rots from bacteria or fungal disease. One of the telltale signs of a problem is a soft, mushy cactus.

The arid gardener may ask, "Why is my cactus going soft?" Likely causes are disease, cultivation, and improper site and ambient conditions.

Cacti generally have low moisture needs. They thrive in temperatures between 70 and 75 °F (21 and 24 °C) in sunny locations and require little supplemental nutrients. Potted plants need drainage holes and a soil mix with plenty of grit. In-ground plants have similar requirements.

As with any plant, cacti can become diseased or damaged. A common problem is soft spots in the flesh of the plant. These may be discolored or corky around the spot, and the center is mushy and wet. The reasons for such spots may be disease or simply mechanical injury to the pads and stems of the cacti. Cactus rot issues must be dealt with quickly to prevent spread to the rest of the plant and serious loss of vigor, which may become permanent.

Problems with Fungal and Bacterial Diseases

Bacteria and fungus are introduced to the plant from openings in the flesh. The open areas may be from insect or animal activity, damage from inanimate objects, or heavy weather, such as hail. The action of injury is not important, but the damage from fungal spores or bacteria is crucial.

Warm, moist conditions accelerate the production of fungi spores and increase bacterial production. Once the organism takes hold in your plant, you will see soft, mushy cactus. Symptoms to watch for include small sunken spots, discolored scabs, round soft areas surrounded by fruiting bodies, and black or other colored dots on the surface of the cacti skin. You may even notice some oozing of your cacti.

Treating

Cactus problems that have gotten into the root usually result in a slowly dying plant, while topical issues in the upper body can be treated easily. Most cacti respond well to excising the diseased tissue. Use a sharp, sterile knife to dig out the damaged flesh and allow the hole to dry out. Do not water overhead as the wound closes.

If the damage has infected the roots, there is very little you can do. You can try to repot the plant, removing diseased soil and replacing it with sterile soil. You should wash the roots off well before replanting in fresh potting medium.

A soft, mushy cactus can also be saved by taking cuttings and letting them root for a fresh new plant. Allow the cutting to callus over for a few days before you insert it into the sand. Rooting the cutting may take several weeks. This method of propagation will produce a healthy cactus that is the same as the parent plant.

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How to Save a Rotting Cactus

Rot is, unfortunately, a common problem on cactus. While environmental factors are involved (rot is most common when the plant is overwatered, growing under conditions of high atmospheric humidity, when the stem has been wounded, after an insect infestation, etc.), it’s important to understand that the rot itself is a fungal or bacterial disease and will likely continue to develop unless something is done.

Rot can occur on any part of the plant, from the roots to the tip, although crown rot—rot starting where the stem meets the soil—is perhaps the most common. Look for soggy black or brown, somewhat sunken tissue, often with pale green or yellow growth around it. Root rot is the most difficult to detect, since it is underground. Often the first sign of it is when the entire top of the plant begins to yellow and sag.

This isn’t rot, just the natural corky growth that appears on many older cactus. Photo: los-plantalones.tumblr.com

Many cactus become corky and brown at the base over time and that’s quite normal for those species. Try poking the base of the plant with a (gloved) finger. If the brown part is hard, it’s not rot. Rot will be soft.

Saving a Rotting Cactus

In the wild, cactus often seem to cure themselves, compartmentalizing around the wound with callus tissue to keep it from spreading. That’s not nearly so common indoors, under the lower light and higher humidity inevitably found there. Besides, the rotted section, even if the rot stops spreading, will forever mar your plant’s appearance. That’s why major surgery is recommended. Fortunately, you don’t need years of medical training to carry this out.

Sterile Tools

Sterilize the blade between each cut with rubbing alcohol. Photo: rwadamslaw.info

Any surgeon will tell you sterility in the operating room is vital. So it is with cactus surgery as well. Throughout the operations to follow, always keep your cutting tools (knife, pruning shears, even saw [for really thick stems]) sterile by wiping them down with rubbing alcohol before cutting and between each cut.

With its rotting tip removed down to healthy growth, this cactus will be able to sprout a new top. Photo: Green Lady, http://www.youtube.com

When rot occurs aboveground, near the tip or in the middle of the stem, simply cut off and toss the top part using a sharp knife or pruning shears. Study the wound on the lower part of the stem to be sure there is no sign of rot (dark, spreading tissue or even just an orange discoloration). If there is, recut even lower until you see the remaining tissue is healthy.

You may want to treat the wound with powdered sulfur, although this is not as vital as with root or crown rot.

New growth appearing from a decapitated cactus. Photo: http://www.kaktusmichel.de

Over time, the cut will callus over and one or more new stems will start to form just below the cut. It’s up to you to decide if you want to keep just one stem or more. Over time, the plant will fully recuperate … assuming, of course, you’re giving the plant the growing conditions its needs.

When the roots or the base of the stem show signs of rot, you’ll need to do more drastic surgery. You’ll need to decapitate the plant and reroot its top. This will only work if the top part is still healthy and green. If it’s already yellowing or becoming soft, might I suggest holding a little cactus funeral service … then going out to buy a new one?

Assuming the top is healthy, with a knife or pruning shears, cut off the top of the plant, above the wound. Dispose of the bottom part. If you decide to keep the pot, make sure you thoroughly empty and clean it before reuse to remove any disease spores.

If the first cut shows signs of rot, slice off another section. Photo: http://www.kuentz.com

Examine the wound. Is the tissue healthy? If you see the slightest tinge of brown or orange inside, lay the cutting on its side and slice off another section, as you would slice a carrot, then again and again if necessary, until you end up with a section showing no rot. Sometimes you’ll find the rot has spread right through the plant, in which case it’s game over, but usually you soon reach healthy tissue.

Freshly cut cactus, just before sulfur is applied. With a stem this thick, it may take months to form a good callus. Photo: thesucculentsource.com Sulfur applied to wound. Photo: I’d Tap That, http://www.youtube.com

When you’re sure you’ve excised all the rot and pre-rot (orange tissue), apply sulfur powder to the wound (it’s a natural fungicide).

Now set the cutting aside to callus over.

You may want to stand top cuttings upright as they callus over to ensure vertical growth later. Photo: http://www.shroomery.org

Callus formation can take as little as a week for thin-stemmed cactus to 3 months or more for a thick-stemmed one. You can simply lay the stem on its side if callusing will only take a few weeks. If it’s going to last a few months, the stem tip will begin to grow upward from its prone position, ruining the cutting’s future symmetry. If so, either give the prostrate stem a quarter turn each week so it won’t know which way is up or stand the cutting in an upright position.

The callus has to be hard and dry before you pot it up: if it still feels a bit soft, give it a few more weeks. Photo: http://www.zamnesia.com.

When callusing is completed and the entire cut surface is completely dry and hard, pot the cutting up into dry potting soil, using a cactus mix if that is your preference. Do not water right away! Give the new plant a few weeks in dry soil until roots start to form. Then start to water lightly. When you start to see healthy new growth, you can begin watering normally.

In clumping cactus, when rot appears on a stem, the treatment can be as easy as cutting out or pulling off the one or two stems with the disease.

You can divide clumping cactus and replant only the healthy parts. Photo: Michael Wolf, Wikimedia Commons

If it turns out to be root or crown rot affecting just one side of the plant, though, division may be the best solution. Remove the plant from its pot and pull the cluster apart, keeping only healthy stems. They’ll probably already bear roots and, if so, you can simply pot them up, although hold off on watering for a week or two.

If stems aren’t rooted, consider them cuttings. Clean them off and let them dry exposed to the air for a few weeks, then pot them up. As above, don’t water them at first, then began watering normally when you see new growth.

So, you can (often) save a rotting cactus. You just need to know how!


Stopping Cactus Rot Step by Step

Once you notice cactus rot, the first thing you need to do is prune it. If you do not remove all of the cactus rot, it will continue to spread until the cactus is dead. It spreads very fast. How you save it will depend on where it has started to rot. Cactus rot may start with some small brown spots but once you remove them, you will see that it is much worse on the inside.

  1. The first thing to do is to choose your pruning tool, which can be pruning shears or a sharp knife. If the cactus is thick, a sharp knife works best. No matter which tool you use, you want to make sure that it is very sharp so you won’t crush the stems as you prune it.
  2. Make sure that whichever pruning tool you use that it is clean and sterile before you make any cuts. This will help to prevent the spread of fungus spores and disease. All you need to do is wash your pruning tools in hot soapy water and dry before using. Some like to wash and dry them before they make each cut.
  3. In order to remove cactus rot and not kill the cactus, you need to do it in layers. This will help to make sure that you are not missing any of the rot.
  4. Continue to remove the rot layer by layer until all signs of the rot are gone. As you work your way down the cactus, the layers of rot will get thinner. Make sure that it is all gone because it can spread if any is left, no matter how small. If the cactus is an outdoor plant, make the last cut at an angle so the water will not settle on top of the wound. This can cause it to start to rot again. If it can be moved, move it to a dry area so it is protected from the rain until the cactus has had a chance to callus over.


My golden barrel cactus has pups growing on the top of it, some are quite large. After winter I noticed one of the pups was very soft around it's crown and rotting. I decided(reluctantly) to remove the pup, due to the closeness of the pups growing I removed 2 and moved the cactus under cover in case of rain. Removing the pups caused a wound on the main plant and before I knew it, a hole had formed and quite a large area is soft. Garden slaters have also gotten in there and I am unsure how much damage they have done. But there does appear to be a large area eaten away inside. The rest of the cactus has firm flesh and the other pups still attached are healthy also. Should I cut away all of the soft mushy affected flesh and expose the eaten away flesh inside, which would hopefully prevent the slaters? I realise I would have to protect the plant from rain. I am worried the insect damage will continue causing further damage if I don't do something, but don't want to lose my beautiful cactus completely. Any advice would be greatly appreciated.

Yes, I would cut out all the dead and dying parts. You also may want to replace the soil with fresh, sterile soil if you think the roots are affected.


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