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:

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:

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.

Stem Rot

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

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:

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.

Root or Crown Rot

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:

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:

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Sulfur applied to wound. Photo: I’d Tap That,

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:

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:

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.

Clumping Cactus

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.

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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!


Do You Need to Let Cuttings Callus Over?


You’ve taken the cutting … but now, do you need to let it form a callus before you start to root it? Source:

There seem to be two schools of thought about starting cuttings: some gardeners pot up their cuttings immediately. They cut off the stem, remove lower leaves and slip the cutting into moist potting soil without delay. Others claim better success when they take the cutting, then let it lie around for from a few hours, perhaps overnight, until a callus (layer of harder protective tissue) forms. Only then do they pot up the cutting in moist soil and allow the process of producing new roots to begin.

Who’s right?

They both are. It just depends on what type of plant you are trying to root … and on your own preferences!

Thin or Soft Stemmed Cuttings


Pot up coleus cuttings without delay: they do not like to dry out! Source:

Cuttings of plants with thin or soft stems, especially those with thin leaves (coleus, abutilons, etc.) wilt quickly when the cut end is left exposed to the air. That’s a sign of severe stress and is not good for the cutting. Pot these up immediately … and cover them with a clear plastic mini-greenhouse (dome, plastic bag, etc.) without too much delay to prevent further water loss from the leaves. (Inside a mini-greenhouse, the atmospheric humidity will be close to 100%, reducing transpiration from the cutting’s leaves to almost nothing and thus allowing them to stay turgid.)

Also, keep the substrate of these plants slightly moist at all times until they root (new growth will then appear). Drought stress is never good for them.

Succulent Cuttings


You can let succulent cuttings lie around until the cut end calluses over before potting them up. Source:

Cuttings of plants with thick or woody stems, especially those plants considered succulents, don’t lose water nearly as quickly as softer-stemmed plants. Many have thick leaves that likewise hold onto their moisture; some have no leaves at all. You can actually drop such stems in an envelope and mail them to a friend with no further thought: they’re that tough. And they tend to rot if you don’t wait for the cutting to form a callus, a hard, dry “crust” at the base of the cutting. That can take anywhere from a few hours to a few weeks, even a few months in extreme cases.

In general, the thicker the stem, the longer it takes to seal itself off. Moderately thick-stemmed cuttings like crassulas, sanseverias and echeverias are ready to pot up in just a few days, even only overnight*. Likewise with cuttings of succulent leaves (many plants in the Crassulaceae family—Crassula, Echeveria, Kalanchoe, Sedum, etc.—, as well as species of Haworthia, Gasteria and Sansevieria, among others, root readily from leaf cuttings). There is only a very small wound on a leaf cutting, the spot where it was once attached to the stem, and it heals over quickly. Just leave such cuttings lying around on a tray in a dry spot, in light or in dark, until the cut end no longer looks moist before you pot them up.

*Alternate possibility: if you don’t want to wait to let these thinner-stemmed succulents callus over, pot them up immediately … into a totally dry rooting mix. Then leave the mix dry for a week. That will give them time to callus over out of sight in the growing mix. Then start to water … moderately. They won’t need much moisture until they’ve rooted.

Note that you don’t need to cover succulent cuttings with a mini-greenhouse while they’re rooting. They prefer the lesser humidity of open air.

When Stems Are Really Thick


Some cacti and succulents have really thick stems: you should let their cuttings callus over thoroughly before you try to root them. Source:

Really thick-stemmed succulents can take ages to callus over. There are cactus and euphorbias, notably, with stems that can be 6 inches (15 cm) or more in width you’ll need to harvest with a saw and they can take weeks or months to fully callus over. They tend to be difficult to root and the chances of rot are quite high. To root these with as little loss as possible, try to take the cutting in the spring (always the best season for any cutting, with summer a close second) and do so by harvesting a secondary stem (branch), cutting where it joins the main stem: this leaves the narrowest possible wound, one that will callus over more rapidly. That said, you can cut the top of most cactus and euphorbias at their thickest point and the resulting cutting will still eventually callus over, giving you something you can tray rooting … after several months!


Euphorbia sap flows like blood when you harvest a stem. Staunch the wound on both the cutting and the mother plant by spraying with cold water. Source:

One note about euphorbias (genus Euphorbia). They produce copious amounts of white sap (latex) when you cut them. (This sap is highly irritating on most species, so wear gloves, and is also likely toxic, so don’t get it in your mouth or eyes.) To stop the “bleeding”, either dip the cutting in cold water or spray with cold water. That causes the sap to coagulate. Or expose it briefly to a candle or match flame to cauterize the wound.

Keeping Cuttings Upright


If possible, keep cuttings upright if they need several months to callus over. Source:

Typically, cuttings undergoing callusing are just left lying on their side and that’s fine … if you’ll be potting them up fairly soon, within a few weeks, for example. If the healing process is going to take months (again, mostly thick-stemmed cacti and euphorbias) and you leave them lying on their side in the same position all that time, the tip will start to grow upward—yes, even on a cutting with no roots! —, resulting in a plant with a bend in the stem when you stand it upright again for rooting. Either rotate the cutting regularly as it calluses over, giving it a quarter turn every few days, or find some way of keeping it upright while you wait for the callus to form. I’ve seen gardeners lean their cuttings against a wall, or tie them to stakes to hold them upright, but personally, I just drop them upright into a heavy drinking glass or other upright container. And wait.

Potting Up Callused Cuttings

The “quick-callusers” (i.e. most succulents with fairly narrow stems, like the typical crassulas, sanseverias and echeverias most people take cuttings of) root readily in regular potting or cactus soil. No rooting hormone is needed. One secret though: keep them distinctly on the dry side, barely watering, until you see signs of growth.

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Yes, even thick-stemmed cuttings will eventually produce roots… and become an independent plant. Source;

Thick-stemmed succulents (again, mostly cacti and euphorbias) are tougher to root and more subject to rot. I recommend applying rooting hormone before you set them in soil (it also happens to have a useful fungicidal effect)… and keeping the soil dry (i.e. don’t water at all!) until you see some growth, usually a sign rooting has started.

Also, keep all cuttings warm throughout the rooting period.

Semi-Succulent Cuttings


Pelargonium cuttings are semi-succulent. You can let them callus overnight… or not. I like to root them in sand or perlite. Source:

Some plants are in-betweeners: they’re neither true succulents nor true non-succulents. This includes the ever-popular pelargonium, aka geranium (Pelargonium), hoyas (Hoya) and a few others. You can treat these plants either way: some people pot up their semi-succulent cuttings immediately, others let them callus over for a short period, usually overnight. Both ways work.

Might I suggest rooting semi-succulents in an especially well-aerated mix, say perlite or sand? (Better aeration reduces losses due to rot.) And applying rooting hormone to the cut end? Plus keep the rooting medium only slightly moist. Semi-succulent cuttings just seem to be a bit touchy when it comes to watering and need a bit more attention than more typical cuttings.

So, whether you let cuttings callus over or not depends on the type of plant you want to reproduce … and how you garden. The choice is up to you!20180410A

When to Use a Mini-Greenhouse for Cuttings


All sorts of transparent containers can be converted into mini-greenhouses for cuttings.

Taking cuttings of houseplants is simple enough – in most cases, you just stick the cutting upright in moist potting mix and you’re off to the races! – but you’ll have more success by covering the still-fragile future plant with a mini-greenhouse of some sort. After all, cuttings don’t yet have roots and can dry out very quickly when exposed to the air, losing water to evapotranspiration. This is doubly true for cuttings with thin leaves. If you cover them with a mini-greenhouse, though, the air inside will be saturated with moisture, and therefore the cutting will no longer lose its precious water to transpiration, giving it a better chance of recovery.

You can use just about any transparent container as a mini-greenhouse: a transparent plastic bag (prop it up with coffee sticks so the bag doesn’t collapse on the plant), a wide-mouth bottle turned upside down, a clear plastic container for vegetables, fruits or pastries that you recycled, or even the bottom of a soft-drink bottle you’ve cut specially for this purpose.

Remove the greenhouse when new leaves start to appear, indicating that rooting has begun, which may take a few weeks. Your cutting is now an officially rooted plant, ready to grow on its own and greenhouse care is no longer needed.

Some Cuttings Like It Dry

If the vast majority of cuttings benefit from high atmospheric humidity while they are rooting and should therefore be placed in moist soil and covered with a mini-greenhouse, there are some cuttings that root best under drier conditions. And this is especially the case with succulents, a group that includes desert cacti, crassulas, sedums, aeoniums, and many others.


Wait until succulent cuttings callus over before potting them up. This cactus cutting, for example, might take a month to callus over.

For these plants, cut off the top of the stem, but don’t plant it right away. Let it dry for a while, until the wound callouses over, before potting it up. You can simply lay the cuttings on their side on a plate or a shelf while you’re waiting. It takes 2 to 3 days for most succulents to form a callus, but a month or more for those with very thick stems (large cactus and euphorbias, especially).

Stick the cutting upright in a pot of dry soil (not moist as you would for other plants) and don’t water right away. Wait until you see signs of growth, which can sometimes take a month. Yes, as odd as it may seem, these plants will more easily produce roots in dry soil! And of course, don’t cover them with a mini greenhouse, as this could lead to rot!

Once new growth appears, start a normal watering program and your “succulent cutting” will soon be a thriving plant!