Why Does My Cactus Have Brown Spots

What can we do to preserve the life of the cactus we adore? Some of the brown patches first appeared in December, and it is now expanding. It has always been wrapped in burlap and protected against frost with Styrofoam containers on the points. The same markings can be seen on other cacti (Mexican Fence Post) at Saddlebrooke. I would be very grateful for any assistance.

A number of factors, including excessive sun exposure on recently planted cacti, animal damage, frost, hail, some chemicals, and illnesses, can all result in brown blotches on cactus. Your cacti’s patches may be fungal lesions, which occasionally develop during periods of cool, rainy weather like this winter. The damage is typically only ornamental and won’t kill the plant, but it is also irreversible, leaving a scar. You should notice a decrease in the occurrence of this disease in your community now that summer-like weather has arrived.

How can brown patches on cacti be removed?

Look to check if the brown spot and the vicinity are mushy and soft. If so, your cactus has probably started to rot from the inside out and is now displaying symptoms on the outside.

After noticing soft brown areas, the best technique to fix your cactus is to cut off healthy stems (without any signs of rot) and start a new plant.

Before cutting, disinfect a razor blade or a pair of extremely sharp sheers. Cut the cactus above the area of rot, allow it to dry, callus over, and then plant it again.

Use fresh soil, and thoroughly clean and dry the pot if you’re using the same one. Unfortunately, there isn’t much you can do to save your cactus as is once it has begun to decay.

In other words, the only method to revive a cactus that has developed rot is to cut off the healthy stems—those portions of the plant that are still green—and repot them in fresh soil.

How are cactus spots treated?

It might be challenging to stop a fungus after it has started to infect your cactus. A fungicide application can usually help if the damage isn’t too severe. Finding some healthy, disease-free material and starting a new plant from a cutting may be the best option if the plant is covered in lesions. Cutting should be done with a sterile knife, and any potential spore adhering should be killed by sulfur dusting.

Many fungal outbreaks can be stopped by managing the cultural conditions with lots of heat, under stem irrigation, sterile potting material, and ventilation. Cutting off the diseased tissue is another approach to rescue a plant. Even though not all fungi respond to it, it occasionally works. To guarantee that every infection is eliminated, sterilize your cutting equipment once again and remove more tissue than looks to be impacted. As the area calluses, keep it dry and keep an eye out for any indications of reinfection.

Should I remove the brown cactus parts?

When a cactus begins to rot, all of the rot needs to be removed in order to salvage the plant. If it is not entirely eliminated, it will spread and finally kill your cactus. Additionally, cactus rot spreads swiftly.

You must move quickly if you don’t want to wind up with a dead cactus plant.

What needs to be done to save your cactus depends on where the decay is occurring. Therefore, I’ll start by demonstrating how to rescue a cactus that is rotting top down.

I’ll then discuss how to salvage a cactus that is rotting from the bottom up in the part that follows.

How To Save A Cactus Rotting Top Down

Cactus tip rot might give false hope. If you see a few little brown spots on a cactus, you can mistake them for minor rot.

Then, as you work to eliminate the troublesome areas, you come to the conclusion that the interior is actually much, much worse than the exterior.

So, before you begin chopping, take a moment to mentally get ready for what you might discover. Ready? Okay, follow these instructions to get rid of cactus stem rot.

Step 1: Select your pruning instrument.

To get rid of the rot, use a sharp knife or pruning shears. I advise using a sharp knife if your cactus is particularly thick.

Otherwise, precision pruners or bonsai shears would be excellent for little plants with thin stems. Just make sure they’re razor sharp to prevent crushing the cactus stem.

Clean your cutting instrument in Step 2—do not omit this step!

Before making any incisions, it is crucial that the equipment you select to use is sterile and thoroughly clean.

It will be easier to stop the spread of illness and fungus spores if you use a clean pruning instrument. You only need to clean your pruning shears or knife with soap and water before drying it off and beginning.

Additionally, I advise cleaning and drying it once more in between each cut. To disinfect it, you might also dip it in rubbing alcohol.

Step 3: Layerarily remove the cactus stem rot

To ensure that all of the rot has been eliminated, it is advisable to trim off the affected areas in stages.

You can see that my cactus plant’s middle, despite appearing to be healthy, nevertheless has interior rot. Consequently, we must continue.

Step 4: Continue stripping away layers until no rot is visible.

The rot will become thinner and thinner as you remove plant layers one by one.

But keep in mind that even a small amount of rot can spread. Therefore, until there are no longer any indications of rot on the plant, be sure to remove all indications of brown, squishy, and mushy cactus material.

Make the last cut on your cactus at an angle if it’s an outside plant to prevent water from pooling on top of the wound (which will likely just cause it to rot again).

If at all feasible, I would also relocate the plant to a dry location shielded from the elements until the wound had calloused over.

Unfortunately, before I realized that the top of my plant was going brown, the rot was already rather bad. To completely remove the cactus, I had to cut off more than half of it.

Even though it was challenging for me to cut this cactus in half, I know that if I had left any rot behind, my plant would have died within a few weeks.

Cactus Care Tips After Pruning

If you have to operate on one of your favorite plants, be sure to watch it closely afterward to make sure it doesn’t continue to decay. If it starts to decay once more, eliminate the new rot by following the same instructions as before.

The wound should callus over within a few days, and your cactus will eventually send out new growth close to the cut.

I hated having to chop my cactus in half to get rid of the rot. However, in the end, I believe it gave the plant more personality.

How To Save A Cactus Rotting Bottom Up

Unfortunately, there isn’t much you can do to salvage a cactus that is decaying from the ground up or has damaged roots.

In this situation, cutting healthy stem sections off and replanting the cuttings is the best course of action.

To ensure that all of the rot is removed from the cuttings, prune your cactus back in layers as instructed in the steps above. Till the cut end has callused over, let the cutting dry for a few days.

Wait to irrigate the soil until the cutting has new growth. Cactus cuttings can take several weeks to root, depending on the kind you have.

What does a cactus that is overwatered look like?

The obvious indicators of an overwatered cactus caused by a fungus in the soil include black or brown blotches and mushy stems. It’s time to carefully chop them off with a knife if you experience any of these bodily symptoms. Use a sterilized knife while handling a rotting plant to prevent the spread of the infection.

You will have to exert more effort if the damage is severe. Essentially, what you’ll be doing is multiplying the portions of your plant that are still alive. Wear nitrile gloves to protect your hands from the cactus’ spines while you chop off the rotting sections, and exercise extreme caution when handling the plant. After cutting out the damaged areas, let your cuttings air dry for a few days, or around a week.

How frequently do cacti need to be watered?

The most frequent reason for cacti failure is improper watering, whether it is done too much or too little. Cacti have evolved to store water for extended periods of time and can maintain moisture through droughts because they are endemic to arid regions and dry temperatures. They have a limited capacity, which is why over-watering can result in a variety of issues.

When it comes to regularity, watering your cacti will largely depend on the season but also on the variety. Checking the soil is the easiest technique to determine whether your cactus needs water: It’s time for a drink if the top inch is dry. That entails applying the “soak and dry procedure” on cactus.

What is the soak and dry method?

The soak and dry technique is thoroughly wetting the soil until part of it begins to flow out the drainage hole, then waiting until the mixture is nearly dry before wetting it once more. If done properly, this strategy will help them endure a period of under-watering should you need to travel or leave the house because it takes use of their natural tendency to store water (or if you just get busy and watering falls to the wayside, as happens to all of us now and again).

Watering during the growing season versus the inactive season

Like with many houseplants, the season affects how frequently you need water. It becomes more crucial that you get in the habit of examining the soil to determine whether your cacti are thirsty. A healthy cactus needs watering every one to two weeks during the growing season, according to general wisdom. The frequency changes to once every three to four weeks during the off-season.

Even then, it’s crucial to examine the soil. The same way that not all interior spaces and not all cacti are alike. The only way to be certain that your cactus require watering is to carefully examine the soil to determine how dry it is because there are so many different factors.

Why do the brown and black stains on my cactus exist?

Cacti and succulents commonly experience cactus black spot. If not addressed in a timely manner, it may have an impact on the plant’s health, appearance, and even survival.

Typically, fungus or bacteria that invade through wounds in the plant’s skin generate the black patches on cactus plants.

However, chemical damage from fertilizers or soil additives can also result in black blotches.

You may find out how to notice black spots on cactus plants and the best way to handle this issue by reading the information below.

Fungal Diseases

When a plant is handled with unwashed hands or carelessly pruned with shears that haven’t been sanitized after use, the fungus can enter via any wounds in the plant’s skin.

There are several different fungi that can cause black spots on cactus plants; there isn’t just one kind that does it.

The most prevalent fungi on cactus plants include Cladosporium, Ramularia, Diplodia, and Botryosphaeria species.

How to Treat Fungal Diseases on Cactus Plants

Trimming away the diseased cactus plant sections with clean scissors or a sterilized blade and discarding them in a sealed bag to prevent the spread of the infection to other plants may be adequate for lesser infestations.

For larger infestations, it is preferable to apply a fast-acting fungicide, which you may get from your neighborhood garden center.

The type of fungus generating the black spots may require a different treatment, however mixing equal parts hydrogen peroxide and water is a solid overall strategy.

Use a cotton swab or brush to apply this solution to the affected plant sections and allow it dry completely before continuing.

In order to lessen the possibility of skin damage to the plant, you can also mix one part white vinegar with two parts hydrogen peroxide.

Bacterial Diseases

Xanthomonas or Pseudomonas bacteria, depending on whether they were introduced through wounds in the plant’s epidermis or through contaminated water and soil additives, may also be the source of black spots on cactus plants.

Despite being less frequent than fungi, these bacteria are even harder to treat.

How to Treat Bacterial Diseases on Cactus Plants

The vascular system of a plant is often infected by bacteria, necessitating considerably harsher curative measures.

Using the antibiotics oxytetracycline and streptomycin in combination is the most efficient way to treat bacterial black spots on cactus plants.

You must combine one part of each antibiotic powder with five parts water, then use a spray bottle to administer this mixture to all diseased areas until they are well saturated.

Cover the entire plant, making sure to include any healthy spots where the solution might drop.

Leaf Spot Damage

Leaf spot disease, which affects the plant’s leaves, can also result in black spots on cactus plants.

These lesions are frequently brown, round, and have a black border, which makes it simple to recognize this widespread issue.

Leaf spot lesions can form anywhere on the plant, but they frequently group together and enlarge with time.

If the leaf spot disease is not treated, it gradually spreads to the cactus leaves’ veins, making them brittle and prone to falling off.

How to Treat Black Spots Caused by Leaf Spot Damage on Cactus Plants

Pruning off the impacted plant leaves and relocating the plant to a more sunny location are the best ways to treat black spots brought on by leaf spot.

It will have more exposure to sunshine, which aids in promoting healthy growth, and this will help avoid new infections.

Chemical Damage

Most often, chemical damage from fertilizers or soil additives containing metals like manganese, zinc, and iron results in black blotches on cactus plants.

However, through water runoff, pollutants may also indirectly induce black patches on cactus plants.

The chemicals may be transferred by water droplets onto the plant’s surface if the soil has been regularly watered with polluted water, such as from a pool or hot tub.

How to Treat Black Spots Caused by Chemical Damage on Cactus Plants

One part milk and two parts water that have been boiled for at least five minutes must be sprayed on the plant.

Spray this solution on all afflicted areas until they are completely saturated.

The milk helps neutralize the chemicals that have burned through the skin tissue while also providing nutrients that may help promote new growth in the affected areas.

Sun Damage

Sun damage may be the cause of black patches on cactus plants that are not brought on by fungi, bacteria, or chemical agents.

Any black area on a cactus plant, in general, signifies that the skin tissue has been damaged and should be given extra protection from sunlight for at least a year while it heals.

How to Treat Black Spots Caused by Sun Damage on Cactus Plants

As the cactus heals, keeping it out of direct sunlight is the greatest remedy for solar damage.

If at all possible, plant the cactus in a spot with indirect light. Water it sparingly, and wait until the soil is totally dry before watering it again.

How to Treat Black Spots Caused by Pest Damage on Cactus Plants

If your cactus has been affected, it will need to be confined for a few weeks while the condition is treated because pests can quickly move from plant to plant.

Use insecticidal soap to kill the pests since it includes fatty acids that damage the pests’ cell membranes.

Although insecticidal soap is effective against a variety of insects, it should never be applied to plants that are exposed to direct sunlight since it could harm the plants.

For lesser infestations, you can simply mix one tablespoon liquid dish soap with two cups of water. Until the issue is fully resolved, you must repeat this procedure every five days.


If soft, mushy regions on the plant’s epidermis and black spots appear along with them, the plant may be showing signs of rot.

Rot is typically brought on by bacterial or fungal infections, though it can also happen when cactus plants are exposed to excessive moisture.

Any bacterial or fungal infection that enters the plant’s root system and hinders it from properly absorbing water might result in root rot.

Additionally, an infection that originates at the roots and moves up through the lower regions of the cactus plant is what causes crown rot.

Unless they have already sustained damage or are infested with pests like scale insects and mealybugs that weaken plant tissue and make them more susceptible to subsequent infections, cacti are normally not particularly prone to rot.

How to Treat Black Spots Caused by Rot on Cactus Plants

Making sure that your cactus plant is not damp for extended periods of time is the best technique to treat black patches brought on by rot.

It’s crucial to let the top layer of potting mix dry out before re-watering because rot typically occurs after the soil has been kept moist.

Repotting the cactus plant in fresh potting soil that includes some sand and perlite, which aids improve drainage, is required if you suspect crown rot or root rot.

If you decide to use cactus mix, be careful not to pack it too firmly around the roots because doing so could suffocate them and make it harder for water to get to the root system.

Assist the potting mix’s drainage by adding at least two inches of sand and perlite.