Why Does My Cactus Have Brown Spots

Houseplants like cacti are the best way to enhance your interior décor with greens. These plants breathe life into the space, adding a calm vibe and boosting air quality. But maintenance of these plants is equally crucial.

Cactus may be low-maintenance, but it needs care and attention. So, if you’re wondering why my cactus has brown spots, this post is a good read.

California or Texas, regardless of where you live, your cactus can develop brown spots. Moreover, the reasons for these brown spots on the cactus can also vary greatly. Let’s take a look at the most common reasons for brown spots on cacti:

Root Rot

Brown spots on the bottom of the cactus that spread gradually are linked to root rot. It is a common issue that occurs because of many reasons. These include the following:

  • Overwatering
  • The soil is not draining properly
  • Insufficient light

It is challenging to save a cactus with root rot. It is because the plant begins to rot from the inside, making its way out. Hence, the signs of root rot appear once the problem has advanced. But don’t worry; you always have a chance.

Here it is essential to understand that sometimes corking can also cause brown spots. Corking is the cactus natural aging process. It requires no treatment. So, if you notice brown spots with thickened tissue, it is nothing to worry about. It means your plant is aging. It’s natural.

However, when the area on the cactus with brown spot is also mushy and soft, that’s root rot. The best way to deal with it is to stop watering it. Next, repot the plant with well-draining soil. Here’s what you should do:

  • Take a sharp and sterilized knife or set of sheers  
  • Cut off healthy plant stems (ensure they don’t have any signs of rot)
  • Let it dry and callous over
  • Replant it

Fungi

Another reason for brown spots on your cactus could be fungi. Your houseplant can develop a fungal disease because of two factors:

  • Highly humid conditions
  • Wet soil

Test the cactus brown patch to determine if it is fungus or rot. If the patch feels hard, it means it is a fungal infection. The best way to address the problem is to use a fungicide. It can prevent the brown spots from worsening over time. However, they will remain on the plant as scars.

Furthermore, Phyllostica is a fungus that looks like small brown discoloration spots. It most often affects the Opuntia species (pear cacti). However, if left unaddressed, the problem can spread to other parts of the plant and even to the other plants nearby.

Unfortunately, the only way to deal with the fungus Phyllostica is to cut off the healthy pads that are not affected. Dry them and then replant them in a healthy and rich soil mix. If the fungus spreads to the entire cactus plant, you must dispose of it.

Pests

Your indoor cactus houseplant may have brown spots because of pests. The same pests may infest cacti at home as their outdoor counterparts. But some problems may be unique to indoor plants because of the environmental and conditions differences. Here’s a quick overview of potential pest-related problems that can result in brown spots on your cactus at home:

Spider Mites

The brown spots right at the top are a surefire sign of mite infestation on your cactus. It is also where new growth appears. These are typically red spider mites. These insects are very tiny, and they suck the juice from the tender areas of the plant.

As they are so small, you can’t easily see them. But a good way to identify an infestation is the presence of webs and rusty brown patches.

You must act fast before the mites kill the cactus by feeding on its outer tissue layer. To rid of these mites, water your cactus from the overhead with a powerful stream of water. Additionally, use insecticidal spray on the infested plant. Keep the plant separate until sure that the plant is healthy and pest-free.

Root Lice

Another type of pest infestation that cacti are at risk of is root lice. This infestation can also cause brown spots. These pests are very dangerous because they jump from one plant to another. They can infest your entire greenhouse. Hence, it can be tough to control the infestation if you don’t take action immediately.

To control root lice infestation, follow these steps:

  • Separate new plants from the infested one
  • Quarantine the infested plant
  • Avoid sharing or recycling soil

Scales

Sometimes the brown spots that appear on the cactus may be scales. These are tiny brown insects with shells that are shaped like domes. Scales cling to the cactus and feed on the plant’s sap. Over time, scales make the plant surface completely crusted. Furthermore, when the cactus becomes highly infested, it weakens and dies.

To control scales and revitalize your cactus, spray the area affected with ethanol and water-based solution. For this:

  • Mix alcohol and water in a spray bottle in a 1:1 ratio.
  • Next, add a little bit of dish soap to the solution.
  • Now spray it on the cactus.
  • Wait 10 to 15 minutes to rub off the dead scales from the cactus.

Another way to treat it is to rub the plant with cotton swabs dipped in horticultural oil. The oil cuts off the oxygen supply to the scales and kills them easily.

Sun Damage

Brown spots on your cactus are a sign of sunburn or sun damage. Even though cacti are desert plants, not all species can thrive in the sun. Some cacti species, such as Schlumbergera cacti and Rhipsalis cacti, need partial shade and minimal light to grow and stay healthy. Exposure to too much sunlight for these species can damage them, resulting in brown spots on the top.

An alarming sign of sun damage is whitish discoloration on the side of the plant that faces the sun. If you notice it, you can save the plant by placing it in a shady area. It increases the sun-damaged plant’s chances of recovery.

However, if you overlook the whitish discoloration, these spots will eventually turn brown spots/scars. Though you can save the plant by changing its place, the brown burns will likely result in permanent damage.

Frost Damage

Like the sun, too much cold and high humidity can cause rust-like spots on your cactus. Ideally, 40 or 45°F is ideal for indoor cacti species. Similarly, a humidity level of 30 percent or below is perfect. However, going higher than these temperatures can be dangerous for the growth and survival of your cactus plant at home.

The cells of the cactus rapture when subjected to frost or excessively cold temperatures. You may not notice it immediately, but the appearance of brown spots and calluses are signs of frost damage. The cactus creates calluses on its damaged tissue to promote self-healing.

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Final Thoughts

Cacti species are excellent for enhancing your indoor space with plants and greenery. It purifies the air and breathes new life into your room instantly. However, like any other living thing, the cactus needs care.

Therefore, become familiar with the best ways to take care of your cactus, like proper light, temperature, pest control, and water requirements, to prevent brown spots and further damage. Proper care can make all the difference. Good Luck!