Why is my moon cactus turning brown?

A colourful moon cactus is always a good investment to your cacti collection. Besides low-maintenance plant, it provides good vibes through its vibrant colours. However, it can be harmful when coloured plant starts to turn into brown. This can be a sign to take must extra care of your plant for it to thrive.

Moon cactus turning brown can be due to 1) Sunburn, 2) Corking, 3) Rot, 4) Fungal Disease, 5) Insect Infestation, and 6) Animal bites. In this condition brown spots starts to appear on parts of your plant eventually affecting the whole plant. Solution to Brown spots is by providing indirect sunlight, watering only when the soil is dry, and at last using fungicide and pesticides.


Its very depressing to see your once lovely moon cactus turn into brown, its is not a good sight. But the best part is that you can save your plant from turning brown by identifying the cause and treating it at a right time.

The 6 Reasons of Brown Spots

Moon cactus discoloration is an usual problem that many owners deal with. These brown spots are common with moon cactus. When you start to notice brown patches on your plant, take time to figure out what is wrong and then deal with it accordingly. Here are few possible causes for brown spots on your plant.

1. Sunburn

Sunburn occurs when you expose your plant to direct sunlight for an extended amount of time. In this condition, on the plant’s epidermis your plants will appear as pale discoloration, which will soon dry out and turn brown.

As we know the rootstock prefers direct sunlight, but the scion cannot withstand it. Usually, sunburn will happen on the top part of the moon cactus – that is the coloured scion. It lacks protective pigment (chlorophyll) to absorb sunlight and hence is prone to sunburn.

Sometimes, excessive sunburn may cause the outer layer of the skin to peel off. Just not Direct sunlight but using chemicals like alcohol, pesticides, and soaps during hot weather on your moon cactus will also cause burns on its epidermis.

At times, sunburn will be mistaken to corking. So if you expose your moon cactus too much sunlight and if it develops a hollow brown portion, then it will be a sunburn. Though the damage is irreversible and permanent, it does not mean your plant will not survive.

2. Corking

Corking is a natural phenomenon which usually occurs in any aging cactus. It will appear as a brown, solid, bark-like texture which will usually start from the base of the cactus and moves upwards. This brown spot appears like a laid map. Though corking is not harmful, but its appearance is unpleasant and unsightly.

Since its a natural process, the moon cactus will begin to cork or woody over time to provide a firm base as plant grows higher and starts to age. The corking begins at the bottom of the rootstock or at the union point between the rootstock and the scion.

The moon cactus are prone to break as they grows due to heavy-top. The aging moon cactus starts corking to provide support to the whole plant from breaking as a natural response. Corking is a slow process, so brown spots that are appearing overnight are not due to corking.

Identify what is causing the discoloration of the plant by touching the affected part. If it looks firm and bark kind, then your moon cactus is corking. However, if the brown part is mushy or soft to touch, it is more likely that the plant is rotting.

3. Rot

Like most of the cactus, moon cactus also do not like excess moisture on their roots. Excess water is one of the most significant causes for root rot among cacti. Brown spots are squishy indicate root rot. These spots are the dead tissues that have begun to decay.

Soil composition and pot drainage play important role in waterlogging. Excess water in the potting mix hinders air circulation for the plant’s root system and which in turn results in root rot. Rotting takes place at the roots first and then progress up to the base.

Sections of the plant may develop edema or tiny brown blisters and bumps that become permanent scars.

During the early stage of rot it is possible to save a rotting moon cactus, but it can be very challenging if the damage is severe. The brown spots are due to sunburn, corking, and edema on moon cactus.

4. Fungal Diseases

Brown spots on moon cactus can also be caused by fungal diseases. Fungi are pathogens that can infect the plants and it will be challenging to control once they have infected the plant.

Several fungi cause brown spots on the surface of the moon cactus. The infection can develop as small circular spots and gets enlarged soon after. Overwatering, high humidity, and low lighting conditions promote the growth of these diseases.

It can be very difficult to control once they have infected the host. The fungus can be detrimental if left untreated.

How To Solve Brown Spots – 4 Tips

Brown spots on a moon cactus does not mean death always. As long as you take action and act right away, you can still save your moon cactus. Here are some useful tips to solve these problems.

1. No Direct Sunlight

Moon cactus prefers bright shade and only requires 4-6 hours of indirect sunlight in a day.

The only option for severely scorched moon cactus is to move it away from the direct sun to avoid further burns. However, if you notice that your moon cactus is losing color under intense light , you can still save it.

Losing of color is an early sign that your moon cactus is gradually getting scorched. The original vibrant color turns pale. You can save your plant from the intense sunlight by transferring it to a shaded area and let it recover. Can’t guarantee that it will return to its original color, but at least, it still has its color though a little paler.

2. Water Only When Dry

Moon cactus does not like wet soil. The best way to avoid excess moisture on your moon cactus is to use the soak and dry technique.

The first thing to do is uprooting the plant if you notice an overwatered moon cactus. Check thoroughly if either the roots or the base are rotten. If the rootstock is rotten, cut off the mushy part. Then let the cut heal and replant it to a well-draining soil.

But if the rootstock is healthy, and only the roots were affected, just cut off the roots and let it for air dry for a day or two. Once completely dry, trim off the dead roots and re-pot on a bone dry and well-draining soil.

To avoid overwatering, let the potting mix to dry out between watering’s. So, here occurs a question as to how to tell if it’s dry? For this stick your finger 3-4 centimetres below the potting mix, avoiding the roots (so ideally close to the planter rim), and feel the soil if it’s wet or dry to touch.

3. Apply Fungicide

Fungi are usually very hard to remove, and fungicide are the only way to eliminate them.

Fungus infected moon cactus have high risk of dying if not treated as soon as possible. Not just that plant but other nearby plants will also be likely infected as their spores are being dispersed in the air.

To avoid this from happening, you need to act quickly upon the sight of fungus. Isolate the moon cactus right away and disinfect the spot where the plant is previously placed to prevent pathogenic organisms from spreading.

Quick solution to fungal diseases is the Chemical control. Use a curative fungicide to stop the infection and kill the pathogens. It is very crucial to read the label and use proper protection and application before using any fungicide.

For severely infected plants, it is highly recommend for proper disposal of the whole plant, including the pots.

4. Inspect and Use Insecticide

The moon cactus must be monitored regularly for insects like mites and scales as they are very minute creatures. They multiply like crazy, and you need to get rid of them right away.

Moon cactus infested with the mites and scales get weak easily as these pesky pests suck on their fluid and leave the plant dry and desiccated. In such cases, isolate your plant away from other healthy plants and remove any traces of these insects.

You can use a soft bristle brush or a pressure water spray to terminate these pests. In case of severe infestation, uprooting the plant and washing its roots will remove the insects. An effective insecticide will help completely eradicate the presence of scales and mites.

Can A Moon Cactus With Brown Spots Recover?

Recovery mainly depends on the extent of the infection or affected area. Moon cactus with too much damage can be very challenging to save, especially if the rootstock and the scion are both mushy. Saving is impossible as both of them cannot survive.

If only the rootstock is severely damaged, the scion can be saved by grafting it again to a new base. However, if the scion gets heavy brown spots, you can let go of it and keep the rootstock. If the damage is minor, the moon cactus will continue to smile. Just follow the above remedies mentioned and observe your plant if the reaction is positive.

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