Cacti are succulent plants that come in a multitude of shapes and sizes. They make great house plants because they are low-maintenance and very easy to care for. They are drought-tolerant and can also tolerate certain levels of cold exposure.
However, cacti also suffer their share of problems, some of which may cause the plant to turn white.
The most common causes of a cactus turning white are sunburn, frost damage, poor ventilation, too much fertilizer, incorrect watering, chemical exposure, and pests.
In this article, we will discuss all of these causes and how to resolve each one, so if you are having this problem and wish to learn more, just keep reading.
Why is my cactus turning white?
1. Sunburn
Cacti are desert plants that can tolerate longer hours under direct sunlight than most other plants, but that does not mean they are okay with constant direct sunlight and no shade.
Too much sun exposure can cause sun damage and the cactus will start to turn white and become crisp. The sun’s ultraviolet rays basically destroy the plant’s tissue, which causes sunburn.
Too much sunlight can also cause the cactus to dehydrate as the water in the body of the plant evaporates faster than it should in the intense light and heat.
Remedy
If you think that your cactus is getting sunburn from too much sun exposure, move it to a shadier location immediately. In its new spot, the cactus should only get indirect light.
If it looks very dehydrated, spray it with water every other day to help it rehydrate.
Do not water or feed the plant while it is recovering, because this might cause more damage than good.
To prevent sun damage in the future, keep your plant in a spot where it only gets direct sunlight for a few hours a day and is in the shade for the rest of the day.
If you keep your cactus indoors, place it near a north-facing window. If the only available window in your home lets in very harsh light, you can diffuse the light by placing a sheer curtain over the window.
2. Frost damage
Another reason your cactus is turning white may be due to exposure to cold temperatures.
Cacti are desert plants that do not do well in prolonged cold conditions.
If you leave your cactus outdoors in temperatures below 50 degrees Fahrenheit, the plant may turn white, especially if ice crystals form on its skin and spines.
The damage can be temporary and easily reversible if you are able to bring the plant in from the cold quickly. However, if you leave it outdoors for days or weeks, this can lead to the plant’s death.
Remedy
If your cactus is turning white because of the cold, bring it indoors immediately and water it while letting the roots warm near a heater. You need to help the plant adjust to a warmer environment first, before treating it for frost damage.
Remove any foliage that may have died so that new growth can replace it on these areas of the plant.
Place the plant near a window that lets in bright, indirect light to help the plant recover faster from the frost damage. Make sure that you continue to water it as required and do not allow the soil in the pot to dry out completely.
Avoid frost damage in the future by placing the plant indoors or in a greenhouse that keeps it protected from the snow and the cold air.
If the cactus is in the ground in your outdoor garden, protect it by placing mulch, leaves or straw bales around the plant and its roots. You can also wrap the plant in burlap or another protective sheet that will shield it from the elements and prevent it from drying out.
3. Poor ventilation
If you place the cactus in an area with poor air circulation, this can cause it to turn white with mold.
Good air circulation helps maintain a perfect humidity level around the plant. If there is poor circulation, humidity levels will increase and encourage mold growth on the plant.
Mold will damage the cactus and cause it to rot and fall apart if not treated as soon as possible.
Remedy
If poor ventilation is what is causing your cactus to turn white, move it to a different place with better air circulation.
If the weather is pleasant and sunny, take the plant outside, or place it on the porch or patio.
If you can see some moldy spots on the plant, remove them manually.
As long as you keep the mold away, the plant will retain its normal color and will no longer be at risk of rotting.
Prevent mold growth by placing the cactus in a well-ventilated area so that there is good airflow around it.
Check the plant regularly for the presence of mold, because the earlier the mold is caught, the lower the chances of it becoming a real problem.
4. Too much fertilizer
Another possible reason your cactus is turning white is that you are giving it too much fertilizer.
Cacti do not need fertilizer often because they are not, particularly fast growers and they typically get all the nutrients they need from the potting mix in their pot.
A cactus should only be fertilized once a year, at most.
The first sign of overfeeding is yellowing leaves, while the body of the plant may turn white. The leaves may also fall off due to too many nutrients and a lack of chlorophyll.
Remedy
If you think your cactus is turning white because of too much fertilizer, you need to considerably cut the amount of fertilizer you are giving it.
Avoid overfeeding your cactus by only feeding it once a year, using fertilizer at half the strength stated on the package instructions.
If you are already using succulent or cactus mix in your plant’s pot, the cactus should not need to be fed because everything it needs is already in this mix.
5. Improper watering
Both over- and underwatering can cause your cactus to turn white. If the plant is overwatered, it will turn white and become wilted from the excess fluid in its leaves. You may also notice a slimy coating on the top layer of soil in the pot.
Overwatering can come about from giving the plant more water than it needs each time you water it, watering it more often than you need to, using a pot or soil that is poorly draining, or not adjusting your watering habits to changes in the weather or the season.
If you let a cactus remain overwatered for long periods of time, it can also lead to root rot.
This is a condition caused by prolonged exposure of the roots to waterlogged soil, which causes them to drown and die. The dead roots will be susceptible to opportunistic pathogens in the soil, which will help the rot spread even faster to the rest of the plant. Once the rot has reached the plant’s stem, the chances of recovery become very slim.
If a cactus is underwatered, on the other hand, it will shrivel and also turn white. Even though cacti can survive for long periods without water, that does not mean you can neglect to water them entirely.
Remedy
If you think your cactus is overwatered, stop watering it immediately, transfer it to a spot where it can get plenty of light, and let the soil in the pot dry out completely. Only water the plant again when the soil is dry to the touch.
If you fear that the plant has root rot, you might have to remove it from its pot to check the roots.
Gently remove the plant from the pot and wash off as much soil from the roots as you can. Be careful when handling the roots because they will be quite fragile in this state and will get damaged easily.
Inspect all of the roots closely and look for sections that have turned brown or black. These roots are rotten and will have to be removed. Use a sterile knife or pair of scissors to cut off all of the rotten sections until only healthy, white roots remain.
Lay the plant on a dry paper towel to let the roots air-dry for several hours.
Prepare a new pot, making sure it has drainage holes at the bottom, and fill it two-thirds with succulent potting mix. Place the plant in the pot and cover the roots with the rest of the soil.
Do not water the plant immediately; give it at least a week to recover from the trauma of repotting before watering it.
Place the plant in a spot where it can get lots of light to help it recover.
If you think your plant is underwatered, all you need to do is to water all of the soil in the pot until it is thoroughly soaked and excess water is flowing out through the drainage holes at the bottom.
Avoid both overwatering and underwatering by practicing correct watering habits. Check the moisture level of the soil before watering the plant, or simply feel the top two inches of soil with your fingers.
If the top two inches of soil are dry, water the plant, but if the soil is still damp, wait one or two days before checking it again.
Make sure that the pot you use for your cactus has drainage holes, and that the potting mix is also well-draining.
6. Chemical exposure
Another reason your cactus is white could be due to exposure to chemicals such as ammonia or bleach.
This can happen if you use a container to water the plant that has previously held the chemical. There may be residue in the container that you were unable to wash off and it can then make its way onto your plant, causing it to turn white.
Remedy
If you think your plant is white because of chemical exposure, you need to place it outdoors so that it can detoxify faster, because sunlight will facilitate more effective photosynthesis.
Wash the plant with warm water and mild soap, and make sure the soap is rinsed off well. This will help wash off any toxic residues from the plant’s surfaces.
Look for new growth on the plant after several weeks; this is indicative of recovery from the chemical exposure.
If, after three months, there is still no new growth, the cactus may have been so severely damaged that there is nothing you can do except dispose of the plant and start anew.
Prevent chemical exposure by keeping chemicals away from your plants and ensuring that their containers are sealed tightly at all times.
Even the fumes and vapors from certain chemicals can damage your cactus, which is why keeping them separated is important.
If you live in a small space and separating the plants from the chemicals is not an option, make sure you air the space after using chemicals before bringing the cactus back into the room.
7. Pests
Pests on your cactus can also cause it to turn white. The most common pests that create a white appearance on cacti are mealybugs, aphids, and spider mites.
These pests produce honeydew which attracts other insects and can cause the plant to rot.
The areas where the cactus has been bitten by the pests will also turn white.
Remedy
To treat a pest infestation effectively, it is always best to catch it in its early stages. To ensure this, check the cactus every time you water it and lookout for signs of pests such as yellowing foliage, white fuzz or spots, and brown or black spots.
You can use a commercially available pesticide to eradicate pests, but if you do not like using chemicals, you can also use a homemade remedy such as neem oil or a soap and water solution.
Mix two tablespoons of neem oil into a spray bottle full of water and spray the solution directly on the pests. Alternatively, mix two tablespoons of mild dish soap with water and spray this on the plant.
Make sure you keep the infested cactus far away from your other plants so that the pests do not spread. Repeat the treatment once a week until there are no more pests to be found.
Prevent infestations by making sure the cactus gets lots of sunlight because this discourages insects from flying around the plant.
Keep the plant in rooms that are not humid, so avoid the bathroom and the kitchen.
Conclusion
Cacti are popular houseplants that come in a variety of shapes and sizes, making it easy for any gardener to pick and choose species to add to their collection.
They are drought-tolerant and very low-maintenance, but that does not mean they are immune to problems altogether.
Certain problems can cause a cactus to turn white, and the most common of these are sunburn, frost damage, poor ventilation, too much fertilizer, incorrect watering, chemical exposure, and pest infestations.
The first step of any treatment, no matter the cause, is to correctly identify the problem. The faster you can determine the cause, the faster and more effectively you will be able to treat the plant.
Image: istockphoto.com / Christine Wolf Gagne