Healthy cacti are usually bright green in color, but in some cases you may come across grafted cacti that are stained orange. But white? It’s not a natural color!
Don’t panic if your cactus slowly turns white. There can be many reasons why this problem occurs, but it’s also very easy to fix if caught early.
In this article, we will discuss some of the most common reasons why cacti turn white. Each issue manifests itself in a slightly different way, but we’ll explain them in as much detail as possible to make it easier to uncover the real culprit.
Too much water as the culprit
If you’re a little too generous with your watering can, your cactus’s distress may become apparent through the white, mushy spots on its stems. These spots show signs of root rot, where excess moisture creates a breeding ground for harmful fungi. These spots may slowly turn brown as the plant tissue dies.
Cacti are succulents and are accustomed to infrequent but heavy watering. Allow the soil to dry completely between watering to give the cactus roots a chance to recover.
Many gardeners, myself included, prefer the water bath method of watering. For this method, completely submerge the entire pot in water, making sure all the soil is under the water. When the soil absorbs all of that liquid, it bubbles. Once it stops bubbling, lift the pot to drain excess water. Repeat as necessary. I only do this once a month. This will provide your cactus with plenty of moisture while also giving it plenty of space to dry.
If you find yourself regularly overwatering, you may want to repot your cactus and start over. Choose a pot with well-draining soil and drainage holes in the bottom.
Cactus doesn’t get enough sunlight
If the color fades slowly and looks stretched, it may be due to lack of sunlight. The discolored or white appearance usually begins at the bottom of the stem and slowly continues upwards.
This can be a particular problem in early fall, when it’s always cloudy but not so late or cold that plants go dormant. As a result, the cactus needs as much sunlight as possible to function at its best.
Cacti require at least six hours of indirect sunlight each day to photosynthesize effectively. Move the pot to a sunny location. South- or west-facing windows are ideal, but if natural light is limited, consider adding grow lights. Also, don’t forget to rotate your plants around to ensure even sunlight on all sides and encourage balanced growth.
On the other hand, overexposure to sunlight is not a problem, but it rarely appears as white or pale stains. If your cactus is exposed to direct sunlight all day long, brown burnt spots will become noticeable. These stains are caused by UV rays that destroy living cells. However, the solution is the same. Move the pot to a more suitable location.
Cacti turn white due to over-fertilization or lack of nutrients.
Nutrient imbalance is one cause that manifests itself in many ways. As cacti take in more nutrients than they can absorb, they can accumulate as white, scab-like deposits on the plant and soil surfaces. This also applies to minerals present in water. Conversely, a lack of nutrients or an excess of some nutrients can cause the cactus to fade or change the color of its spots.
White spots on cacti due to excess fertilizer or lack of nutrients are the most difficult to reliably detect, at least without various test kits, and can be quite expensive.
If you think the white spots on your cactus are caused by over-fertilizing, reduce the amount of fertilizer. Cacti should only be fertilized every 8 to 10 weeks during the growing season.
Watering with tap water can lead to mineral deposits, especially if the water is hard. This usually appears as a thin layer of white dust on the surface of the plant where water evaporates.
A cactus that has turned white due to frostbite
Frostbite occurs when cacti, which are normally adapted to warm, dry climates, are exposed to greater temperature increases. The telltale signs are white or discolored spots on the surface of the cactus, often with a soft, mushy texture.
The damage caused by frostbite destroys plant cells, leading to loss of pigmentation and structural integrity.
To correct frostbite, first assess the extent of the damage. Using a clean, sharp tool, cut away the visible diseased area, leaving healthy tissue behind. My guide on how to trim a cactus the right way will help you with that.
If frostbite is widespread, consider moving your cactus to a warmer location or temporarily protecting it during cold snaps.
The reason why cacti turn white is due to pest infestation.
There are many insects and insects that announce their presence by leaving a white, waxy residue on the surface of the cactus. Some small invaders lay small eggs in clusters, creating white spots on the surface of the cactus.
A white appearance on cacti is often caused by insects such as spider mites, aphids, and mealybugs. You may notice a white, waxy residue called honeydew on the surface of the plant, or cotton-like clumps, or small shell-like protrusions on the cactus.
If left unchecked, a pest infestation can compromise the overall health of your cactus and lead to overall wilting.
Minor infestations can be resolved by simply wiping the pests with a cotton swab soaked in rubbing alcohol. For more widespread infestations, choose an insecticide and isolate the infected cactus to prevent the pest from spreading to other plants.
Before you go…
Dealing with diseased plants, such as cacti with white spots, can be a pain. Once your cactus is healthy again, you want to keep it that way for a long time. And your cactus deserves to shine, so we have things to make sure your cactus looks the best it can. Be sure to check out my guide to cleaning succulent leaves with easy recipes to make your homemade leaves shine…
Featured image by Katja Schultz
