White spots on houseplants are a common symptom among indoor plants in particular. Different problems can cause these white spots, some of them harmless and easy to fix. Quick, accurate identification of the underlying cause is crucial to know what, if anything, should be done. Fortunately, by considering the characteristics of the spots and your houseplant care habits, you can usually make an easy and confident diagnosis that points to one of the three potential causes.
Three Common Reasons for White Spots on Houseplants
- Fungal Growth: These spots are a fungus that look like a thin coating or splatter of white powder. They are one of the biggest reasons we tell people to avoid excessive misting to try to raise the humidity level. More likely, you’ll just create the perfect conditions for this powdery mildew. This is one type of fungus that can tolerate the relatively dry air in most homes, but it doesn’t like a lot of light or air circulation. If you’re seeing these white spots in your low-light areas and full-shade houseplants, it’s a good bet this is your problem. Remove the current growth with a clean cloth, or just use your fingers. Use some type of fungicidal treatment, and then look for ways to increase air circulation like setting up a small fan.
- Spider Mites, White Flies or Other Pest: Spider mites leave behind webbing designed to protect them from predators as they travel around the plant. However, many houseplant pests are also themselves white. Even common houseplant pests that are usually dark-colored, like aphids, have subtypes that are white. The white spots that are visible to the naked eye are only the full-size adults. Depending on the type of pest, the adults may or may not move. Whiteflies, as the name suggests, can fly around the plant and from plant to plant. Scale insects never move once they become adults. These insects can be removed, but some may not budge easily. You will also need to apply an insecticidal soap as well as follow-up treatments to control any eggs and larvae that may be waiting to create the next generation.
- Cold-Water Spots: The third type of white spot on houseplants is a cold-water spot. If you have a habit of using water straight from the tap, the thermal shock of cold water can destroy palisade leaf cells and leave a white callous in its place. These cold-water spots are harmless but cannot be removed without cutting out the whole leaf. Avoid using cold water in the future, and they should cease to look like blemishes after a while. You can also try a bottom watering technique for these houseplants.
* Some people also claim that the minerals from hard tap water can accumulate and appear as white spots on leaves. We do recommend using some type of filtered or purified water for your houseplants, but we also recommend ruling out these other causes before assuming it’s mineral buildup that should be treated with a diluted vinegar solution.
White Spots in Potting Soil
Aside from leaves, white spots can also show up in your soil. The most common reason for this is also mold and fungal growth from too much misting and moisture in the top levels of soil. Known as saprophytic soil fungi, these white wispy spots are easy to remove and should respond well to fungicide and better potting soil management.
Other white spots could be a buildup of salt deposits. These types of mineral deposits look a lot different than wispy fungal growth and do not depend on organic material. Thus, even more than the soil, most people first notice these spots showing up on the edge and sides of their pot.