Discovering unusual white spots, dots, or powdery coatings on your houseplants can be worrying at first glance. However, don’t panic just yet – not all white growths are problematic. From harmless mineral deposits to more concerning pest issues, white spots can indicate a variety of underlying causes. Read on to learn why your plant has developed white spots and how to address the problem properly.
Hard Water Deposits
One of the most common and benign causes of white spots are hard water stains. Tap water containing dissolved minerals like calcium, magnesium, and limestone can leave white crusty deposits on clay pots, in the potting mix, or around the edges of leaves when the excess water evaporates.
While these salty crusty stains are unsightly and can inhibit photosynthesis ifallowed to accumulate, they are not actually harmful to the plant. Try wiping off the deposits gently with a damp cloth or scrubbing pots and rinsing foliage if the buildup becomes excessive. Using distilled or rainwater rather than hard tap water for watering can help prevent future calcium and lime deposits.
Dry, shriveled leaves with white crispy spots and margins may be a sign of salt stress. This most often affects potted container plants that are watered with salty water. Salts can build up over time from tap water that contains high sodium, fluoride, or chloride. Fertilizers, while providing beneficial nutrients, can also leave trace salts behind.
To correct this issue, leach the soil by running copious amounts of distilled or rainwater through the drainage holes to flush excess salts out of the potting mix. Repotting into fresh soil can help reset the balance as well. Also inspect your water source and switch to non-fluoridated bottled or filtered water if needed. Keep potted plants away from cold drafts near doorways and windows in winter where deicer salts can also cause damage.
Tiny Insect Pests
Upon very close inspection, those tiny white spots may be actual living critters! Common houseplant pests that can leave white speckles, spots, and fluffy residues include:
Mealybugs are small, segmented sap-sucking insects that look like tiny tufts of white cotton on stems and leaves. They secrete a sticky honeydew substance that leads to black sooty mold growth. Remove with cotton swabs dipped in alcohol or treat with horticultural oils or insecticidal soap sprays.
These tiny flying insects look like white moths or flakes when at rest on plants. Adult whiteflies cluster on the undersides of leaves, while larvae attach themselves to leaves and look like scales. Rapid multiplication causes yellowing leaves and leaf drop. Blast away adults with water then treat with neem oil or pyrethrins.
Too small to be seen individually, spider mites cause a speckled stippling effect on leaves. Fine webbing may also be visible upon close inspection. Knock them away with a strong spray of water and release predatory mites or ladybugs to provide biological control.
Fungal or Bacterial Disease
More serious diseases that can also produce white spots include powdery mildew, downy mildew, botrytis blight, and bacterial leaf spot. Identifying the type of disease is important for proper treatment:
One of the most common fungal leaf diseases, powdery mildew is typified by white powdery spots that quickly spreads to coat the entire leaf surface. It thrives in humid conditions with poor air circulation. Improve airflow and reduce moisture. Treat with neem oil or specific antifungal products.
Also called gray mold, this fungus starts with pale green or brown spots that develop into a fuzzy white-gray mold coating. Prune out affected tissue and dispose immediately. Improve air circulation between plants.
Bacterial Leaf Spot
This is marked by yellowing leaf spots with defined margins, often with ooze or white centers. Isolate the infected plant and treat with copper-containing bactericides.
Normal Plant Structures
Sometimes white spots and markings are simply naturally occurring structures in particular plants:
Leaves with white stripes, edges, or sections are described as variegated and occur normally in certain plants like nerve plants, prayer plants, crotons, or dracaenas. This is not harmful, just a variation in pigment.
Some plants, including Ficus and Pilea, develop harmless calcium carbonate deposits called cystoliths on the undersides of leaves and stems. These create roughness that deters herbivores.
Corky white dots called lenticels are scattered across the stems and bark of woody plants to assist in gas exchange. Familiar plants with visible lenticels include birch trees, philodendrons, and pothos.
Always examine white spots closely to deduce the exact cause before taking action. While contagious pests and diseases should be addressed promptly, benign mineral deposits or natural variations can simply be left alone. With careful inspection and quick response when needed, your plant’s white spots are nothing to worry about!