What are the white spots on my plant?
Three unrelated things look white on a leaf, and the test is simply whether it wipes off.
The causes, and how to tell them apart
Mealybugs common
How to tell: White cottony tufts tucked into leaf joints and undersides. They wipe off and are slightly sticky. Often with sticky residue on leaves below.
What to do: Dab each one with a cotton swab dipped in 70% isopropyl alcohol, then treat with insecticidal soap weekly for four weeks — they hide in the soil and crown and come back from a single missed one.
Powdery mildew common in still air
How to tell: A dusty white coating spread flat across the leaf SURFACE, like flour. Does not wipe off cleanly.
What to do: Improve airflow, stop wetting the foliage, remove the worst leaves, and space plants further apart.
Mineral deposits from hard water harmless
How to tell: Chalky white flecks or a crust, often also on the pot rim and soil surface. Wipes off with a damp cloth.
What to do: Cosmetic only. Wipe the leaves; switch to filtered or distilled water if it bothers you.
Telling the three causes apart by plant
Two of the three causes above can be narrowed before you touch the plant. Mealybugs favour particular species, and the mineral-deposit explanation only really applies to plants that react to what is in your water in the first place.
| Species | Listed pests include mealybugs | Salt / mineral sensitive |
|---|---|---|
| Monstera | yes | yes |
| Pothos | yes | — |
| Heartleaf philodendron | yes | — |
| Aglaonema | yes | yes |
| Corn plant | yes | yes |
| Madagascar dragon tree | yes | yes |
| Snake plant | yes | yes |
| ZZ plant | yes | — |
| Money tree | yes | yes |
The physical test settles it regardless: mealybugs wipe off as a soft waxy smear and come back; mineral deposits are gritty and stay where the water sat.
Plantroster compares this month's photo against last month's, so slow changes — the ones you stop noticing because you see the plant every day — get flagged.
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General horticultural guidance, not a diagnosis of your specific plant.