Why do my marigolds have white spots all over them?

Answer by  emn2293 (101)

Chances are, your marigold has whiteflys. Take a close look and see if the plant has little tiny bugs on it. If they look like little lumps, its scale. A white powder would be powdery mildew and little cottony lumps would be mealy bugs.

Answer by  Zaka (2315)

Calcium nitrate excretions are the cause of the white spots. Water the plant a bit less and the calcium in the tap water will not accumulate on the plant's membranes.