Q: There are irregular shaped, granular deposits on front and back and upper stems of my miniature hibiscus leaves, grown in a sun room. They feel like fine sand. What is it and how to control?

A: UGA’s tropical plant expert Bodie Pennisi says it’s most likely a physiological problem called oedema. It occurs quite frequently on geraniums, sweet potato vine and even on poinsettias. The culprit is fluctuations in the environment; it is most commonly a greenhouse problem. High humidity is a primary cause.

Start checking the soil with your finger before watering. If it is damp, there is no need to add water. The deposits can be brushed off the leaves.