Why are my Geraniums's leaves cupping?

Question

The leaves are all curling upward, but the plant looks okay otherwise. What causes this "cupping"? Is it because of a magnesium or calcium deficiency?

Answer 1

Cupping of leaves is not a good sign on geraniums.  It is the prime sign of a rare disease, caused by the beet curly top virus, which is probably the most destructive and distinctive virus disease of geraniums. The normaly flat leaves become curved, and the lower and older leaves may become yellowish between the veins. Later, the entire plant becomes yellowish.  Symptoms of leaf cupping appear in autumn and again in spring. Beet curly top virus is transmitted by grafting and by the feeding of insects.  I guess you can just wait and see what happens, but in all likelyhood the health of these plants will go downhill.

Below is a great website on geraniums diseases.

Answer 2

Might be some sort of mildew.