What kind of medium are they growing in? It looks compost-based to me and if it is then that's likely the problem.

Rodney

Ah it is. Should I switch to a good gardening or potting soil?

That would mean pulling the plants up, which would make things worse.

The heat, also, might be a problem.

(Duplicate post deleted.)

This post was edited by grandad on Tue, Sep 16, 14 at 7:16

Agree with Rodney the growing medium could be your problem. If you don't want to re-pot the plants, you might try adding a nitrogen containing fertilizer or supplement...just be careful, adding too much nitrogen could hurt your plants. You can also sprinkle soil on top and water it in to help balance out the organic matter.

This post was edited by grandad on Tue, Sep 16, 14 at 7:10

BTW - the white blotches are natural markings. Only the dry yellowish patches betray a problem.