Leaves going pale in hanging baskets

Hanging baskets with trailing petunia, and lobelia were planted in late May (after frosts) and were thriving initially. In last few weeks leaves have gone pale green and flowers have a faded ‘washed out’ look, but are not falling off. Baskets have been kept watered and fed with tomato feed (maybe too much?) from the start. I have been growing baskets successfully for several years and never saw this problem before.