Petunia

Petunia x hybrida is the garden petunia, a group of hybrids raised from South American species and grown almost everywhere as a summer annual. Sticky, softly hairy leaves clothe spreading or trailing stems six to eighteen inches high, and funnel-shaped flowers in nearly every colour but true blue open continuously from planting until the first frost.

Choose by flower size rather than colour. The largest double grandifloras collapse into brown mush after a summer storm and take a fortnight to recover, while small-flowered multiflora, milliflora and spreading types shed rain and keep going. In a wet summer climate that single choice matters more than anything else on the label.