A clump-forming herbaceous perennial, certain varieties of garden phlox (Phlox paniculata) have been cultivated to be mildew-free. One example is Jeana garden phlox. "The individual flowers are smaller than most other garden phlox, but that does not deter butterflies from feeding on its nectar," says Sorensen. This variety is highly coveted for its ecological value and is native to the eastern United States.

Zones: 3 to 8
Size: 5 feet tall x 4 feet wide
Growing conditions: full sun to part shade; average, well-drained soil