A clump-forming habit with light to dark blue spires set against light green foliage. Infrequently, flowers are white. Each individual spike of flowers opens from bottom to top and stays in bloom for several weeks. L. siphilitica blooms at the same time as L. cardinalis and attracts similar insects. Attracts butterflies. Special value to native bees and supports beneficial insects.
Blue cardinal flower prefers moist, organically rich soil in shady to sunny areas. It tolerates periods of drought better than L. cardinalis. It can tolerate deep shade in drier conditions or full sun and consistently moist conditions. Although individual plants are short-lived, L. siphilitica will maintain its presence in a garden in optimum conditions by self-seeding. Seeds need light to germinate, so be sure not to cover the growing area with heavy mulch. Do not cut plants back in the fall. May be deadheaded to encourage rebloom, but make sure to leave some seedheads for self-seeding. May be pinched back in early summer if shorter, bushier plants are desired.
Height: 2-3 ft.
Spread: 1-1.5 ft.
Bloom time: July to September
Sun: full sun to part shade
Water: medium to wet
According to Rutgers University, Lobelia are “seldom severely damaged” by deer.
photo credit: Agnieszka Kwiecień, Nova