Blue vervain produces small, densely packed, bluish-purple flowers from early summer to early fall. Growing up to 5 feet tall, this plant is a perennial that can add structure and texture to the landscape. Blue vervain is versatile and can be planted in moist to wet rain gardens, pollinator gardens, native gardens, naturalized meadows, near ponds, near streams, on banks, and on slopes in full to partial sunlight. This species is native to the Chicago region according to Swink and Wilhelm’s Plants of the Chicago Region and current research.
Size and method of spreading:
Blue vervain matures to a height of 2 to 5 feet and a width of 1 to 2 ½ feet. The plants spread slowly by producing offsets through underground stem structures (rhizomes) and by self-seeding.
Native geographic location and habitat: (include C-value if appropriate)
The native range of blue vervain includes the entire continental United States. C Value: 4.
Attracts birds or pollinators: Blue vervain attracts a number of long- and short-tongued bees, birds, butterflies, flies, moths, skippers, and wasps.
The leaves of blue vervain are up to 6 inches long and 1 inch wide (lanceolate) with short, winged stalks (petioles). They are yellowish-green to medium-green and have prominent veins. The edges of the leaves are coarsely toothed (serrate margins) and the bases are rounded while the tips are tapered to a point. Larger leaves can have large, spreading lobes at the base.
Blue vervain flowers are tiny, bluish-purple, and densely packed onto branched stems that give the appearance of a candelabra. Only a few flowers open at a time, and they mature upward from the bottom. The flowers occur on spikes that are approximately 2 to 5 inches long and the spikes are branched (panicles). Each flower is up to one-quarter of an inch in diameter and has a tubular petallike structure (corolla) that divides into five rounded lobes at the top. Inside of the corolla tube are the four pollen-bearing structures (stamen) and an ovary (pistil). Surrounding the base of the corolla is a leaflike, green to purplish-red, tubular structure (calyx) that divides into five sharply pointed hairy lobes.
The fruit produced by blue vervain is small, brown, dry, four-parted, and does not open to release the seeds (schizocarps). The calyx from the flowers remains around the fruit as it matures (persistent calyx).
Deadheading sweet black-eyed Susan can help to promote additional blooms and reduce self-seeding. Good air circulation can help to prevent issues with powdery mildew. Taller plants may need staking for support.
List of pests, diseases, and tolerances:
Sweet black-eyed Susan is susceptible to powdery mildew. It tolerates heat, humidity, some drought, and deer once it has become established. A variety of soils can be tolerated, as long as they drain well.