Verbena hastata aka American Blue Vervain

Verbena hastata, or blue vervain, is a North American wildflower. Its native range spans Canada and the United States. It belongs to the verbena family, Verbenaceae. This perennial grows in wet meadows, marshes, and riverside ground. It also occurs in ditches, thickets, and disturbed sites. Plants form upright clumps and may be short-lived. They spread through slow-growing rhizomes and seeds.

Garden plants reach about 2–5 feet [0.6–1.5 metres] tall. Some reach 6 feet [1.8 metres]. Sources give spreads of 1–3.3 feet [0.3–1 metre]. The stiff stems branch near the top. They have square cross sections and fine hairs. Stems may be green or tinged with red. Narrow green leaves grow in pairs along each stem. Their edges have teeth, and their veins stand out. Leaves can reach 0.5 feet [0.15 metres] long. The plant loses its foliage in winter.

Tall branches hold groups of thin flower spikes. These form a shape like a branching candle stand. The small, tubular flowers have five spreading lobes. Their shades range from violet-blue to pinkish purple. Bloom lasts from July to September, sometimes into October. Flowers open from the base of each spike upward. Only a few flowers open at once. The calyx remains around four reddish-brown nutlets. Bees gather nectar and sometimes pollen from the flowers. Butterflies and hummingbirds also visit. Cardinals, sparrows, and juncos eat the seeds. The plant hosts verbena moth and common buckeye larvae.

Grow blue vervain in full sun and moist soil. It also accepts part shade and periods of wet soil. Clay, loam, and sand can all suit it. It tolerates acid, neutral, and alkaline ground. RHS also reports drought resistance and accepts well-drained soil. Its hardiness ratings are USDA 3–8 and RHS H5. It suits borders, rain gardens, pond edges, and meadow plantings. Seeds, division, and softwood cuttings provide ways to propagate it. Pinching shoot tips can help stems branch. Plants may self-seed where conditions suit them.

Care needs are low, with few serious pest or disease problems. NC State lists southern bacterial wilt as a possible problem. Rabbits may eat the leaves, though most mammals avoid their bitterness. Reported food uses include cooked seeds and tea from leaves. The plant also has a history of medicinal use. These uses do not establish its safety or effectiveness. Large doses can cause vomiting and diarrhea. It may interfere with blood-pressure drugs and hormone therapy.