Blue Vervain (Verbena hastata) is a stunning wildflower that can reach heights of up to 1.5 m. Native to North American and cold hardy to Zone 3, it grows in every American state and in every Canadian province except Alberta and Newfoundland. It’s a terrific addition to a butterfly garden, particularly in the United States. It’s a food source for the larvae of the common buckeye butterfly, which primarily flies in the U. S. A.
Recognizing Blue Vervain
Also known as swamp vervain and swamp verbena, it’s no surprise that blue vervain grows naturally in the moist soils found along riverbanks, marshes, ditches, and shores. In a home garden, it does particularly well in low-lying areas and around the edges of ponds.
According to the United States Department of Agriculture, blue vervain has square stems that might be green or red and are often hairy. Pairs of leaves grow along the stems. Leaves are long and narrow (about 15 cm by 2.5cm). They are also toothed.
The upper stems of the plant branch out into panicles, which are clusters of flowers on spikes. Each spike is about 13 cm long. While a single spike will produce dozens of blossoms, only a few flowers open at one time. Over the course of the blooming period (June through August), flowers will begin opening from the bottom of the spikes and progress to the top. The tiny blue-violet flowers are only about 0.5 cm across. The Illinois Wildflowers website describes the flowers as having, “a blue-violet corolla with 5 spreading lobes, a short-tubular calyx with 5 narrow teeth, 4 inserted stamens, and a pistil. The calyx is grayish green to dark red and about one-half as long as the corolla.”
About six weeks after blooming, each bloom changes to four “nutlets.” The nutlets are reddish brown and tiny–just 2 mm long. Nutlets can be collected for plant propagation. However, Kansas State University cautions about plant identification. There are several other species of verbena that look quite similar to blue vervain, including hoary vervain (V. stricta), narrow-leaved vervain (V. simplex), pink vervain (V. pumila), nettle-leaved vervain (V. urticifolia), and fanleaf vervain (V. plicata). While each could be a lovely addition to your garden, only blue vervain will attract the common buckeye butterfly.
Growing Blue Vervain
Blue vervain isn’t the easiest wildflower to introduce to your garden. The United States Department of Agriculture explains that blue vervain is best propagated by seed, which needs to be cold stratified and started indoors. But once established, blue vervain will self-seed for an impressive garden display.
Start by collecting nutlets from wild plants in late summer or early fall. Spread the nutlets out over a protected indoor surface and let them dry for several days. Once dry, the nutlets need to be crushed lightly in order to remove their seeds.
Seeds must be cold stratified in order to germinate. Mix the seeds with wet sand or peat moss and seal everything into an airtight container or bag. Store in the refrigerator, at 3-4 degrees Celsius, for three months. When the cold stratification period is over, create a mix of one part sand to two parts soil. Put the soil mix into seed trays or pots and lightly press the seed mix into the soil. Keep the pots under grow lights, at about 15-26 degrees Celsius. The seeds should germinate in about 5-15 days.
When ready to plant out, choose a spot that has full sun to part shade and rich, moist soil. Once established, blue vervain requires little care other than pinching the tops back a few times during the growing season. This encourages bushier, fuller growth.
Blue vervain blooms in mid- to late summer. Bloom time lasts for about 4-6 weeks as the blossoms gradually unfurl up the plant’s spikes.
Blue Vervain and Butterflies
Blue vervain is a host plant for the common buckeye butterfly, which is quite striking in appearance. The Butterflies and Moths of North America website describes these butterflies as being primarily brown with distinctive markings. The upperside of the both the forewings and the hindwings have a pair of eyespots, one small and one larger pair. It’s speculated that the eyespots are a way to scare away predators.
The forewings also each have two orange cell bars and a white band. The underside of the wings is paler in colour, particularly in the summer, but the markings are repeated.
Common buckeye butterflies are most often found in the southeastern United States and in California, with some sightings in the southern western and midwestern states. The Butterflies and Moths of North America website says that these insects migrate north in the summer to colonize the northern states and southern Canada. However, the Canadian Biodiversity Information Facility website says that the insects are “normally only a rare stray in Canada[.] But in good migrant years temporary colonies can become established, and the Common Buckeye becomes locally common for one season.”
Part of the fun of establishing a butterfly garden is to see which species visit. Why not plant some blue vervain to see if the gorgeous common buckeye butterflies fly on through?
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