Hoary Vervain grows erect on stout, square stems, up to 3 feet tall. The inflorescence is a few tall spikes branching from the main stem. The stems are dusty looking with long whitish hairs, hence the common name. The individual flowers are blue, quite small, 1/8" to 1/4" wide, 5-parted, and open individually on the densely packed spike from bottom to top with only a few open at one time on each spike. Leaves are opposite, oval to elliptical with sharp coarse teeth.

Habitat: Hoary Vervain prefers full sun in dry to moderate moisture sites such as disturbed areas, prairies, sandy fields - a more dry environment than the other two species noted here. Comparison: The differences between this plant and Blue Vervain, V. hastata, are that V. hastata has lance shaped leaves with an outward facing basal lobe and no hairs on the stem. The flowers are similar, as they are to White Vervain, V. urticifolia, but there the inflorescence is much different, being a loosely spreading panicle of many flower spikes. The species name, stricta, refers the erect or rigid stem.