Purple deadnettle

Purple deadnettle (Lamium purpureum) is a low winter annual in the mint family with the characteristic square (four-sided) stems of mints. Leaves are opposite, triangular to heart-shaped, scalloped or toothed on the margins, and conspicuously stalked (petioled); the upper leaves crowd toward the stem tips and are tinged reddish-purple, giving the top of the plant a purplish cast. Small pinkish-purple tubular two-lipped flowers appear in the leaf axils near the stem tips. It is easily confused with henbit, but purple deadnettle's upper leaves are distinctly petioled and crowded into a purple-tinged terminal cluster, whereas henbit's upper leaves clasp the stem directly without stalks; crushed foliage may have a faint, not strongly minty, odor.

In turf, purple deadnettle creates conspicuous purplish-green patches of upright, leafy growth in late winter and early spring that stand out against still-dormant or slow-growing grass and disrupt uniformity. Dense stands crowd thin cool-season turf during the early-season window, and the flush of growth and flowering produces an untidy, weedy appearance until the plants die back in late spring, by which point they have already reseeded.

Purple deadnettle is a winter annual reproducing by seed. Seeds germinate in late summer and fall as soils cool, the plants overwinter as low rosettes or small green plants, then resume growth, flower, and set seed in early spring before dying out as temperatures rise into summer. The abundant seed carries the population to the next fall germination flush, completing the winter-annual cycle.

It is favored by thin, open, or dormant turf in fall and by cool moist conditions, and is common in newly seeded areas, gardens, field edges, and any turf that is sparse going into winter. Bare or weak turf in autumn provides the open ground its fall-germinating seedlings exploit, so under-fertilized, recently disturbed, or thin stands are the most readily invaded.