Hemp nettle Galeopsis tetrahit
IDENTIFICATION — This 1- to 2-ft.-tall branching annual is a member of the mint family so it has square stems. But it’s easy to distinguish from its cultivated relatives by stiff bristly hairs along the stems and on the leaves. Also, look closely at the stem and you’ll notice that there is a bulge just below each set of leaves.
White, pale pink or purple flowers open in early to late summer. These flowers are clustered in the leaf axils near the top of the plant. After the flowers fade, you’ll find seeds contained in a small spiny case.
FAVORITE CONDITIONS — Hemp nettle grows in full-sun to part-shade areas that are occasionally tilled. It prefers vegetable and flower gardens. You’ll rarely find the seeds sprouting in lawns or other areas where it has to compete with dense grasses.
CONTROL —Try to keep this annual from setting seeds. Cut it down as it starts to bloom to prevent seeds from forming. However, continue to cut it off because it will still try to flower. Young plants are easy to hoe out of the soil. Mature plants have a branched taproot that makes pulling difficult. Nonselective herbicides, such as Round-up®, will kill it. And selective broadleaf herbicides, the kinds used in lawns, are also effective.