Marrubium vulgare aka Horehound

Marrubium vulgare, or white horehound, belongs to the mint family, Lamiaceae. Its native range covers Macaronesia, Europe, and the Mediterranean to the central Himalaya. It has spread beyond this range into much of the Americas. This deciduous perennial forms upright clumps that spread at a slow pace. Garden plants reach about 1–2 feet [0.3–0.6 metres] tall and wide. The RHS gives a smaller upper size of about 1.6 feet [0.5 metres]. Plants take two to five years to reach full size.

White hairs coat the square stems and give them a pale look. The simple leaves grow in opposite pairs along each stem. They are round to egg-shaped, with scalloped edges and a wrinkled surface. Soft hairs cover the grey-green blades, with woolly growth beneath. Fresh leaves have a musky scent that fades as they dry. Small white flowers form tight whorls at the upper leaf axils. Flowering runs from June to November, according to NC State. Bees and other pollinators visit the blooms. The fruit is a schizocarp that splits into four dry, single-seeded nutlets. Seeds ripen from August to October.

Grow horehound in full sun and soil that drains well. It prefers dry, sandy ground but also tolerates poor or moist soil. The RHS lists acid, neutral, and alkaline soils as suitable. Keep excess winter moisture away from the roots. NC State lists USDA zones 3–9; the RHS rates it H6. Use it in herb beds, gravel gardens, or informal borders. It also suits banks, slopes, and wildflower meadows. Its pale leaves and long flower season add garden interest.

Horehound has few major pest or disease problems, but it can become weedy. Livestock tend to leave it while grazing nearby plants, which helps it spread. Remove old flower stems when you do not need seed. Cutting back after bloom can also bring a fresh crop of leaves. Grow new plants from seed or take softwood cuttings in spring.

People use the bitter leaves to flavour tea, beer, liqueurs, and hard sweets. The plant also has a long history in folk cough remedies. These uses do not make large doses safe. PFAF warns that large amounts can affect heart rhythm, blood pressure, and blood sugar. It advises avoiding use during pregnancy and breastfeeding. People taking blood-sugar-lowering drugs should also avoid it.