Pycnanthemum muticum aka Clustered Mountain Mint

Pycnanthemum muticum belongs to the mint family, Lamiaceae. It is a perennial, so it lives for many years. Names include blunt mountain mint and short-toothed mountain mint. It is native to the eastern and east-central United States. It grows in woods and thickets, including dry Texas woods. It grows upright and bushy, and sheds its leaves each year. Garden heights range from about 1.6–4 feet [0.5–1.2 metres]. Plants spread about 1.6–3.3 feet [0.5–1 metre]. RHS gives smaller heights than NC State's 3–4 feet [0.9–1.2 metres].

Square stems bear pairs of broad, green leaves with toothed edges. Each leaf has a rounded base. Its blade is oval or shaped like a lance. Crush the leaves to release a strong scent like spearmint. Rhizomes, or stems below ground, help it spread into patches. It can grow strongly where conditions suit it. NC State calls it weedy, though not invasive. Give it room where spreading patches fit the garden plan. Prune roots with a spade in spring to limit spread.

Small flowers with two lips grow in tight groups. These sit near the tips of the stems. The flowers range from near-white to very pale pink. Silver bracts sit below them and provide much of the show. Sources give bloom dates between June and September. Some reports place the start of bloom earlier. NC State gives June to August. Missouri Botanical Garden gives July to September. Black capsules appear in September and October. Bees, butterflies, and other insects seek nectar in the flowers. The plant also hosts the young of the wavy-lined emerald moth.

Grow it in full sun or part shade. It prefers moist soil that drains well, but withstands drought. RHS lists chalk, clay, loam, and sand as suitable soils. It accepts acid, neutral, and alkaline soil as well. Hardiness ratings are USDA zones 4–8 and UK H7. Plants take about two to five years to reach full size. Grow new plants from seed or divide them in spring. Cut old stems in late autumn or early spring. It needs little care beyond keeping unwanted spread in check.

Use it in native gardens, meadows, herb beds, and borders. Plant groups to show off the silver bracts during bloom. It also suits cottage gardens and rain gardens. Gardens for wildlife and pollinators suit it too. Chicago Botanic Garden reports that it resists deer browsing. Serious pest and disease problems are rare, though rust can occur. You can brew the leaves and flowers into tea. The leaves also serve as a mint substitute in cooking. Plants For A Future lists no known hazards or medicinal uses.