Pycnanthemum virginianum aka Virginia Mountain Mint

Pycnanthemum virginianum is a perennial in the mint family. Its common names include American mountain mint and mountain mint. It comes from eastern Canada and the central and eastern United States. Despite its name, it does not favour mountain sites. It grows in wet meadows, swamps, and beside streams and ponds. Other habitats include gravel shores and both dry and wet thickets.

In gardens, it grows 2–3 feet [0.61–0.91 metres] tall. Its spread reaches 1–1.5 feet [0.30–0.46 metres]. Many upright branches form a dense, bushy plant. Green or red stems have four clear angles. Small white hairs grow along their ridges. The narrow green leaves grow in opposite pairs. They lack stalks and have smooth edges and pointed tips. Crushed leaves give off a strong mint scent. Rhizomes spread out from the roots and form small colonies. Growth proceeds at a moderate pace.

Small white flowers form flat clusters at the stem tips. Some flowers have purple spots. Each flower has a tube and two lips. The flowers open from the cluster's edge toward its centre. Only a few open at once within each head. Bloom runs from July to September, though Chicago lists July to August. Bees, wasps, flies, beetles, and small butterflies visit the flowers. Each flower yields four tiny black seeds with pitted surfaces. Wind carries the seeds away, and they appear in fall.

Grow this plant in full sun or partial shade. It prefers moist soil but also grows in average garden soil. It accepts sand, loam, clay, and stony ground with good drainage. Its listed USDA hardiness range is zones 3–7. Care needs are low, with a moderate need for water. Dry spells can make the lower leaves yellow and drop. Rich growing conditions can lead to vigorous spread. Dry soil slows that spread. It suits herb beds, borders, meadows, and open pond edges. Its flowers also suit gardens grown for bees and butterflies.

Serious pest and disease troubles are few. Leaf-chewing insects and mammals seldom damage this plant. Stressed plants may develop rust. Leaves and flower buds have reported food uses, raw or cooked. They can flavour salads and other foods. Fresh or dried leaves also make a mint-like tea. Traditional uses include leaf tea for digestive and cold symptoms. Leaf poultices have also served as a treatment for headaches. These reports do not establish that such treatments work. PFAF lists no known hazards but warns against use during pregnancy. It cites a possible risk of miscarriage.