Epilobium hirsutum aka Great Hairy Willow Herb

Epilobium hirsutum is known as great willowherb or hairy willowherb. It belongs to the evening primrose family, Onagraceae. Its native range spans temperate Eurasia and parts of Africa. It is native to Britain and Ireland. This herbaceous perennial sheds its leaves for winter. It grows beside streams, in marshes, and in ditches. It also occurs in wet lowlands and along roadsides.

Garden plants reach about 5–8 feet [1.5–2.5 metres] tall. Their spread reaches about 3–5 feet [1–1.5 metres]. Upright green stems branch and bear a thick coat of hairs. Dark green leaves are narrow, pointed, and lance-shaped. Most grow in opposite pairs, without leaf stalks. Each leaf has toothed edges and clear, deep veins. Underground rhizomes spread outward and form thick masses of roots. This growth can make established clumps hard to control.

The RHS places flowering in summer, despite NC State's winter listing. Pink flowers have pale centres and four notched petals. Each bloom measures about three-quarters of an inch across. Flowers grow in leaf axils near the stem tops. Hoverflies and other insects visit them. Thin, hairy seed pods follow the flowers. These reach one to three inches long before splitting open. White hairs help the many small seeds travel on wind.

Full sun suits this plant best, though it tolerates partial shade. It favours damp or wet soil and tolerates brief flooding. It also grows in moist soil that drains well. Sand, loam, clay, and chalk can all suit it. It accepts acid, neutral, and alkaline soil. The RHS rates its cold hardiness as H7. Plants reach mature size in two to five years. Divide clumps in spring or autumn, or grow from seed. Cut dead growth back at the year's end.

Wildlife gardens and damp meadows offer space for its spreading roots. Its flowers provide a draw for visiting pollinators. Yet it can spread aggressively beyond its intended place. Some northern United States regions class it as invasive. Slugs and snails may feed on it. Rust and powdery mildew may also affect plants. Reports describe leaves used for tea and as an astringent. These uses do not establish that eating it is safe. Plants For A Future also records poisoning reports involving severe convulsions. Those reports warrant caution about using the leaves as food or medicine.