Eupatorium cannabinum aka Hemp Agrimony

Eupatorium cannabinum is also called hemp agrimony. It belongs to Asteraceae, the daisy family. This upright perennial forms clumps and lives for years. RHS lists it as native to Britain and Ireland. Kew also gives its native range as northeastern India to Assam. PFAF lists a wider range across Europe, Asia and northwestern Africa. It grows by streams, in damp lowlands and in woods. These sites help explain why it prefers moist garden soil.

Garden plants grow about 3.3–4.9 feet [1–1.5 metres] tall and wide. They take two to five years to reach full size. The stems have a red tint and dark green leaves. Each leaf has narrow leaflets. The leaves are palmately divided: their leaflets spread from one point. Small flowers form dense, round groups at the stem tips. They range from pale pink to purple. The main show comes in late summer and early autumn. Butterflies and other insects visit the blooms.

Grow hemp agrimony in full sun or partial shade. RHS suggests moist soil, including clay and loam. The soil can drain well or hold excess water. RHS lists acid, neutral and alkaline soils as suitable. Yet PFAF says wild plants avoid acid soils. RHS gives it a cold-hardiness rating of H7. PFAF lists USDA zones 4–8. It suits both exposed and sheltered sites. Its height helps it fit among other border plants. Leave room for its full width when placing it.

Use it in wildlife gardens, wildflower meadows or informal borders. Damp woodland edges and bog gardens suit it too. RHS also suggests gardens by the coast. Plants can spread fast, so leave space around each clump. PFAF does not flag it as a weed. Cut off spent blooms when the flowering season ends. Divide plants in spring, or sow seeds in containers in a cold frame. Slugs and aphids may attack it. RHS reports few problems with disease.

PFAF records no known edible uses for this species. It notes past use as medicine for fevers and other ailments. This does not mean it is safe for home treatment. PFAF warns that its alkaloids need expert oversight. It also notes old uses for the leaves and juice. People used leaves to help keep mould off bread. They rubbed leaf juice on animals to repel insects.