Aconitum napellus aka Monkshood

Aconitum napellus, or monkshood, belongs to the buttercup family, Ranunculaceae. It is a perennial with tuberous roots and upright growth. Kew lists its native range as southern Wales and southwest England. Other sources give a wider range across Europe and Asia. RHS does not list it as native to Britain or Ireland. These sources differ on its native status and range. It grows in damp meadows, shady sites, and moist mountain areas.

Garden plants reach about 2–5 feet (0.6–1.5 metres) tall. Their spread reaches about 1.6 feet (0.5 metres). Firm, leafy stems rise from a clump of roots. The dark green leaves have five to seven deep, toothed lobes. The leaves die back at the end of the season. Dense flower spikes top the stems in July and August. The flowers range from deep purple-blue to violet. Each flower has a large upper sepal shaped like a hood. This shape gave the plant its common name, monkshood.

Grow it in rich soil that stays moist through summer. Good drainage helps keep the roots from sitting in wet soil. RHS also lists poorly drained soil as suitable. Partial shade suits it, though cool sites can offer full sun. Afternoon shade helps where summers turn hot. It needs cool nights and can struggle in summer heat. It grows in clay or loam across acid, neutral, and alkaline soils. Sources rate it for USDA zones 3–7 and UK hardiness H7. Plants may take two to five years to reach full size.

Monkshood suits flower borders, cottage gardens, and lightly wooded sites. Moist ground beside streams or ponds can also suit it. Its flowers attract butterflies, and deer and rabbits tend to avoid it. Tall stems may need support in exposed sites. Cutting spent flower stems may prompt more bloom later. Division is possible, but plants can take time to settle again. Aphids sometimes attack it, though serious pest trouble is uncommon. Stem or crown rot, powdery mildew, and Verticillium wilt can occur.

Every part is highly poisonous to people and pets. Skin contact can cause numbness, so wear gloves when handling it. Keep it away from small children and vegetable plots. Reports of edible cooked roots are unsafe grounds for eating it. The roots contain more poison than the leaves. Historical medicinal use does not make home use safe. PFAF states that medicinal use needs a skilled practitioner's guidance.