Key Facts
- Clump forming perennial with erect stems.
- Produces hood shaped blue to purple flowers in late summer to autumn.
- Prefers moist fertile soil with good organic matter.
- Performs best in part shade in warm areas and in stronger light in cool climates.
- All plant parts are poisonous to humans and animals.
- Commonly grown for late season color in mixed borders.
- Propagated by division or by seed with a period of cold stratification.
Monkshood (Aconitum carmichaelii) is a clump forming perennial prized for its hood shaped blue to purple flowers that appear in late summer to autumn. It adds strong late season color to mixed borders but all parts are highly poisonous so handle with gloves and keep plants away from children and pets.
Identification
Monkshood produces erect stems from a clumping base and typically reaches 3 to 5 feet tall with a spread of about 1 to 2 feet. Flower spikes of hood shaped blue to purple blooms appear in late summer into autumn, often between August and October in northern climates.
Where to grow and best uses
Use Monkshood toward the middle or back of mixed borders and in woodland edges where its height and late blooms provide structure and seasonal color. It is suitable for USDA zones 4 to 7 and performs well in temperate gardens when placed where roots stay cool and moist.
Planting and timing
Plant bare root or container grown plants in spring or autumn in prepared soil rich in organic matter. Space plants about 12 to 24 inches apart to allow for a 1 to 2 foot clump. Division is best done in spring or autumn to renew older clumps and maintain vigor.
Soil, light and watering
Monkshood prefers moist fertile loam rich in humus and tolerates heavier soils if not waterlogged. It prefers part shade, taking stronger light in cool climates and more shade in warm areas. Consistent moisture encourages flowering; dry soil leads to stunted plants and fewer blooms while poor drainage can cause crown rot.
Maintenance and after flowering care
Remove spent flower stalks to tidy the border and reduce self-sown seedlings. Apply a layer of organic mulch to conserve soil moisture and feed plants with compost or a balanced fertilizer for best late season display. Divide congested clumps in spring or autumn to restore vigor.
Controlling spread and propagation
Monkshood forms clumps rather than aggressive runners and generally expands slowly to fill a 1 to 2 foot space. Control is by lifting and dividing sections of the clump every few years. Propagate by division in spring or autumn or by seed after a period of cold stratification; seed-grown plants may be slow to flower.
Toxicity and safety
All plant parts are poisonous, containing aconitine and related alkaloids. Skin contact can cause numbness or irritation and ingestion can produce serious cardiac and neurological symptoms. Wear gloves when handling, keep plants away from children and pets and consult local poison control or medical services for exposures.
Frequently asked questions
- How fast does Monkshood grow?
- Monkshood has a moderate growth rate and can reach its typical 3 to 5 foot height in a growing season when established in moist, fertile soil.
- Where is the best place to plant Monkshood?
- Plant in part shade at the middle or back of borders and woodland margins where roots stay cool and moist. It suits temperate gardens in USDA zones 4 to 7.
- Is Monkshood poisonous?
- Yes. All parts are highly poisonous. Wear gloves when handling and keep plants out of reach of children and pets. For exposures contact local poison control or medical services.
- How do I propagate Monkshood?
- Propagate by division in spring or autumn for reliable results. Seed is possible but typically requires cold stratification and may be slow to reach flowering size.
- How do I control its spread?
- Control comes from periodic division and removing unwanted seedlings. Monkshood is clump forming and does not usually behave as an invasive spreader.
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