Ageratina occidentalis aka Western Snakeroot

Ageratina occidentalis is also known as western snakeroot. It is a perennial, so it lives for more than one year. It belongs to the aster family, Asteraceae. Its native range covers the western United States. It also includes northern Baja California, Mexico. Records list Washington, Oregon, and California. They also list Idaho, Montana, Nevada, and Utah. It grows in temperate regions, which have mild climates. It is not native to Britain or Ireland. Eupatorium occidentale is an older name for the same species.

The plant grows about 2.3 feet (0.7 metres) tall. This makes it a low choice for a woodland garden. Records from California place it in several kinds of forest. These include yellow pine, red fir, and lodgepole pine forests. It also grows in redwood and Douglas-fir forests. Reported sites lie at 6,230–10,830 feet (1,900–3,300 metres) above sea level. These forest records help guide its place in woodland gardens.

Western snakeroot blooms late in the season, from August to September. Each flower has both male and female organs. Insects pollinate the flowers. The plant is self-fertile: it can set seed with its own pollen. The supplied species records do not describe flower colour or fruit. Nor do they give leaf or stem details for this species. The stated height helps show its size in a planting. The records give no width for a full-grown plant.

Grow it in sun or part shade. This includes woodland shade where patches of light reach the ground. The listed garden sites also include a sunny woodland edge. It accepts sand, loam, and clay soils that drain well. The soil must hold moisture but still let water drain. It suits soils that are slightly acid, neutral, or slightly alkaline. Plants For A Future lists USDA hardiness zones 5–9. Sow seed in a cold frame in spring. Give the seed a light covering. Move young seedlings to their own pots when large enough. Plant them outdoors in summer. You can also divide well-grown plants in spring.

Plants For A Future lists no known edible uses. It reports use on the body for rheumatism and swelling. This is a reported use, not proof that it helps. The same source lists no known hazards or other uses. A lack of reported hazards does not mean it is safe to eat. The source does not flag it as weedy. The supplied records name no specific pests or diseases.