Ageratina altissima

Common Names

White Snakeroot, Richweed, Deerwort, Hardy Age, Milk Ipecac, Mist Flower, Nettle-Leaved Hemp Agrimony, White Sanicle

Summary

White Snakeroot is a native North American herbaceous perennial in the Asteraceae family that grows about 2–5 feet tall and spreads by rhizomes and seeds to form colonies. It features opposite, serrated leaves and flat-topped clusters of white flowers that bloom from July through October; nectar attracts bees, butterflies, and moths, and it favors moist, humus-rich soils in woodlands, woodland edges, and shaded areas.

All parts contain tremetol, a toxin that can cause milk sickness in humans and is poisonous to livestock. It provides nectar for pollinators and serves as a larval host for several moths. The plant can spread aggressively by rhizomes and self-seeding in disturbed soils, so deadheading spent flowers helps limit self-seeding and it is best suited for native woodland or shade plantings where wildlife value is balanced with toxicity risks.

Lifecycle

Annual, Perennial, Biennial

Height

2-5 feet

Spread

24-36 inches

Hardiness Zones

Zones 3-8

Sunlight Requirements

Ideally full sun; tolerates partial sun to partial shade

Soil Type

Moist, humus-rich loam or clay-loam soil that is well-drained.

Soil Drainage

Well-drained, Moist but well-drained

Soil pH

Slightly acidic to alkaline soils

Bloom Color

White

Bloom Time

Summer to Fall

Foliage Color

Green with gray-green and gray-silver tones

Fall Foliage Color

Yellow

Leaf Lifecycle

Deciduous

Growth Rate

Fast

Seasons of Interest

Summer and Fall

Propagation Methods

Seeds, Division

Attracts Wildlife

Bees, butterflies, other pollinators