Ageratina altissima

SUMMARY

White Snakeroot is an attractive fall-blooming native that enjoys part shade and thrives in woodland soil. This enthusiastic spreader reseeds prolifically and can form beautiful colonies that light up shady areas, especially if the soil is rich and moist. With an erect habit of 2′-4′, it generally does not require staking and plays well with other natives. The panicles of white flower clusters are an attractive late season food source for many bees, butterflies, and moths. Though often found growing naturally in places where it is sheltered from the hot summer sun, it is adaptable to various growing conditions. Due to the fact that this plant contains the toxin tremetol, it is not advisable to plant it where cattle or horses may graze (see Noteworthy Characteristics).

DETAILS

Other Common Names: Deerweed, Deerwort-Boneset, Milk-Sickness Plant

Family: Asteraceae

USDA Zones: 3 – 8

Life Cycle: Short-Lived Perennial, Perennial

Height: 2.00′ – 4.00′

Spread: 2.00′ – 4.00′

Sun: Part Sun – Shade

Soil: Clay, Loam, Rich Woodland Humus

Moisture: Medium-Wet, Medium, Medium-Dry

Bloom Time: July – October

Bloom Color: White

Uses: Naturalize, Rain Garden, Woodland Garden

Native Range: BONAP Map

Native Range Color Key: Dk. Green = Present in State and Native, Lt. Green= Present and Not Rare, Yellow = Present and Rare, Gold = Not Present in State, Teal = Present and Exotic, Cross-Hatched = Questionable Presence

NOTEWORTHY CHARACTERISTICS

Contains tremetol, a toxin that can prove fatal to cattle or horses if consumed
Associated with “milk sickness” which resulted in the death of Abraham Lincoln’s mother in 1818 (rare in the modern dairy industry)
Spreads enthusiastically by seeds and rhizomes, especially in disturbed soil
Grows well among other natives and can make a nice “filler” plant
Has strong branched stems that don’t require staking
Blooms late in the year around the same time as goldenrods and asters
Long bloom time; visited by bees, butterflies, and moths
Generally avoided by mammalian herbivores (deer, rabbits, etc) due to bitter foliage
Black Walnut juglone tolerant
A variety of caterpillars utilize the foliage for food
Flower clusters resemble Boneset (see images below)

Common Boneset (Left) and White Snakeroot (Right)
Though the flowers are very similar, the leaves are distinctly different which makes it easy to tell them apart.

Long, narrow leaves of Common Boneset (Left)
Wide, heavily serrated leaves of White Snakeroot (Right)

FAUNAL ASSOCIATIONS

Host plant for : Schizomyia eupatoriflorae, a small midge fly that specializes on White Snakeroot buds. Liriomyza eupatoriella, a species of fly whose larvae (leaf miners) feed on leaf tissue by mining tunnels in the foliage.
Nectar plant for: Bees,Wasps, Moths, Butterflies, Flies
Food source for: Harmostes fraterulus, a scentless plant bug that feeds on the flowers
Seeds for over-wintering birds

PESTS/DISEASES

Relatively disease and pest free.

PLEASE NOTE: Like all native plants, White Snakeroot is an important food source for many creatures. Some years they may be more affected by insects than others. However, these insects provide essential food for birds and other wildlife as part of a balanced, intricate food web. Instead of reaching for pesticides at the first sign of leaf damage, consider grabbing your magnifying glass or binoculars and observe what visitors are frequenting your amazing native plant!

A CLOSER LOOK

The ideal habitat: rich, moist woodland soil in part shade

Hairless leaves up to 5″ long are arranged oppositely and become smaller as they ascend the main stem. They have three prominent veins on the upper surface, which is most noticeable when observing the lower part of the plant. *The margins are strongly serrated and the leaves have long petioles (0.50″-2.50″).*

*Panicles of fragrant flat-topped flowerheads bloom in autumn after many other species have faded.*

COMPANION PLANTS

In order to provide the maximum benefit to pollinators, it is best to plan for a succession of blooms. This ensures that as one species fades, another begins to blossom. In this way, a constant source of nectar and pollen is provided from spring through fall. The following natives enjoy similar growing conditions to Ageratina altissima: