White Snakeroot

Ageratina altissima

White snakeroot is fall's great shade plant. In September and October, it covers itself with bright, clean white flat-topped flower clusters that glow in the dim light under trees when other plants have checked out for the season. The flowers are small individually but arranged in such dense clusters that the plant reads as a cloud of white from any distance. Against dark woodland soil and the first falling leaves, the effect is genuinely beautiful. A plant that colonizes freely by seed in moist, shaded conditions -- which means it can be a vigorous spreader in favorable sites. Managed thoughtfully, it fills the fall shade garden role that no other plant handles as well. The deeply toxic foliage makes it completely unpalatable to deer and one of the most deer-proof shade perennials available. An important late-season nectar source for monarchs moving through woodland edges.