Northern willowherb grows upright, commonly up to 4 to 6 feet tall. Stems are solitary or in clusters, and are rarely branched above. Each leaf is 2 to 8 inches long, serrated, oppositely arranged on lower foliage, but sometimes alternately arranged on the upper part of the stem. Leaves are sessile or with very short petioles.
Flowers are solitary and occur at the end of 1 to 2 inch long pedicels (flower stalks). Flowers are pink with 4 deeply lobed petals
Favorable environment notes:
Northern willowherb is very adaptable. It can be found in disturbed areas, moist areas, dry areas, wetlands and roadsides. This weed is especially problematic in container and field nurseries, gravel areas and Christmas tree plantings.
Seeds are borne in long capsules (roughly 5cm long). Upon maturity, the capsule splits from the apex and releases seeds with white tufts of hairs, which aids in wind dispersal. Seeds germinate in full sun, shady areas and at a wide range of temperatures making this weed very adaptable to nursery environments. Sanitation is essential to maintaining control over the spread of northern willowherb. Keep gravel areas and non-crop areas of the nursery free of weeds that could produce more seed sources by using traditional herbicides. Overwintering structures on the soil surface called turions can quickly become seed sources in warm spring weather. Herbicides are not effective in controlling turions. Hand removal of these structures in the fall and winter can greatly reduce the spread of seed in nursery settings.