Horseweed is a winter annual in the aster family (Asteraceae). Peak germination is in late autumn and early spring but sporadic germination may occur anytime except summer. It forms a rosette of hairy leaves. In spring, plants bolt upright 3 to 6 feet tall. Plants have a tap root with some fibrous roots making them difficult to remove. Individual flowers are small, with white ray flowers and yellow disk flowers. Do not let plants go to seed in the nursery. Control horseweed around the property to prevent spread. When hand weeding, remove completely as plants can re-sprout from broken stems. Horseweed can be managed by preemergence broadleaf herbicides. Glyphosate-resistant horseweed has been reported in areas where glyphosate-resistant crops are grown. While this species is an aggressive annual weed of waste places and disturbed areas, it is a nectar and pollen source for native bees, and its stems are used as nesting sites for solitary bees. Read more about best practices for stem-nesting bees in this NC Extension publication
Curated pairwise relationships between this plant and others in the library — who feeds
whom, who competes, who confuses the pests. Green reads as a good pairing, red as one to avoid.
No curated interactions recorded for this species yet.
Also noted by NC State
Related species the NC State Plant Toolbox flags for this plant — look-alikes to tell
apart, and plants that play a similar role in a planting. Ones we carry in the library are linked.
Full sun (6 or more hours of direct sunlight a day)
Soil pH
Acid (<6.0); Alkaline (>8.0); Neutral (6.0-8.0)
Soil drainage
Good Drainage
Available space
Less than 12 inches; 12 inches-3 feet; 3 feet-6 feet
NC region
Coastal; Mountains; Piedmont
Mature size
Height: 0 ft. 6 in. - 7 ft. 0 in. | Width: 0 ft. 6 in. - 2 ft. 0 in.
Growth rate
Medium
Maintenance
High
Canopy layer
4 - Herbaceous (3-15 ft)
Form & Appearance
Texture
Medium
Foliage
Deciduous
Leaf color
Green
Leaf type
Simple
Leaf arrangement
Alternate; Rosulate
Leaf shape
Elliptical; Lanceolate
Leaf margin
Dentate; Entire
Leaf feel
Smooth
Leaf size
1-3 inches long, < 1 inch wide
Hairs present
Yes
Leaf detail
Leaves form as a basal rosette throughout fall and winter until late spring when plants bolt upright; leaves will become progressively smaller upwards on the stem but average 2"-3 1/2" long and 1/2" wide. They occasionally have teeth along the margin otherwise are entire.
Flower color
Cream/Tan; White
Flower form
Panicle
Flower shape
Urn
Flower size
< 1 inch
Flower detail
Self-fertile Pea sized white flowers in a terminal panicle 1 1/2' long and 1/2' wide. Additoinal flowers form in the axils of leaves. Individual flowers are 2-3 mm in size and are urn to cylindrical in shape. Flowers appear for a three week period any time between mid-summer through fall.
Bloom time
Fall; Summer
Fruit color
Gold/Yellow; Gray/Silver
Fruit type
Achene
Fruit size
< 1 inch long
Fruit detail
Yellow to gray elliptical achenes with fluffy white hairs that aid in wind dispersal.
Stem color
Brown/Copper; Green; Red/Burgundy
Stem detail
Unbranched except at the top where flowers appear, light green, angular with white hairs.