Wildflower (forb) · Asteraceae
Canadian horseweed
Conyza canadensis · includes its varieties and subspecies
Canadian horseweed is recorded as native to 46 states and territories in Kew’s World Checklist of Vascular Plants and USDA PLANTS, and recorded in 2,083 counties of those states by USDA PLANTS.
Key facts · USDA PLANTS
Canadian horseweed at a glance
- Native in
- 2,083 counties, across 46 states and territories
- Estimated cold hardiness
- Zone 12b PLANTS minimum temperature 52°F
- Mature height
- 5 ft PLANTS mature height
- Light and water
- Full sun (shade-intolerant) Medium water use
Estimated cold hardiness: zone 12b. PLANTS gives a minimum temperature of 52°F; zone 12b winters bottom out at 55°F, the coldest half-zone that stays within that limit.
Canadian horseweed is recorded as native to 46 states and territories in Kew’s World Checklist of Vascular Plants and USDA PLANTS, and recorded in 2,083 counties of those states by USDA PLANTS.
Counties where it is native
The 15 counties with the most ZIP codes among the 2,083 where it is listed.
Native counties by state
- Alabama 9 counties
- Arizona 15 counties
- Arkansas 61 counties
- California 47 counties
- Colorado 32 counties
- Connecticut statewide record
- Florida 62 counties
- Georgia 35 counties
- Idaho 24 counties
- Illinois 102 counties
- Indiana 67 counties
- Iowa 20 counties
- Kansas 105 counties
- Kentucky 52 counties
- Louisiana 61 counties
- Maine 15 counties
- Massachusetts 14 counties
- Michigan 70 counties
- Minnesota 67 counties
- Mississippi 81 counties
- Missouri 109 counties
- Montana 29 counties
- Nebraska 52 counties
- Nevada 16 counties
- New Hampshire 9 counties
- New Jersey 19 counties
- New Mexico 27 counties
- New York 33 counties
- North Carolina 97 counties
- North Dakota 31 counties
- Ohio 71 counties
- Oklahoma 35 counties
- Oregon 27 counties
- Pennsylvania 66 counties
- Rhode Island 5 counties
- South Carolina 42 counties
- South Dakota 25 counties
- Tennessee 40 counties
- Texas 131 counties
- Utah 29 counties
- Vermont 9 counties
- Virginia 96 counties
- Washington 25 counties
- West Virginia 36 counties
- Wisconsin 68 counties
- Wyoming 17 counties
Growing traits
Values from the PLANTS characteristics record. “Not recorded” means PLANTS has no value; nothing here is estimated except the zone.
Growth
- Growth habit
- Forb/herb
- Duration
- Annual, Biennial
- Mature height
- 5 ft
- Growth rate
- Rapid
- Growth form
- Single Crown
- Shape
- Erect
- Lifespan
- Not recorded
- Active growth period
- Spring, Summer, Fall
Light and water
- Shade tolerance
- Intolerant (full sun (shade-intolerant))
- Moisture use
- Medium water use
- Drought tolerance
- Low
- Tolerance of waterlogged soil
- Low
- Precipitation range
- 14 to 55 in per year
Soil
- Soil textures
- Coarse, medium and fine
- pH range
- 4.8 to 7.2
- Lime (CaCO₃) tolerance
- Low
- Salinity tolerance
- None
- Fertility requirement
- Medium
- Minimum root depth
- 6 in
Climate
- Minimum temperature
- 52°F
- Estimated cold hardiness
- Zone 12b and warmer
- Minimum frost-free days
- 60
- Fire tolerance
- Low
Flowers, leaves and fruit
- Flower color
- White
- Showy flowers
- Yes
- Bloom period
- Indeterminate
- Foliage color
- Green
- Showy in fall
- No
- Keeps leaves
- No
- Fruit color
- Brown
Other
- Toxicity
- None
- Nitrogen fixation
- None
- Nursery availability
- No Known Source
- Family
- Asteraceae
- PLANTS symbol
- COCA5
Source & data date
- Source
- USDA NRCS PLANTS Database: county distribution records, native status and plant characteristics. CC0 (public domain dedication, per the data.gov catalog record).
- Kew’s World Checklist of Vascular Plants (WCVP): native or introduced status by state. CC BY 3.0.
- USGS US-RIIS (ver. 2.0): species listed as introduced are excluded. CC0.
- Citation
- USDA, NRCS. 2026. The PLANTS Database (https://plants.usda.gov, 11/04/2026). National Plant Data Team, Greensboro, NC USA.
- Govaerts R. (ed.) (2026). WCVP: World Checklist of Vascular Plants. Facilitated by the Royal Botanic Gardens, Kew. Data file dated 2026-06-04, http://sftp.kew.org/pub/data-repositories/WCVP/ (retrieved 2026-11-04). Paper: Govaerts R. et al. (2021) The World Checklist of Vascular Plants, a continuously updated resource for exploring global plant diversity. Scientific Data 8, 215.
- Data date
- Retrieved from PLANTS on November 4, 2026; WCVP data file dated June 4, 2026.
- Scope
- Conyza canadensis (PLANTS symbol COCA5), including 3 varieties and subspecies folded into the species.
- Method
- A species is listed when it is recorded as native to the state in Kew’s World Checklist of Vascular Plants and USDA PLANTS, and recorded in the county by USDA PLANTS. Species PLANTS labels both native and introduced are listed separately. Full method · All sources