Pocket BotanistPlant guide
Canadian horseweed.
Erigeron canadensis
Pronounced eh-RIJ-er-on kan-ah-DEN-sis
Also known as Butterweed, Canada fleabane, Canada horseweed, Canadian Fleabane, Canadian Fleabane, Canadian Horseweed, Horse Weed, Mare's Tail, Canadian Horseweed, Cronquist, Foxtail
This hardy plant is a common sight in fields and along roadsides. It grows as an annual and is known for its tall, slender stem. You will often see it popping up in disturbed soil.
At a glance
- Care level
- Easy
- Plant type
- Annual herb
- Light
- Full sun
- Indoor light
- Direct sun
- Water
- Every 7 to 14 days
- Mature size
- 5 feet
- Growth rate
- Fast
- Hardiness
- USDA 3 to 9
- Bloom time
- Mid summer to mid autumn
Care
This plant thrives in full sun and well drained soil. Watch for wilting during extreme heat, though it is quite drought tolerant once established. It is a prolific seeder, so pull it before flowers fade if you want to limit its spread.
- Watering
- Water only when the top inch of soil feels dry to the touch.
- Feeding
- This plant generally does not require supplemental fertilizer.
- Pruning
- Remove spent flower heads to prevent unwanted self seeding.
- Repotting
- As an annual, this plant is typically not repotted.
- Soil
- Well drained, sandy or loamy
- Soil pH
- 6.0 to 7.5
- Temperature
- -20 to 35°C
- Humidity
- 30 to 70%
Safety
- People
- The plant may cause skin irritation in sensitive individuals upon contact.
- Children
- Keep away from children as the plant can cause skin irritation if handled.
- Contact allergens
- The foliage contains compounds that can cause contact dermatitis.
- Airborne allergens
- The abundant windborne seeds and pollen may trigger respiratory discomfort in sensitive people.
- Edibility
- While historically used in herbal medicine, it is not considered a food crop and should be avoided.
How to identify it
- Tall, unbranched hairy stem
- Narrow, lance shaped leaves
- Small white flower heads
- Forms a basal rosette initially
- Height
- 0.3 to 1.5m
- Spread
- 0.15 to 0.45m
- Leaves
- green, deciduous
- Flowers
- white, yellow, 0.5 to 1cm
- Fruit
- tan, Autumn
Common problems
- Powdery mildew — A fungal infection that appears as white dust on leaves during humid weather.
Growing it
- Propagation
- seed
- When to plant
- spring, autumn
Plant in sunny, open areas to mimic its natural meadow habitat.
Grows well with
- Common Milkweed — They share similar habitat requirements in open meadows.
- Goldenrod — Both species provide late season nectar for pollinators.
Similar species
- Philadelphia Fleabane — It has similar flower structures but prefers moister soil.
Science
- Family
- Asteraceae
- Genus
- Erigeron
- Order
- Asterales
- Class
- Magnoliopsida
- Native range
- North America
- Conservation
- It is considered a common weed in many regions and is not of conservation concern.
It thrives in open, disturbed habitats where it acts as an early successional species.
- Value to wildlife
- nectar source, larval host plant
- Pollinators
- bees, butterflies, beetles
- Uses
- pollinator garden, meadow restoration, herbal history
Through the year
Ecological indicators
- Salinity
- 2/9
- Soil reaction
- 5/9
- Light
- 8/9
- Temperature
- 5/9
- Moisture
- 4/9
- Nutrients
- 3/9
Taxonomy resolved against GBIF.
Questions people ask
- Is this plant invasive?
- It is native to North America but can act as an aggressive colonizer in disturbed areas.
- Does it need much water?
- It is quite drought tolerant once established.
Where the name comes from
The genus name comes from Greek words meaning early and old man, referring to the white, hair-like pappus. The species name indicates its origin in Canada.
Good to know
- It is also known as horseweed.
- The plant was once used to treat various ailments in traditional medicine.
- It is a pioneer species that quickly covers bare soil.
Is your canadian horseweed looking unwell?
This page is a general guide. Pocket Botanist diagnoses problems from a photo of your actual plant, works out watering for your light and conditions, and reminds you when care is due.
This guide was generated with AI and checked against GBIF taxonomy. It is general information, not horticultural or veterinary advice. Read about how we build these guides.