Is this plant invasive?

It is native to North America but can act as an aggressive colonizer in disturbed areas.

Plant 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

horseweed — Photo by Michael J. Papay (CC BY) via iNaturalist

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

Problems to watch for

AphidsCommon
Powdery MildewCommon
Leaf SpotUncommon
RustUncommon
Tarnished Plant BugUncommon
ThripsUncommon

By symptom

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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

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Flowering

Fruiting

Foliage

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.

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This guide was generated with AI on September 26, 2026 and checked against GBIF taxonomy. It is general information, not horticultural or veterinary advice. Read about how we build these guides.