Cirsium arvense, Canada thistle
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Herbaceous

Cirsium arvense

Canada thistle

Asteraceae

Europe, western Asia, northern Africa

At a Glance

TypePerennial
HabitUpright
FoliageDeciduous
Height24-60 inches (60-150 cm)
Width24-48 inches (60-120 cm)

Growing Zones

USDA Hardiness Zones

2 - 9
Zone 2
Zone 3
Zone 4
Zone 5
Zone 6
Zone 7
Zone 8
Zone 9
These zones indicate the coldest temperatures this plant can typically survive.
Frost Tolerancehardy

Key Features

Attracts Pollinators
Attracts Butterflies
Deer Resistant
Drought Tolerant
Fragrant (light)
Maintenancehigh

Overview

Cirsium arvense is a deep-rooted, colony-forming herbaceous perennial in the daisy family (Asteraceae) reaching 24–60 inches (60–150 cm) tall with a 24–48 inch (60–120 cm) spread per individual stem cluster, expanding indefinitely via lateral roots. Stems are erect, branching in the upper half, smooth to slightly hairy, and lack the spiny wings found on Carduus and some other thistle genera. Leaves are oblong to lance-shaped, 3–8 inches (8–20 cm) long, with irregularly lobed and spiny-toothed margins, dark green above, lighter and sometimes slightly hairy beneath. The species is dioecious — male and female flowers are borne on separate plants. Flower heads are small, 0.5–0.75 inch (12–18 mm) in diameter, numerous, borne in loose terminal clusters. Florets are pink to lavender with a light vanilla-like fragrance. Female heads produce seeds with a feathery (plumose) pappus for wind dispersal. A single female plant produces 1,000–5,000 seeds annually. The extensive lateral root system spreads 10–20 feet (3–6 m) per year at depths of 6–36 inches (15–90 cm), with adventitious shoots emerging every 4–12 inches (10–30 cm) along the roots. Root fragments as small as 0.25 inch (6 mm) regenerate. Listed as a noxious weed in 43 U.S. states and all Canadian provinces, and is classified as a federal noxious weed in the United States.

Native Range

Native to Europe, western Asia, and northern Africa, occurring in agricultural fields, pastures, meadows, roadsides, and riparian areas from sea level to approximately 8,000 feet (2,400 m). Despite the common name, the species is not native to Canada; it was introduced to North America in the 1600s and is now established across all 50 U.S. states and all Canadian provinces.

Suggested Uses

Used extensively in noxious weed management training and integrated weed management curricula at county, state, and federal levels. Studied in invasion biology, root physiology, and biological control research. Flowers visited by honeybees and native bees; some beekeepers utilize thistle bloom as a nectar source. Seeds consumed by goldfinches and pintail ducks.

How to Identify

Distinguished from native Cirsium species by the absence of spiny wings on the stems, the small flower heads 0.5–0.75 inch (12–18 mm) in diameter (native thistles typically have heads 1–2 inches / 25–50 mm across), and the colonial growth habit from creeping lateral roots. Distinguished from Carduus species by the feathery (plumose) pappus bristles (versus simple, unbranched bristles in Carduus). The dioecious flowering habit is unusual among thistles; male heads have protruding stamens, while female heads have protruding styles.

Appearance

Size & Dimensions

Height2' - 5'
Width/Spread2' - 4'

Colors

Flower Colors

pink
lavender

Foliage Colors

green

Fall Foliage Colors

no change

Bloom Information

Bloom Period

~6 weeks
J
F
M
A
M
J
J
A
S
O
N
D
Summer
Flowers from June through September. Individual flower heads bloom for 5–7 days. Flowering progresses from the terminal clusters downward over 4–6 weeks. In the Pacific Northwest, peak flowering occurs in July. Female plants produce pappus-bearing seeds that disperse by wind over distances of 0.5 mile (800 m) or more. Seeds mature 10–14 days after pollination. Pollinated by bees and butterflies.

Detailed Descriptions

Flower Description

Pink to lavender

Foliage Description

Dark green above, lighter beneath; oblong to lance-shaped with irregularly lobed, spiny-toothed margins; smooth to slightly hairy

Growing Conditions

Sun Requirements

Full Sun
Partial Shade
Requires 6-12 hours of direct sunlight daily
• Full Sun: 6+ hours of direct sunlight
• Partial Shade: 3-6 hours of direct sunlight
• Full Shade: Less than 3 hours of direct sunlight

Soil Requirements

pH Range5.5 - 8.0(Neutral)
357912
Soil Types
loamclaysandsilt
Drainage
average

Water & Climate

Water Needs

Medium

Frost Tolerance

hardy

Time to Maturity

1-2 years

Drought Tolerance

Drought tolerant when established

Care & Maintenance

Care Guide

Classified as a federal noxious weed in the United States and listed in 43 states and all Canadian provinces; management requires persistent, multi-year efforts. The extensive lateral root system stores large carbohydrate reserves that support regrowth after defoliation. Cutting or mowing at the early bud stage, repeated every 3–4 weeks throughout the growing season for 3–5 years, gradually depletes root reserves. A single missed mowing cycle allows root reserve recovery. Hand-pulling removes stems but not the deep root system and may stimulate additional adventitious shoots. Tilling fragments roots and can increase stem density in the following season. Root carbohydrate reserves are lowest at the early bud stage in midsummer; defoliation at this timing causes maximum root depletion. Biological control agents including the stem-mining weevil Ceutorhynchus litura and the gall fly Urophora cardui have been released in North America.

Pruning

No pruning applicable. Management involves cutting at the early bud stage before flowers open, repeated every 3–4 weeks to prevent root reserve recovery. Cutting below the lowest branch at 2–4 inches (5–10 cm) above ground is more depleting to roots than mowing at higher levels. All cut material with developed flower heads should be removed from the site, as heads may produce viable seed after cutting.

Maintenance Level

high

⚠️ Toxicity Warning

Non-toxic