Bull thistle (Cirsium vulgare)

Synonyms: Carduus vulgaris, Cirsium lanceolatum, Carduus lanceolatus

Common Names: Common thistle, spear thistle, fuller's thistle

Description:

Bull thistle (Cirsium vulgare) is a tall, very spiny weed from Europe, western Asia, and northern Africa that has spread across North America along roads, pastures, fields, and other disturbed ground [1][2]. It is a biennial ? it spends one year as a low spiny rosette, then shoots up a flowering stalk the next year [1]. MISIN tracks it because it forms spiny patches that crowd out native plants, lower the quality of pasture and wildlife forage, and pump out huge numbers of wind-blown seeds [2].

Habit:

Bull thistle changes a lot between its two years. In its first year it is a flat rosette of deeply lobed, very spiny leaves [1]. In its second year it sends up a branching, spiny stalk 2 to 5 feet tall (sometimes taller) topped with large reddish-purple to pink flower heads about 1.5 to 2 inches across, blooming from early summer into fall [1][2]. Two features help confirm it: the stems have spiny "wings" running down them, and the upper surface of the leaves is rough and bristly with stiff hairs while the underside is woolly and white [1][2].

It is easiest to find and remove in spring and early summer ? dig the rosettes before they bolt, or cut second-year plants before the purple heads open and set seed [1]. Several beneficial native thistles look similar, so check the leaf surface and stem before removing anything (see Similar Species) [2].

At-a-glance cues:

1. Stems have spiny "wings" running down them [1]
2. Leaf upper surface is rough and bristly with stiff hairs; underside is woolly and white [1][2]
3. Large reddish-purple to pink flower heads (1.5?2 in) with stiff, yellow-tipped spiny bracts, summer into fall [1][2]
4. First-year plants are a flat, very spiny rosette [1]

Leaves:

1. Arrangement: a basal rosette in year one; alternate along the stem in year two [1]
2. Shape: deeply lobed (pinnatifid); rosette leaves can be 8?24 inches long [2]
3. Margin: very spiny, with stiff prickles along the edges and lobe tips [1]
4. Surface: upper side rough and bristly with stiff hairs (prickly to the touch); underside woolly and white [1][2]

Stems:

1. Habit: erect, branched, spiny biennial, commonly 2?5 feet (up to about 6.5 ft) tall in the second year [1][2]
2. Wings: stems have spiny "wings" running down them ? a key feature [1]
3. Surface: cottony-hairy and prickly [1]
4. Root: a stout, fleshy taproot ? the plant does not spread from roots [1]

Flowers:

1. Color: reddish-purple to pink [1]
2. Shape: large, brush-like composite heads about 1.5?2 inches across, with a spiny base whose bracts are stiff and tipped with yellow spines [1][2]
3. Arrangement: single or in groups of 2?3 at the tips of branches [2]
4. Bloom time: early summer into fall (about June to October) [1]

Fruit and seeds:

1. Fruit: small dry seeds (achenes) about 3?4 mm long [2]
2. Plume: each seed carries a feathery white plume (pappus) that detaches easily and carries it on the wind [1][2]
3. Output: roughly 100?300 seeds per flower head, and a large plant can carry hundreds of heads ? a single plant can make many thousands of seeds [2]
4. Seed bank: seeds can stay alive in the soil for up to about 10 years [2]

Habitat:

Bull thistle is a plant of open, disturbed, sunny ground. It is common in pastures, overgrazed rangeland, hayfields, roadsides, ditches, fence lines, recently burned or logged forest, and other disturbed areas, and it can move into meadows and the edges of natural areas [2]. It needs open ground and sun to get started, so it thrives where soil has been disturbed or grazed hard [2].

The plant is native to Europe, western Asia, and northern Africa [2]. It has naturalized across most of North America and is now a widespread weed of pastures and disturbed land [2][3]. It is not native anywhere on this continent [3].

Reproduction:

Bull thistle spreads only by seed ? it has no creeping roots ? and those seeds travel on the wind [1][2]. Each plant produces a huge number of seeds, each with a fluffy plume that can drift well beyond the parent, so new plants appear on bare or disturbed ground far from the original patch [2]. Seeds can also hitch a ride on clothing, animals, vehicles, and contaminated hay [2].

As a biennial, it germinates in spring, grows a rosette its first year, overwinters, then bolts and flowers in its second year before dying [1]. Because everything depends on setting seed, the key to control is timing: dig or cut the plant before the flower heads open and set seed, and remember the soil seed bank can stay alive for up to about 10 years, so a site needs watching for several seasons (see Management) [2].

Impact and Damage:

For homeowners and landowners, bull thistle is a sharp, painful nuisance that takes over pastures, paddocks, and disturbed corners. Its dense, spiny stands are avoided by grazing animals, which lowers the usable forage in a pasture and lets the thistle spread as animals eat around it [2]. The stiff spines also make infested ground unpleasant to walk or work in [2].

For natural areas, bull thistle invades disturbed openings, burned areas, and meadow edges, where it can form dense patches that crowd out native plants and reduce plant diversity and wildlife forage [2]. It is mainly a colonizer of disturbed ground rather than a deep-forest invader, but its enormous seed output and long-lived seed bank let it persist and spread once it gets a foothold [2]. Note that several native thistles are valuable to pollinators and birds, so correct identification matters before any removal [2].

Similar species:

Several thistles look alike, and some are beneficial natives ? check the stem and leaf surface before removing any thistle.

Canada thistle (Cirsium arvense) is another invasive thistle, but it is a perennial that spreads by creeping roots, has much smaller flower heads (about ? inch), smoother leaves, and stems without bull thistle's spiny wings.

Native thistles (Cirsium spp.) such as field and swamp thistle are valuable to pollinators and birds; they typically have smoother (not bristly) upper leaf surfaces and stems that lack the continuous spiny wings of bull thistle, so confirm before removing.

Nodding (musk) thistle (Carduus nutans) is a non-native thistle with large, often nodding purple heads on broad, smooth (hairless) bracts, unlike bull thistle's upright heads with stiff, yellow-tipped spiny bracts.

Monitoring and rapid response:

Signs to watch for:

1. First-year plants: flat, very spiny rosettes of deeply lobed leaves [1]
2. Second-year plants: spiny-winged stems 2?5 feet tall with large reddish-purple heads and yellow-tipped spiny bracts, summer into fall [1][2]
3. Bristly-topped, white-woolly-bottomed leaves ? and new patches on bare, grazed, or burned ground [2]

What you can do:

1. Dig or cut the taproot a couple of inches below the crown with a spade or hoe before the plant flowers ? best in spring or early summer; because bull thistle spreads only by seed and won't regrow from roots, severing the taproot kills the plant [1][2].
2. Cut and bag the flower heads before the seeds ripen, since cut heads can still mature seed ? put them in the trash, not the compost, to stop wind-blown spread [2].
3. Wear gloves and long sleeves for the spines, and confirm the plant is bull thistle (not a beneficial native thistle) before removing it [2].
4. Natural area crews can mow or cut to prevent flowering, dig taproots across a site before seed set, prioritize plants about to bloom, and keep monitoring for several years because of the long-lived seed bank [2].
5. Report sightings (below) to help track where this thistle is spreading [2].

When to call a professional:

1. Large, dense, or widespread infestations ? especially across pasture or rangeland ? where hand digging can't keep up; a land manager or licensed applicator can plan a larger-scale approach [2].
2. For chemical control options, contact a licensed applicator or your local cooperative extension office.

Report sightings to MISIN. Help track this species' spread by submitting observations through the MISIN web site or the MISIN mobile app (Android, iOS, Windows, and macOS). Photos at multiple angles paired with a precise GPS location are the most valuable data for confirming new occurrences and triggering rapid-response review.

Credits:

1. Penn State Extension. Bull Thistle Identification and Management. extension.psu.edu
2. U.S. Forest Service, Fire Effects Information System (FEIS). Cirsium vulgare. fs.usda.gov
3. USDA NRCS PLANTS Database. Cirsium vulgare (Savi) Ten. (bull thistle). plants.usda.gov

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