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A Forager’s Year

No. 167

Bull thistle

Cirsium vulgare

common thistle, spear thistle

Roots, bulbs & tubers first-year taproot (dug from the spiny rosette, peeled and cooked)

Drawing: Britton & Brown, Illustrated Flora (1913)

Find
Common in the right habitat
Effort
Quick kitchen prep
ID risk
Careful
Origin
non-native ★★
Safety marks
  • Deadly lookalike
  • Spray risk
Uses
  • Cooked vegetable / soup

Season

  1. Jan
  2. Feb
  3. Mar
  4. Apr
  5. May
  6. Jun
  7. Jul
  8. Aug
  9. Sep
  10. Oct
  11. Nov
  12. Dec

in season peak

Picking: No park we checked allows it. Anywhere else, ask whoever owns or runs the land. See Where you may pick.

What these mean

Find

1 Everywhere · 2 Common in the right habitat · 3 Patchy · 4 Elusive. This is about how much there is, not whether you may pick it. It is based on iNaturalist sightings within 25 km (about 15 miles) of downtown DC, counted on October 3, 2026. The four rules that each plant’s “Find” reason refers to: (A) the estimate is the confirmed sightings, plus the unconfirmed ones (scaled down where the plant has lookalikes in its genus), plus the sightings marked as planted; (B) the tier by estimate: 1,500 or more is tier 1, 250–1,499 tier 2, 50–249 tier 3, under 50 tier 4; (C) tier 1, Everywhere, also needs a source saying the plant is common in lawns, sidewalks, yards or gardens, vacant lots or towns, or at least one DC street tree of it per km of sidewalk, otherwise it is tier 2; (D) if a reliable source says the plant is rare in this region, or that wild plants rarely bear the harvest, only planted sightings count. iNaturalist is a website and phone app where people post photos of the plants and animals they see. A sighting is “research grade” when other users have confirmed what it is; “needs ID” sightings are not confirmed yet, and “cultivated” ones are marked as planted.

Effort

1 Grab & eat · 2 Quick kitchen prep (under about 30 minutes) · 3 Real work (hours, or cooking needed for safety) · 4 Project (days or equipment). Scored on the simplest worthwhile use; each plant’s page says why.

ID risk

How hard it is to harvest safely. Beginner: no dangerous lookalike, and the edible part is not easily confused with a toxic part. Careful: a toxic lookalike, or toxic parts that end up in the harvest unless removed (for example elderberry stems, unripe ground cherries), or other parts of the plant rated medium-or-higher toxicity, with reliable features to separate them. Expert only: a potentially deadly lookalike that is hard to separate, or (for not-recommended harvests like pokeweed) a plant whose safe preparation can’t be guaranteed. Toxic parts that are obviously separate and thrown away anyway (pits, seeds, skins) don’t raise it; the Toxic parts mark carries that warning.

Native or not, and the invader stars

Origin is where the plant comes from: native, non-native, or mixed (the harvest covers both). The stars rate plants on invasive plant lists: ★★★ Virginia DCR “High” or Maryland prohibited invasive · ★★ Virginia “Medium” · ★ Virginia “Low” · ☆ listed only by the Maryland Invasive Species Council or the Mid-Atlantic Plant Invaders guide (advisory) · no stars: native or not listed.

Safety marks and flags

Deadly lookalike / Toxic lookalike: a cited source names a lookalike of that danger, recorded near DC (an iNaturalist sighting within 25 km, a DC street tree, or a Smithsonian listing for DC) and looking like the part you eat. Other lookalikes are still listed, marked “not recorded near DC” or as not looking like the part you eat. Deadly means a source says eating it may be fatal or calls it deadly, or NC State rates it high severity with life-threatening symptoms (sources sometimes disagree; for example Virginia creeper). Each plant’s Lookalikes list says how to tell them apart; “harmless (may be edible)” lookalikes are listed so you know a mix-up isn’t dangerous. Cook first: cooking is needed for safety (for daylilies it is a precaution, not a sourced requirement). Eat in moderation: a source says to limit quantity or frequency (for example oxalates in sorrels and dock, ginkgotoxin, safrole). Spray risk: a source says the plant is commonly treated with herbicide in parks or lawns (invasive control, lawn weeds) or, for ginkgo, sprayed to stop fruiting. Contamination: a source says the plant concentrates pollutants. Each plant’s Safety flags list gives the details and sources.

Seasons

Start, peak and end are given in thirds of a month: early, mid or late. A plant counts as in season for a month if it is in season at any point in that month. Some greens and roots have a second window, in spring or fall; their page shows each window. A season that runs across New Year is shown as one window.

What it looks like

The taproot of bull thistle in its first year, while the plant is still a flat rosette of leaves and before it sends up a flower stalk in its second year (USDA Forest Service; Ohio State). The rosette can grow to about 3 feet across (Ohio State; Maryland Department of Agriculture). Its leaves are deeply lobed, with a long, sharp spine at the tip of each lobe; the upper surface is dark green, covered with sharp hairs and prickly to the touch, and the underside is covered with soft, woolly hairs (Ohio State; Maryland Department of Agriculture). NC State says the fine, bristle-like spines on the upper leaf surface set bull thistle apart from other thistles. The root is a fleshy taproot with smaller side roots (Ohio State; USDA Forest Service); the Maryland Department of Agriculture calls it short, fleshy and thick, while the USDA Forest Service says it can reach 28 inches long. Edible Wild Food says the root is best mixed with other vegetables and is rich in inulin.

Safety

No toxicity is known for bull thistle (Ohio State), and NC State lists no poisonous parts. The plant is armed with stiff, sharp spines, so wear heavy gloves (Eat The Weeds; Foraging Texas). Eat The Weeds, a foraging site, adds that some people get contact dermatitis from thistles and that thistle root gives some people gas; no safety source confirms either. Poisonous lookalike: Mexican prickly poppy, which NC State says has thistle-like leaves and is poisonous in all parts; NC State rates it highly poisonous, with symptoms that can include fainting and coma, though it says it is toxic only if large quantities are eaten. It oozes yellow sap when cut, and its blue-green leaves have grayish-white veins (NC State; Eat The Weeds). Other plants that can be mixed up with bull thistle are not known to be poisonous: Canada, musk and plumeless thistles (Maryland Department of Agriculture; Ohio State; Government of Ontario), spotted knapweed (Plant Invaders of Mid-Atlantic Natural Areas) and burdock (Virginia Tech). Bull thistle is a designated noxious weed in Maryland: the Maryland Department of Agriculture recommends spraying the rosettes with herbicide in October and November, and again in March and April, the same months the roots are dug, and it arranges herbicide spraying along state highways; Penn State Extension lists herbicides for it in lawns and landscapes. Dig only where you know the plants have not been sprayed, away from roadsides.

Lookalikes

Safety flags

Safety marks and flags: what this means

Deadly lookalike / Toxic lookalike: a cited source names a lookalike of that danger, recorded near DC (an iNaturalist sighting within 25 km, a DC street tree, or a Smithsonian listing for DC) and looking like the part you eat. Other lookalikes are still listed, marked “not recorded near DC” or as not looking like the part you eat. Deadly means a source says eating it may be fatal or calls it deadly, or NC State rates it high severity with life-threatening symptoms (sources sometimes disagree; for example Virginia creeper). Each plant’s Lookalikes list says how to tell them apart; “harmless (may be edible)” lookalikes are listed so you know a mix-up isn’t dangerous. Cook first: cooking is needed for safety (for daylilies it is a precaution, not a sourced requirement). Eat in moderation: a source says to limit quantity or frequency (for example oxalates in sorrels and dock, ginkgotoxin, safrole). Spray risk: a source says the plant is commonly treated with herbicide in parks or lawns (invasive control, lawn weeds) or, for ginkgo, sprayed to stop fruiting. Contamination: a source says the plant concentrates pollutants. Each plant’s Safety flags list gives the details and sources.

ID risk
Careful
Why
Mexican prickly poppy has thistle-like leaves and is poisonous in all parts, which NC State rates high severity, but it oozes yellow sap when cut and its blue-green leaves have grayish-white veins (NC State; Eat The Weeds); bull thistle’s leaves are dark green, rough and prickly on top and soft and woolly underneath (Ohio State; Maryland Department of Agriculture). Canada, musk and plumeless thistles, spotted knapweed and burdock can also be mixed up with it but are not known to be poisonous (Ohio State; Maryland Department of Agriculture; Government of Ontario; Plant Invaders of Mid-Atlantic Natural Areas; Virginia Tech).
Handling hazards
Thorns (minor)
Soil risk
higher
ID risk: what this means

How hard it is to harvest safely. Beginner: no dangerous lookalike, and the edible part is not easily confused with a toxic part. Careful: a toxic lookalike, or toxic parts that end up in the harvest unless removed (for example elderberry stems, unripe ground cherries), or other parts of the plant rated medium-or-higher toxicity, with reliable features to separate them. Expert only: a potentially deadly lookalike that is hard to separate, or (for not-recommended harvests like pokeweed) a plant whose safe preparation can’t be guaranteed. Toxic parts that are obviously separate and thrown away anyway (pits, seeds, skins) don’t raise it; the Toxic parts mark carries that warning.

Handling hazards: what this means

Stings, thorns, irritating or phototoxic sap, staining hulls and spiny husks, with a severity: minor = brief discomfort; moderate = rash or blisters lasting days; serious = burns, scarring or medical care possible.

Soil risk: what this means

Based on the part you eat, following the urban-soil lead guidance on the Field safety page: higher for greens, shoots and roots; moderate for flowers; low for fruit, nuts and sap.

Field safety for every outing (poison ivy, ticks, soil, and more)

When to pick

Starts
early Oct
Peak
early Nov–late Nov
Ends
mid Apr

Dig the taproot from first-year rosettes, which have no flower stalk; Common Sense Home digs them in fall. A bull thistle makes a rosette of spiny leaves and a fleshy taproot in its first year and generally overwinters that way; in its second growing season the rosette enlarges rapidly and sends up a flowering stalk (USDA Forest Service). Ohio State says the rosettes stay green and keep growing through the winter. The Maryland Department of Agriculture says the rosette is moving nutrients to its root in late fall, October to November, and that early spring, March to April, is still before the plant bolts. Eat The Weeds notes that a first-year thistle does not have much of a root for a while. No source gives dates for the DC area, so all three boundaries are estimates.

How the dates were worked out

Every start, peak and end was re-checked in October 2026. “Sourced” means a source opened during the check states that timing for the DC or Mid-Atlantic area. “Estimated” means no source states it exactly; the reason, the evidence and the source links are under “How the dates were worked out” on each plant’s page. Peaks are often estimated, because few sources name a peak. iNaturalist evidence means research-grade sightings near DC, by month, of the plant at that stage (for example, in fruit). iNaturalist is a website and phone app where people post photos of the plants and animals they see. A sighting is “research grade” when other users have confirmed what it is; “needs ID” sightings are not confirmed yet, and “cultivated” ones are marked as planted.

Season basis: estimated: start, peak, end

Start

estimated: No source dates the start for the DC area; early October is the start of the fall dig of first-year rosettes that Common Sense Home describes, and of the late-fall rosette stage the Maryland Department of Agriculture names.

Peak

estimated: No source names a best month; November is the late fall in which the Maryland Department of Agriculture says the rosette is sending nutrients to its root, after a full first season of growth.

End

estimated: No source dates the end for the DC area; mid April closes the early-spring rosette stage before bolting that the Maryland Department of Agriculture gives as March to April (a herbicide-timing statement, used here only for when the plant is still a rosette).

Evidence

start: Common Sense Home: 'Dig roots in fall from first year plants (those with no flower stalk)'. USDA Forest Service: 'An individual bull thistle plant produces a small rosette of spiny leaves and a fleshy taproot by the end of its 1st year'. Maryland Department of Agriculture: 'during the rosette stage in late fall (October - November)'. | peak: Maryland Department of Agriculture: 'during the rosette stage in late fall (October - November) as it is actively transporting nutrients to its roots'. Common Sense Home: 'Dig roots in fall from first year plants'. | end: Maryland Department of Agriculture: 'Early spring (March - April), before bolting, is the second best time.' Ohio State: 'Bull thistle rosettes remain green and continue growing throughout the winter. The rosette is 3 feet in diameter by the second spring when it gives rise to a 5-foot-tall upright flowering stem.' USDA Forest Service: 'In its 2nd growing season the rosette typically enlarges rapidly, bolts, and produces a flowering stalk.'

Where to look

Look for flat, spiny first-year rosettes in sunny fields, pastures and disturbed open ground. It is logged most on the University of Maryland campus in College Park (picking rules not checked), in Rock Creek Park and at Lake Artemesia (no digging in either), on Georgetown University’s private campus and at the National Zoo (picking rules not checked). No listed park allows digging roots, so dig only on private land with the owner’s permission, away from roadsides and places that may be sprayed.

Habitats
lawns & sidewalk cracks, disturbed ground & waste places, old fields & meadows, woods edges, trailsides & thickets
Habitats: what this means

Listed where the plant’s own sources place it in that habitat. “Disturbed ground & waste places” means a cited source places it on disturbed areas, sites, soil or ground, on waste places or waste ground, on construction or abandoned building sites (old home sites count), on rubble or in strip mines. When the source gives examples of the disturbed places, at least one example must be of that kind. Examples that do not count: natural or forestry disturbance (treefall gaps, fire, windthrow, flood scour, old riverbanks and creeks, clear-cuts); roadsides, railroads and rights-of-way; and abandoned fields, pastures and farmland, which are “Old fields & meadows”. “Vacant lots” only where a source says vacant or empty lots.

Most-logged places

None of the most-logged places allows picking.

Ask first: rules unclear or not checked

  • University of Maryland, College Park campus

    38 sightings · Legal to pick: unknown · see them on iNaturalist

    Picking rules not checked.

  • Smithsonian National Zoo

    24 sightings · Legal to pick: unknown · see them on iNaturalist

    Picking rules not checked. A federal facility, so ask before picking anything.

No picking here (3 places)
  • Rock Creek Park

    34 sightings · Legal to pick: no · see them on iNaturalist

    Look but don’t pick: Rock Creek Park’s compendium bans gathering any fruit, nut, berry, seed or greenery.

  • Lake Artemesia Natural Area

    28 sightings · Legal to pick: no · see them on iNaturalist

    Look but don’t pick: Montgomery/Prince George’s parks (M-NCPPC) ban harvesting vegetation without a permit.

  • Georgetown University campus

    26 sightings · Legal to pick: no · see them on iNaturalist

    Private property: pick only with the owner’s permission.

Most-logged places: what this means

The places with the most research-grade iNaturalist sightings within 25 km of downtown DC (re-counted in October 2026 over every named place, campuses, condominiums and private grounds included), each marked legal to pick or not. A sighting inside several named places counts once, for the smallest of them, but a sighting inside a National Park Service park never counts for a private, campus or unchecked place. iNaturalist shows where people walk and log plants, not true abundance. Private campuses, condominiums, museums, estates and utility land (Pepco’s power-line land near Sligo Creek) are marked “no” (pick only with the owner’s permission); public university campuses, city parks and other places whose picking rules were not checked (county stormwater land, the U.S. Capitol Grounds, Greenbelt’s North Woods, federal facilities such as the National Zoo) are “unknown”. A place needs at least 2 sightings, so plants with very few sightings have no places. At-risk plants (butternut, nannyberry, American chestnut, ramps, riverbank goldenrod) get places like every other plant; each page says why the plant is at risk and gives any advice its sources give. For some places, mostly Rock Creek Park, the iNaturalist map shows more sightings than the count here, because a map link cannot leave out exactly the sightings credited to another place. iNaturalist is a website and phone app where people post photos of the plants and animals they see. A sighting is “research grade” when other users have confirmed what it is; “needs ID” sightings are not confirmed yet, and “cultivated” ones are marked as planted.

Ways to use it

  • peeled and cooked as a parsnip substitute, young roots eaten as part of the meal (Foraging Texas)
  • older roots used to flavor broths and stocks, then removed before serving (Foraging Texas)
  • cooked mixed with other vegetables (Edible Wild Food)
  • in stews or stir-fries (Common Sense Home)
  • harvest in fall from first-year plants that have no flower stalk (Common Sense Home)
  • harvest with heavy gloves and a digging fork; the taproot holds tightly (Common Sense Home; Eat The Weeds)

Keeping

Keep cold and moist in the fridge for a few weeks, or dig them as needed through winter.

Use within
weeks
Keeps fresh
Weeks refrigerated in a perforated plastic bag (general guidance for root crops). University of Minnesota: root crops want cold, moist storage; perforated plastic bags in the fridge give this for a moderate time, and root cellars give it longer. Bull thistle rosettes stay green and keep growing through the winter (Ohio State), so the roots can be dug as needed.
Keeping basis
general guidance for its type

Ways to keep it

  • Store whole as researched: root cellar; canning: n/a (not shelf-canned)

    General guidance for root crops (University of Minnesota): root cellars provide cold and moist conditions; give ventilation and protect the roots from rodents.

Canning: what this means

Shelf-stable canning, three levels. Lab-tested: a lab-tested recipe from the National Center for Home Food Preservation (NCHFP) or Oregon State covers this fruit and product, or a generic recipe for its kind (the line says so, for example chokeberry). Extension recipe: a published Extension recipe (University of Alaska Fairbanks, written for Alaska species; University of Maine’s dandelion jelly), or a process that is safe only with a pH meter; follow it exactly, never improvise. No tested recipe: refrigerate or freeze, don’t can. “Hot-bottled syrup” = maple and walnut syrup, which keep when bottled hot at full syrup density. The Canning line names the exact product each source covers, for example “whole berries” or “juice”; a product not named there (such as juice from a berry with only a whole-berry recipe) has no tested recipe.

Keeping basis: what this means

“Specific to this plant” or “general guidance for its type” (for example NCHFP guidance for leafy greens applied to a wild green).

Nutrition

Not researched: in October 2026, only the calendar’s plants of the month and chicory leaves were researched.

Native or not

Origin
non-native
Native range
Europe to Siberia and the Arabian Peninsula (per NC State)
Invader credit
★★
Virginia invasive rank
Medium
Maryland invasive status
Advisory (MISC list)
Native or not, and the invader stars: what this means

Origin is where the plant comes from: native, non-native, or mixed (the harvest covers both). The stars rate plants on invasive plant lists: ★★★ Virginia DCR “High” or Maryland prohibited invasive · ★★ Virginia “Medium” · ★ Virginia “Low” · ☆ listed only by the Maryland Invasive Species Council or the Mid-Atlantic Plant Invaders guide (advisory) · no stars: native or not listed.

Virginia DCR, Virginia Invasive Plant Species List (effective September 2024), verbatim: "Under the DCR Invasive Species Assessment Protocol, approved by the Virginia Invasive Species Working Group, January 2024, species were ranked as exhibiting high, medium or low levels of invasiveness based on their threat to natural communities and native species. Invasiveness rank is higher for species that: • Alter ecosystem processes, such as succession, hydrology or fire regime. • Are capable of invading undisturbed natural communities. • Cause substantial impacts on rare or vulnerable species or natural communities or high-quality examples of more common communities. • Are found widely distributed and generally abundant where present. • Disperse readily to new areas. • Are difficult to control." The list also states: "The list is for educational purposes only and has no regulatory authority."

Maryland Department of Agriculture, Maryland Prohibited Invasive Plant Law and Regulations page, verbatim: "Plants on the Maryland Prohibited Invasive Plant List may not be added to stock after the effective date and should not be sold after their phase-out period ends."

No official DC invasive plant list was found.

How the ratings were set

Find
Common in the right habitat Estimate 1,045 = 957 research-grade iNaturalist sightings within 25 km + 180 needs-ID sightings counted at 46% (957 of the 2,086 research-grade Cirsium sightings here are bull thistle) + 5 'cultivated' (planted) sightings (rule A); that is tier 2 by count (rule B). Final tier 2.
Effort
Quick kitchen prep Wearing heavy gloves, dig the first-year taproot out from under the spiny rosette with a digging fork (it holds tightly), then peel it and cook it like a parsnip.
Find: what this means

1 Everywhere · 2 Common in the right habitat · 3 Patchy · 4 Elusive. This is about how much there is, not whether you may pick it. It is based on iNaturalist sightings within 25 km (about 15 miles) of downtown DC, counted on October 3, 2026. The four rules that each plant’s “Find” reason refers to: (A) the estimate is the confirmed sightings, plus the unconfirmed ones (scaled down where the plant has lookalikes in its genus), plus the sightings marked as planted; (B) the tier by estimate: 1,500 or more is tier 1, 250–1,499 tier 2, 50–249 tier 3, under 50 tier 4; (C) tier 1, Everywhere, also needs a source saying the plant is common in lawns, sidewalks, yards or gardens, vacant lots or towns, or at least one DC street tree of it per km of sidewalk, otherwise it is tier 2; (D) if a reliable source says the plant is rare in this region, or that wild plants rarely bear the harvest, only planted sightings count. iNaturalist is a website and phone app where people post photos of the plants and animals they see. A sighting is “research grade” when other users have confirmed what it is; “needs ID” sightings are not confirmed yet, and “cultivated” ones are marked as planted.

Effort: what this means

1 Grab & eat · 2 Quick kitchen prep (under about 30 minutes) · 3 Real work (hours, or cooking needed for safety) · 4 Project (days or equipment). Scored on the simplest worthwhile use; each plant’s page says why.

Sources

27 sources, each linked to the original.

  1. Rock Creek Park Superintendent’s Compendium National Park ServiceBacks up: picking rules
  2. 36 CFR 2.1 - Preservation of natural, cultural and archeological resources Legal Information Institute, Cornell Law School (text of federal regulation)Backs up: picking rules
  3. Virginia Invasive Plant Species List (effective date: September 2024) Virginia Department of Conservation and Recreation, Division of Natural HeritageBacks up: picking rules, native or invasive status
  4. Non-Native Invasive Terrestrial Plant Species in the State of Maryland (updates approved through the April 18, 2024 MISC meeting) Maryland Invasive Species CouncilBacks up: picking rules, native or invasive status
  5. Cirsium vulgare (Bull Thistle, Common Thistle) NC State Extension Gardener Plant ToolboxBacks up: description, habitat, safety, native or invasive status
  6. Cirsium vulgare, Fire Effects Information System (Zouhar, 2002) USDA Forest Service, Rocky Mountain Research Station, Fire Sciences LaboratoryBacks up: description, habitat, season
  7. Bull Thistle (Cirsium vulgare), Ohio Perennial and Biennial Weed Guide Ohio State University, College of Food, Agricultural, and Environmental SciencesBacks up: description, habitat, season, safety, effort & ID risk, keeping
  8. Bull Thistle Identification & Management Maryland Department of AgricultureBacks up: description, season, safety, picking rules, effort & ID risk
  9. Bull Thistle Edible Wild FoodBacks up: description, uses, habitat
  10. iNaturalist research-grade observations of Cirsium vulgare within 25 km of downtown DC iNaturalistBacks up: findability
  11. Cirsium vulgare (Savi) Ten. (Bull Thistle) (Digital Atlas of the Virginia Flora) Virginia Botanical Associates (Digital Atlas of the Virginia Flora)Backs up: habitat
  12. Annotated Checklist of the Vascular Plants of the Washington-Baltimore Area, Part I (Shetler & Orli, 2000) Smithsonian Institution, National Museum of Natural History, Department of BotanyBacks up: habitat
  13. USDA PLANTS Database: Cirsium vulgare (CIVU), native status USDA NRCSBacks up: native or invasive status
  14. Maryland Prohibited Invasive Plant Law and Regulations (Maryland Prohibited Invasive Plant List, updated January 2026; additions effective July 15, 2026; 'Next Plants To Be Assessed' 2026-2027) Maryland Department of Agriculture, Plant Protection & Weed ManagementBacks up: native or invasive status
  15. Invasive Plants in the District DC Department of Energy & EnvironmentBacks up: native or invasive status
  16. Noxious Weed Control Maryland Department of AgricultureBacks up: safety, picking rules, native or invasive status, safety details
  17. Bull Thistle Identification and Management Penn State ExtensionBacks up: safety, effort & ID risk, safety details
  18. Argemone mexicana (Mexican Prickly Poppy) NC State Extension Gardener Plant ToolboxBacks up: safety, effort & ID risk, safety details
  19. Weed identification guide for Ontario crops: Bull thistle Government of Ontario (OMAFA)Backs up: safety, effort & ID risk, safety details
  20. Common burdock (Arctium minus) Weed Profile Virginia Tech Weed Identification GuideBacks up: safety, effort & ID risk, safety details
  21. Plant Invaders of Mid-Atlantic Natural Areas, Field Guide (Swearingen & Fulton, 2022): Spotted knapweed Mid-Atlantic Invasive Plant Council / Passiflora Press (hosted by Bugwood/Mid-Atlantic Invaders Tool)Backs up: safety, native or invasive status, effort & ID risk, safety details
  22. Arctium minus (Common Burdock) NC State Extension Gardener Plant ToolboxBacks up: safety, safety details
  23. iNaturalist research-grade observations of Cirsium vulgare within 25 km of Washington, DC, by month (all observations) iNaturalistBacks up: season
  24. Thistle: It’s That Spine of Year (Green Deane) Eat The WeedsBacks up: season, uses, safety, effort & ID risk
  25. Canada and Bull Thistle: Edible from Bud to Root (Laurie Neverman) Common Sense HomeBacks up: season, uses, effort & ID risk
  26. Harvesting and storing home garden vegetables University of Minnesota ExtensionBacks up: storage, keeping
  27. Thistle, Bull (Mark Vorderbruggen) Foraging TexasBacks up: uses, safety, effort & ID risk