Bloomipedia
Common St. John's wort (Hypericum perforatum)
Photo: Laura J. Costello via iNaturalist · CC BY 4.0 · resized

Flower profile

Common St. John's wort

Hypericum perforatum

Introduced in the lower 48

Common St. John's wort is a wildflower that USDA PLANTS lists as introduced in the lower 48 states. It's on our flower lists for 5 states, and across the U.S. it's most often seen in bloom in June–September.

45states
5of our state lists
22,337U.S. sightings*

*iNaturalist research-grade observations, as of October 17, 2026.

On our lists for: Massachusetts, Michigan, New Hampshire, Rhode Island, Washington

🚫
Regulated invasive plant in Washington. It's on that state' official invasive plant list (Washington: Class C noxious weed). Please don't plant or share it there. WAC 16-750

Quick look

Hypericum perforatum, commonly known as St. John's wort, is a flowering plant in the family Hypericaceae. It is a hairless, perennial herb with woody roots, yellow flowers marked by black glands, and leaves that appear perforated due to translucent glands, producing thousands of seeds per plant.

  • It belongs to the Hypericaceae family. iNaturalist
  • USDA PLANTS describes it as an herb (forb) with a perennial life cycle. USDA PLANTS
  • USDA PLANTS lists it as introduced in the lower 48 states and records it in 45 states. USDA PLANTS
  • NatureServe lists it as not native to Washington, Michigan, Massachusetts, New Hampshire and Rhode Island. NatureServe
  • In Washington, most iNaturalist sightings of it in flower come in June–September. iNaturalist
  • In Michigan, most iNaturalist sightings of it in flower come in June–September. iNaturalist
  • iNaturalist has 2,985 research-grade sightings of it in Washington, ranking #58 among the 110 flowers on our Washington list. iNaturalist
  • iNaturalist has 1,627 research-grade sightings of it in Michigan, ranking #101 among the 111 flowers on our Michigan list. iNaturalist
  • iNaturalist has 1,459 research-grade sightings of it in Massachusetts, ranking #99 among the 110 flowers on our Massachusetts list. iNaturalist

State flower gift ideas

This one is a regulated invasive plant, so here are state flower gifts instead.

🌱 Sample spot. Handmade gift picks from independent shops will appear here once our shop partnership is approved. These cards are placeholders, not real products.

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    State flower print

    Gift pick coming soon

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    Birth-flower necklace

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    Wildflower seed favors

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    Botanical tea towel

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    Pressed-flower frame

    Gift pick coming soon

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    Flower-garden mug

    Gift pick coming soon

When does it bloom?

Flowering records by month across the U.S. (iNaturalist research-grade observations marked “Flowering”) (3,002 records)
Bloom time in each of our 5 states
StateTypePeak bloomSightings*
WashingtonIntroducedJune–September2,985
MichiganIntroducedJune–September1,627
MassachusettsIntroducedJune–August1,459
New HampshireIntroducedJune–August445
Rhode IslandIntroducedJune–July222

Conservation status

Federal (U.S. ESA)
Not listed No U.S. Endangered Species Act listing in the USFWS ECOS database. USFWS ECOS
NatureServe global
GNR Not yet ranked worldwide. NatureServe
Washington
No list Washington has no state law listing endangered or threatened plants (the Washington Natural Heritage Program's rare plant list isn't regulatory), so we show NatureServe's Washington ranks instead. NatureServe: SNA, not applicable (usually because it isn't native there) in Washington.
Michigan
Not listed Not on Michigan endangered and threatened plants (Mich. Admin. Code R 299.1028, eff. March 20, 2023). NatureServe: SNA, not applicable (usually because it isn't native there) in Michigan. R 299.1028
Massachusetts
Not listed Not on Massachusetts Endangered Species Act list (321 CMR 10.90). NatureServe: SNA, not applicable (usually because it isn't native there) in Massachusetts. MESA list
New Hampshire
Not listed Not on New Hampshire Official Rare Plants List (Ncr 312, eff. Jan 1, 2020). NatureServe: SNA, not applicable (usually because it isn't native there) in New Hampshire. NH Ncr 312
Rhode Island
Not listed Not on Rhode Island Rare Plants 2016 (RI Natural History Survey, from the RI Wildlife Action Plan; informational, Rhode Island has no state plant-protection listing law). NatureServe: SNA, not applicable (usually because it isn't native there) in Rhode Island. RI rare plants 2016
Rare elsewhere
No other U.S. state ranks it S1, S2, SH or SX.

Checked October 17, 2026. Rankings and lists can change, so follow the links for the latest.

Can you eat it?

For peopleCaution: partly edible, partly poisonous

NC State Extension lists it as poisonous to humans (severity: medium). Poisonous parts: leaves, sap/juice. Symptoms they list: “Skin contact with the sap, or ingestion of the plant, can cause photosensitivity in some people. Common side-effects are gastointestinal disturbances, allergic reactions and fatigue, ulcerative and exudative dermatitis.” They also note: “Ingestion of St John's wort can reduce the effectiveness of prescription medicine.” NC State Extension

For petsToxic to dogs, cats and horses

ASPCA's entry “Klamath Weed” (Hypericum perforatum) lists it as toxic to dogs, cats and horses. ASPCA

🌿 Never eat a wild plant unless you're certain of its ID; this isn't medical advice. Worried about a person? Call Poison Control at 1-800-222-1222. Worried about a pet? Call your vet.

Where does it grow?

USDA PLANTS records common St. John's wort in 45 states plus Washington, D.C.

recorded by USDA PLANTS on our state lists not recorded

See the full list of states

Arkansas, California, Colorado, Connecticut, Delaware, Georgia, Hawaii, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, Maryland, Massachusetts, Michigan, Minnesota, Mississippi, Missouri, Montana, Nebraska, Nevada, New Hampshire, New Jersey, New Mexico, New York, North Carolina, North Dakota, Ohio, Oklahoma, Oregon, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Texas, Vermont, Virginia, Washington, West Virginia, Wisconsin, Wyoming; District of Columbia.

Washington counties with USDA records: Adams, Asotin, Benton, Chelan, Clallam, Clark, Columbia, Cowlitz, Douglas, Ferry, Franklin, Garfield, Grant, Grays Harbor, Island, King, Kitsap, Kittitas, Klickitat, Lewis, Lincoln, Okanogan, Pacific, Pend Oreille, Pierce, San Juan, Skagit, Skamania, Snohomish, Spokane, Stevens, Thurston, Wahkiakum, Walla Walla, Whatcom, Whitman, Yakima.

Michigan counties with USDA records: Alcona, Alger, Allegan, Alpena, Antrim, Arenac, Baraga, Barry, Benzie, Berrien, Branch, Calhoun, Cass, Charlevoix, Cheboygan, Chippewa, Clare, Clinton, Crawford, Delta, Dickinson, Emmet, Genesee, Gladwin, Gogebic, Grand Traverse, Houghton, Huron, Ingham, Ionia, Iron, Isabella, Jackson, Kalamazoo, Kalkaska, Kent, Keweenaw, Lake, Lapeer, Leelanau, Lenawee, Livingston, Luce, Mackinac, Macomb, Manistee, Marquette, Mason, Mecosta, Menominee, Missaukee, Monroe, Montcalm, Montmorency, Muskegon, Newaygo, Oakland, Oceana, Ogemaw, Oscoda, Otsego, Ottawa, Presque Isle, Roscommon, Saginaw, Sanilac, Schoolcraft, Shiawassee, St. Clair, St. Joseph, Van Buren, Washtenaw, Wayne.

Massachusetts counties with USDA records: Barnstable, Berkshire, Bristol, Dukes, Essex, Franklin, Hampden, Hampshire, Middlesex, Nantucket, Norfolk, Plymouth, Suffolk, Worcester.

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Sources