Hypericum Species, Perforate St. John's Wort, Common St. Johnswort, Klamath Weed

Hypericum perforatum

Family: Hypericaceae (hy-PER-ee-KAY-see-ee) (Info)
Genus: Hypericum (hy-PER-ee-kum) (Info)
Species: perforatum (per-for-AY-tum) (Info)



Water Requirements:

Average Water Needs; Water regularly; do not overwater

Sun Exposure:

Sun to Partial Shade



Foliage Color:

Unknown - Tell us


12-18 in. (30-45 cm)

18-24 in. (45-60 cm)


18-24 in. (45-60 cm)


USDA Zone 4a: to -34.4 C (-30 F)

USDA Zone 4b: to -31.6 C (-25 F)

USDA Zone 5a: to -28.8 C (-20 F)

USDA Zone 5b: to -26.1 C (-15 F)

USDA Zone 6a: to -23.3 C (-10 F)

USDA Zone 6b: to -20.5 C (-5 F)

USDA Zone 7a: to -17.7 C (0 F)

USDA Zone 7b: to -14.9 C (5 F)

USDA Zone 8a: to -12.2 C (10 F)

USDA Zone 8b: to -9.4 C (15 F)

Where to Grow:

Grow outdoors year-round in hardiness zone



Bloom Color:

Bright Yellow

Bloom Characteristics:

Unknown - Tell us

Bloom Size:

Unknown - Tell us

Bloom Time:

Mid Summer

Other details:

May be a noxious weed or invasive

Soil pH requirements:

5.1 to 5.5 (strongly acidic)

5.6 to 6.0 (acidic)

6.1 to 6.5 (mildly acidic)

6.6 to 7.5 (neutral)

Patent Information:


Propagation Methods:

From softwood cuttings

From seed; direct sow outdoors in fall

From seed; winter sow in vented containers, coldframe or unheated greenhouse

From seed; sow indoors before last frost

Seed Collecting:

Allow pods to dry on plant; break open to collect seeds


This plant has been said to grow in the following regions:

Birmingham, Alabama

Pottsville, Arkansas

Ceres, California

Rehoboth Beach, Delaware

Woodstock, Georgia

Centerville, Iowa

Erie, Michigan

Saint Helen, Michigan

Cole Camp, Missouri

Saint Louis, Missouri

Euclid, Ohio

Salem, Oregon

Coatesville, Pennsylvania

Downingtown, Pennsylvania

Feasterville Trevose, Pennsylvania

Millersburg, Pennsylvania

Norristown, Pennsylvania

Wakefield, Rhode Island

Columbia, South Carolina

Hendersonville, Tennessee

Wytheville, Virginia

show all

Gardeners' Notes:


On Jul 8, 2016, coriaceous from ROSLINDALE, MA wrote:

This herbaceous perennial spreads aggressively both by rhizomes and by self-sowing. Fairly weedy here in Massachusetts.

Native to Europe and Asia (but not N. America), and naturalized widely in temperate parts of the world, including 47 of the lower 48 states. 10 states in the west and north have declared it invasive. http://bonap.net/MapGallery/County/Hypericum perforatum.png

8 states and more than 20 countries have declared it a noxious weed. It is toxic to livestock, and renders meadows unsuitable for grazing.


On Jul 8, 2016, Rickwebb from Downingtown, PA wrote:

I see this Eurasian perennial occasionally in different spots in fields and roadsides in eastern North America as a wildflower. I am not aware of any nurseries selling it.


On Aug 24, 2013, pookha from edmonton,
Canada wrote:

Classified as a prohibited noxious weed by Govt. Alberta
Please check your province/state


On Nov 29, 2006, Rotegard from Minneapolis, MN wrote:

Our St. John's Wort is the hardiest ground cover herb in the Lasalle community garden (Minneapolis 55403) its yellow flowers bloom most of the growing season and are good for bees. Our patch is in full//partial sun and has to be trimmed back to keep it from overwhelming neighboring Elecampene, Rue, and Melissa. It also grows wild in the prairie habitat in the Eloise Butler Wildflower garden on the west side of the city. The flowers make a useful tincture in little (50ml) vodka bottles.


On Jul 27, 2003, PurplePansies from Deal, NJ (Zone 7a) wrote:

This plant grows wild where I am, (the Mid-Atlantic). It's not a really showy plant, not suited for a perennial or flower garden. Although it may be at home in a wild, wild-flower or medicinal/herb garden. It is pretty invasive, so don't plant near shyer plants. Can grow in dryer soil but prefers moister, grows very well in even wet soil, (it often grows here on riversides and beside lakes). Grows in sun to partial sun, partial shade. Said to be useful in treating depression, but I have no idea how to prepare the plant for this use.


On Jul 30, 2002, smiln32 from Oklahoma City, OK (Zone 7a) wrote:

Hypericin compounds found in flower petals, leave and stem tissue are said to have antidepressant effect in humans, but can cause light sensitivity.


On Aug 13, 2001, Terry from Murfreesboro, TN (Zone 7a) wrote:

Perforated St. John's Wort is found in drier conditions than other species.

A popular herb in medieval times, St. John's Wort has recently been rediscovered as an herbal anti-depressant.