St. John's Wort is a herbaceous, perennial, deciduous or evergreen shrub growing to 3 feet high by 2 feet wide. In nature, St. John's Wort is often found in open woods, roadsides and waste places, hedge banks and grassland, and in dry sunny places, usually on calcareous soils. Introduced from Europe, it is now found throughout the United States. St. John's Wort is in flower from May to August, and the seeds ripen from July to September. This species is usually in bloom during the summer solstice (dedicated to St. John), hence the common name. The plant is self-fertile and can rapidly spread to the point where it is potentially invasive. The root pattern is rhizomatous with underground stems sending roots and shoots along their length. A single plant may produce up to 100,000 seeds per year and seeds buried in soil may last for 10 years. St. John's Wort tolerates most soil types, including sandy, loamy, and clay soils, but prefers well-drained, moist soil. It can grow in semi-shade (light woodland) or no shade, but full sun is best for maximum blooms. It can also tolerate drought. See native alternatives to the left. Diseases, Insect Pests, and Other Plant Problems : No serious insect or disease problems. Invasive spread can displace native species.
Curated pairwise relationships between this plant and others in the library — who feeds
whom, who competes, who confuses the pests. Green reads as a good pairing, red as one to avoid.
No curated interactions recorded for this species yet.
Also noted by NC State
Related species the NC State Plant Toolbox flags for this plant — look-alikes to tell
apart, and plants that play a similar role in a planting. Ones we carry in the library are linked.
Full sun (6 or more hours of direct sunlight a day) | Partial Shade (Direct sunlight only part of the day, 2-6 hours)
Soil texture
Clay; Loam (Silt); Sand
Soil pH
Acid (<6.0); Alkaline (>8.0); Neutral (6.0-8.0)
Soil drainage
Good Drainage | Moist
NC region
Coastal; Mountains; Piedmont
Mature size
Height: 1 ft. 0 in. - 3 ft. 0 in. | Width: 0 ft. 9 in. - 2 ft. 0 in.
Growth rate
Medium
Maintenance
High
Canopy layer
4 - Herbaceous (3-15 ft)
Form & Appearance
Habit / form
Dense; Mounding; Multi-stemmed; Spreading
Texture
Medium
Foliage
Deciduous
Leaf color
Green
Leaf type
Simple
Leaf arrangement
Opposite; Whorled
Leaf shape
Oblong
Leaf margin
Entire
Leaf size
< 1 inch long, < 1 inch wide
Hairs present
No
Leaf detail
Leaves are about 1 inch long and 1/3 of an inch across. They are oblong, hairless, and sessile. The surface of these leaves is perforated by numerous translucid dots, and there are often scattered black dots along the margin of the lower surface.
Flower color
Gold/Yellow
Flower value
Long Bloom Season; Showy
Flower form
Cyme
Flower size
1-3 inches
Flower detail
Yellow petals with black dots on margins; bushy stamens. Solitary or cymose, terminal or axillary. Yellow (usually) 5-petaled (rarely 4), 5 sepals (rarely 4); stamens numerous, in bundles or in showy boss. The upper stems terminate in flat-headed clusters of several flowers. Each flower is about ¾ of an inch across. There are scattered black dots along the margins of the petals.
Bloom time
Spring; Summer
Fruit color
Brown/Copper
Fruit type
Capsule
Fruit detail
Each 3-celled seed capsule is well-rounded at the base, becoming conical at its apex. Each cell of the seed capsule contain numerous seeds, which are oblong, flattened, and black. The surface of each seed is somewhat roughened by numerous small pits, rather than smooth.
Stem color
Green
Stem detail
Contains 2 to 4 (up to 6) ridges on newer growth, smooth and rounded on older growth.
Wildlife & Ecology
Native status
Non-native
Origin
Europe, North Africa, Western Asia
Distribution
Throughout the United States and Canada
Attracts
Bees; Pollinators
Play value
Attracts Pollinators; Wildlife Food Source
Food & Medicine
Harvest time
Fall
Fruit type
Capsule
Edibility
Ingestion of St John's wort can reduce the effectiveness of prescription medicine.
Uses (ethnobotany)
Native Americans have been known to use this plant for medicinal purposes. Flowers can be used as a yellow dye plant.
Landscape Use
Landscape location
Recreational Play Area; Slope/Bank; Woodland
Landscape theme
Children's Garden; Pollinator Garden
Design feature
Barrier; Mass Planting
Garden tags
#children's garden #yellow flowers #nectar plant #pollinator plant #fantz #problem for dogs #problem for horses #problem for cats #playground plant #dye plant #wildflower #weedy #high maintenance #contact dermatitis
Problems & Resistance
Problems
Problem for Cats; Problem for Dogs; Problem for Horses
Resistant to
Deer; Drought; Poor Soil
Propagation
Division; Seed
Poison severity
Medium
Poison parts
Leaves; Sap/Juice
Poison symptoms
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.
Toxic principle
Hypericin
Contact dermatitis
Yes
Toxicity summary
Medium severity poison; parts: Leaves; Sap/Juice; contact dermatitis