Great St. Johnswort
Hypericum ascyron
Last reviewed: July 2026
Hypericum ascyron (Great St. Johnswort) is a native perennial forb blooming June through August with bright yellow flowers. Found across northeastern and midwestern states, it attracts bees, butterflies, and beetles.
The USDA PLANTS Database (opens in new tab) does not flag Great St. Johnswort as toxic to livestock.
Light
full sun
Water
medium
Size
24"–48" H × 12"–24" W
Bloom
Jun, Jul, Aug
Native to
CT, IA, IL, IN and 13 more states
Pollinators
bees, butterflies, beetles
Great St. Johnswort is a tall native perennial that produces bright yellow flowers with prominent stamens from June through August. This robust plant forms upright clumps and thrives in full sun with moderate water needs.
Growing Great St. Johnswort
Grow Great St. Johnswort in full sun and medium water. Mature plants reach 24 to 48 inches tall and spread 12 to 24 inches wide. Expect low maintenance to keep it looking intentional in a front yard.
In an HOA neighborhood
Great St. Johnswort is an HOA-friendly choice. Maintenance level: low. Tidiness: 3 out of 5.
Works well in: mid zone, foundation.
- Tall height may appear unstructured in formal settings
- Winter dormancy leaves bare stems
Wildlife value
The cheerful yellow blooms attract bees, butterflies, and beetles throughout the summer months. This native plant provides important nectar resources during peak growing season.
Common questions
- When does Great St. Johnswort bloom?
- Hypericum ascyron blooms from June through August, producing bright yellow flowers that attract various pollinators.
- What pollinators visit Great St. Johnswort?
- Great St. Johnswort attracts bees, butterflies, and beetles with its summer flowers.
- Where is Hypericum ascyron native?
- Great St. Johnswort is native to northeastern and midwestern states including Connecticut, Iowa, Illinois, Indiana, Kansas, Massachusetts, Maryland, Maine, Michigan, Minnesota, Missouri, New Hampshire, New York, Ohio, Pennsylvania, Vermont, and Wisconsin.
- What growing conditions does Great St. Johnswort prefer?
- This native forb thrives in full sun to partial sun with medium to moist soil conditions.
- Is Great St. Johnswort toxic to livestock?
- The USDA PLANTS Database does not flag Great St. Johnswort as toxic to livestock.
- Is Great St. Johnswort HOA-friendly?
- Great St. Johnswort is generally an HOA-friendly choice in the right placement, with low maintenance.
Native range data from the USDA PLANTS Database and regional native plant society lists. Pollinator and host plant associations compiled from GBIF, iNaturalist, and published ecological literature.
Ready to grow Great St. Johnswort? Add it to your garden in Pollinator Patch to track it and get season-by-season care guidance.
Not sure where to start? Take the 2-minute yard quiz