Great St. Johnswort: A Towering Native Perennial for Wet Gardens
If you’re looking for a tall, cheerful native perennial that thrives in those tricky wet spots in your garden, great St. Johnswort (Hypericum ascyron) might just be your new best friend. This impressive native wildflower brings bright yellow blooms to the late summer garden when many other plants are starting to fade.
What Makes Great St. Johnswort Special?
Great St. Johnswort is a true native gem, naturally occurring across much of the northern United States and southern Canada. You’ll find this hardy perennial growing wild from Maine to Kansas, and from Ontario down to West Virginia. It’s a plant that has been quietly beautifying North American landscapes for centuries.
This isn’t your typical garden-variety perennial. Great St. Johnswort can reach an impressive 5 feet in height, making it a real statement plant in the landscape. Its bright yellow flowers appear in late summer, providing a welcome splash of color when many gardens are starting to look tired.
A Note About Rarity
Before you start planning where to plant great St. Johnswort, it’s important to know that this species has become quite rare in some areas. In New Jersey, for instance, it’s listed as S2 (imperiled) and appears on the Highlands Listed species. If you’re fortunate enough to find this plant for sale, make sure you’re purchasing from a reputable native plant nursery that uses responsibly sourced, locally appropriate genetic material.
Perfect Growing Conditions
Great St. Johnswort has some specific preferences that make it perfect for certain garden situations:
- Moisture: This plant loves consistent moisture and can handle wet feet, making it ideal for rain gardens and pond edges
- Soil: Prefers fine to medium-textured soils with medium fertility
- pH: Thrives in slightly acidic to neutral soils (pH 5.7-7.1)
- Sunlight: Needs full sun to perform its best
- Hardiness: Cold hardy to about -23°F (roughly zones 4-7)
Where to Use Great St. Johnswort in Your Landscape
This tall native is perfect for several garden situations:
- Back of borders: Its 5-foot height makes it an excellent backdrop plant
- Rain gardens: Its love of moisture makes it ideal for managing stormwater
- Wetland edges: Perfect for transitioning from upland to wetland areas
- Native plant gardens: A must-have for authentic regional plant communities
- Naturalized areas: Great for creating meadow-like landscapes
Benefits for Wildlife and Pollinators
Those cheerful yellow flowers aren’t just pretty to look at—they’re also valuable to local wildlife. The late summer blooms provide nectar when many other flowers have finished, making them especially important for bees and other pollinators trying to stock up before winter.
Growing Tips and Care
Great St. Johnswort is refreshingly low-maintenance once established, but getting it started requires a bit of patience:
- Propagation: Seeds require cold stratification, so be patient with germination
- Growth rate: Moderate grower that takes time to reach full size
- Planting: Best grown from container plants rather than direct seeding
- Spacing: Give plants plenty of room—they can spread to form nice clumps
- Maintenance: Very low maintenance once established
Is Great St. Johnswort Right for Your Garden?
Great St. Johnswort is an excellent choice if you have a wet or consistently moist area in full sun and want to grow native plants. Its tall stature and late-season blooms make it particularly valuable for adding structure and color to rain gardens and naturalized areas.
However, this might not be the plant for you if you have a small garden, prefer dry conditions, or need something that blooms earlier in the season. Its 5-foot height can be overwhelming in compact spaces, and it really doesn’t perform well in dry soils.
If you can provide the right conditions and source the plant responsibly, great St. Johnswort rewards you with years of reliable late-summer color and the satisfaction of growing a true native that supports local ecosystems. Just remember to respect its rarity status and always choose nursery-propagated plants over wild collection.
