Common Name: Kalm's St. John's wort
Type: Broadleaf evergreen
Native Range: United States and Canada (Great Lakes region)
Zone: 4 to 7
Height: 2.00 to 3.00 feet
Spread: 2.00 to 3.00 feet
Bloom Time: July to August
Bloom Description: yellow
Sun: Full sun to part shade
Suggested Use: Hedge
Other: Winter Interest
Easily grown in average, medium moisture, well-drained soils in full sun to part shade. Prefers moist, rich, sandy loams. Tolerates poor soils. Established plants tolerate some drought. Prune if needed after bloom in late summer.
Hypericum kalmianum, commonly called Kalm St. Johns wort, is a small, dense, evergreen shrub or subshrub with upright branching that typically grows in a dense mound to 2-3’ tall. It is native to the Great Lakes region of the U.S. where it typically occurs in rocky to sandy soils, ranging from relatively dry open woods to moist lakeshore areas. Narrow, linear-oblong, stalkless, bluish-green leaves (to 2” long) in pairs on distinctive 4-angled stems are evergreen but some may drop in winter. Five-petaled, golden yellow flowers (1.5-inch diameter) in 3- to 7-flowered cymes bloom in mid to late summer (July-August). Each flower has five styles and a distinctive center boss of yellow stamens. Flowers give way to beaked, oval, brown seed capsules that mature in fall and often persist on the shrub until spring. Leaves are dotted with tiny glands.
Genus name comes from the Greek words hyper meaning above and eikon meaning picture in reference to the practice of hanging flowers from this genus above images, pictures or windows.
Specific epithet honors Peter Kalm, a student of Linnaeus, who reportedly discovered this plant in the wild in North America in the mid-1700s.
No serious insect or disease problems.
Low hedge, border or rock garden. Wood margins, rocky slopes, wild gardens, naturalized areas or pond peripheries.