Hypericum kalmianum
Overview
Uses: Native gardens, pollinator gardens, rock gardens, and dry, sunny borders.
Benefits: A small native shrub from the Great Lakes region with narrow blue-green leaves and bright yellow, puffy-centered flowers in midsummer that bees love. Handles dry, sandy, or rocky soil and cold winters, and deer leave it alone. Peeling tan bark adds winter interest.
USDA Hardiness Zones: 4–7
Sun: Full Sun to Partial Shade
Life Cycle: Deciduous Shrub
Growth Habit: Mounding, Rounded — dense and bushy.
Bloom Color: Yellow
Foliage Color: Blue-Green
Mature Height: 2–3 feet
Mature Width: 2–3 feet
Bloom Season: Summer
Growth Rate: Moderate
Summary
Sunny yellow flowers on a small native shrub that thrives where the soil is thin.
Kalm’s St. Johnswort grows wild on the sandy shores, dunes, and rocky ground of the Great Lakes region, and it brings that toughness into the garden. It forms a dense, rounded mound about two to three feet tall and wide, covered in narrow blue-green leaves that stay clean and fresh through summer.
In midsummer the plant fills with bright yellow flowers, each with a puffy center of long stamens. They open over several weeks in July and August, a time when most spring-flowering shrubs have gone quiet. Bees, especially bumblebees, work the flowers heavily for their abundant pollen.
After the leaves drop, the stems show peeling, tan bark that gives the plant texture through winter. Add its tolerance for dry, sandy, or rocky ground and for cold winters, and it becomes a natural fit for rock gardens, dry slopes, and native plantings.
Care
Kalm’s St. Johnswort Care
Plant in full sun for the most flowers and the densest habit. It tolerates partial shade, though it blooms less and grows a little more open there.
Good drainage matters more than rich soil. Sandy, gravelly, or rocky soils suit it well, and it adapts to average garden soil as long as water does not sit around the roots.
Water regularly through the first growing season while roots establish. Once settled, it handles dry spells well and rarely needs watering outside of extended drought.
Feeding is seldom necessary, since it grows naturally in lean soil. If growth looks weak, a light application of a slow release fertilizer in early spring is enough.
It flowers on new growth, so do any pruning in late winter or early spring. Cut back by up to a third to keep the mound dense, and remove a few of the oldest stems at the base every few years to renew the plant.
Size
What Size is the Kalm’s St. Johnswort for Sale Online?
Our Kalm’s St. Johnswort ships in a greenhouse-grade grow pot and is appropriately sized for its container at the time of shipment. Plants ship dormant or near dormant in the off-season, so they may arrive with few or no leaves. If you have specific sizing or planting questions, please contact us.
How Large Does Kalm’s St. Johnswort Grow?
Expect about 2 to 3 feet tall and 2 to 3 feet wide at maturity, in a dense, rounded mound. Space plants about 2 to 3 feet apart for a low mass planting or informal edging.
Additional Information
Is Kalm’s St. Johnswort a native plant?
Yes. It is native to North America, growing naturally around the Great Lakes in the northern United States and southern Canada. Because it is the straight species rather than a cultivar, it offers the same habitat and pollinator value as plants in the wild. Browse more Native Plants of North America.
Is it the same as the St. John’s wort sold as an herb?
No. The herbal St. John’s wort is Hypericum perforatum, a European perennial that has naturalized widely and is treated as a weed in many areas. Kalm’s St. Johnswort is a different species: a woody shrub native to North America, grown as an ornamental landscape plant.
Will it grow in dry, sandy soil?
Yes. It grows naturally on dunes and rocky shorelines, so once established it handles dry, sandy, or gravelly ground better than most flowering shrubs. That makes it a good choice for slopes, rock gardens, and hot strips along driveways. See more Drought-Tolerant Plants.
Do deer eat Kalm’s St. Johnswort?
Deer usually pass it by, which makes it a useful flowering shrub where browsing is a problem. No plant is completely deer-proof, and hungry deer may still sample new growth in a hard winter. For more options, see our Deer-Resistant Shrubs and Evergreens.
