Hypericum kalmianum aka Kalm's St. John's Wort

Hypericum kalmianum is known as Kalm's St. John's wort. This small shrub belongs to the Hypericaceae family. It grows wild around the Great Lakes in North America. Its range includes Ontario, Quebec, and several northern US states. Wild plants grow beside lakes, rivers, and cliffs. They also occur in sandy woods and rocky ground. Illinois lists the species as endangered within the state.

In gardens, it forms a mound with upright branches. Most plants reach 2–3 feet [0.61–0.91 metres] tall and wide. Some reach 4 feet [1.22 metres] in height. Growth is slow, and the woody roots spread near the surface. Leaves may stay through winter, though some plants lose them. The narrow, blue-green leaves grow in pairs without clear stalks. Their smooth edges curl down, and small glands dot them. Young green stems have four angles and no hairs. Older branches become rounder, with brown to reddish bark. This bark peels into thin strips, adding winter interest.

Golden flowers open in July and August, attracting bees and butterflies. Bees gather pollen from the many stamens at each flower's centre. Flowers usually have five petals and form small clusters. Each measures about 1–1.5 inches across. Bloom can last about a month. Small seed capsules follow the flowers and turn dark red. They later appear brown and may remain until spring. Each capsule has five chambers holding many small, dark seeds.

Grow this shrub in full sun or partial shade. It prefers moist soil that drains well. Rich sandy loam suits it, but poor soil also works. It accepts clay, loam, sand, and a broad pH range. Established plants withstand some drought and dry soil. They also tolerate brief spells of shallow standing water. Chicago Botanic Garden gives a USDA hardiness range of 4–7. Prune after flowering if needed to keep its shape. Do not cut the whole shrub down to ground level.

Use it for low hedges, borders, or foundation beds. It also suits rock gardens, slopes, and pond edges. Its flowers support pollinator gardens, while peeling bark adds winter interest. Sources report no serious pest or disease problems. Deer may browse the shrub. Its leaves are toxic to livestock and can cause gut irritation. They can also increase sun sensitivity, leading to skin irritation.