Plant Profile

Kalm's St. John's Wort - (Hypericum kalmianum) is a compact perennial evergreen shrub, at maturity it can reach a height of 4 feet. The genus name, Hypericum, comes from the Greek words hyper meaning above, and eikon meaning picture. This references the practice of hanging flowers from this genus above images, pictures, or windows. The species name, kalmianum, honors Peter Kalm, a student of Linnaeus, who reportedly discovered this plant in the wild in North America in the mid-1700s.

This plant is native to Eastern Canada and the Northeastern and North Central United States. This plant is often found along lakes, rivers, and cliffs in the wild.  It is drought tolerant and is considered the most cold-hardy of the hypericum. Kalm's St. John's Wort is a flowering shrub with numerous 1-inch yellow flowers over a month-long blooming period in mid to late summer. It also boasts a woody root system that is shallow and spreading.

The plant prefers full sun, wet to moist conditions, and well-drained soil containing calcareous sand or limestone. Shallow water is tolerated if it is temporary. It also tolerates a range of soil types, including drought, and dry soil. 

Various bees collect pollen from the flowers, and the shrub is browsed by Whitetail Deer. Kalm's St. John's Wort has a somewhat formal appearance and may be used in the landscape as a low hedge, border planting, or foundation planting. Other considerations would be: planted for added interest in a Rock Garden or plant in mass.