A really lovely, small, summer-flowering shrub that I am sure many people would want in their gardens, if only they knew it. With fine-textured foliage, a hardy and adaptable disposition, and conical orange seed pods which continue the show through August, Kalm’s St. John’s Wort hardly needs more appeal, but I can add that it is a real draw for native bumblebees.
Kalm’s St. John’s Wort (Hypericum kalmianum) is named for Pehr Kalm, a disciple of Carl Linnaeus, who botanized along the shores of the Great lakes in the 1740’s. The shrub is almost a Great Lakes endemic – a plant found along the shores of the Great Lakes only — but unlike a strict Great Lakes endemic (Hill’s Thistle, Lake Iris and others), Kalm’s St. John’s Wort is native to in a few other places in the Great Lakes region, including the limestone shores of the Ottawa River. Our seed is as locally sourced as can be, collected from the Ottawa River shoreline in Bristol Township, Quebec.
In the rocky places where it grows in the wild, this shrub is often no more than a foot high. In gardens, it grows to about three feet, as tall as it is wide. It has a preference for calcareous (sweet) soils. Not that it is fussy, but it is not pleased by the acidic soils wanted by azaleas and blueberries. It likes lots of sun.