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This gorgeous, yellow-flowered shrub is a stunner when in full bloom. The rounded, multi-branched beauty grows up to 3 feet tall with bluish-green foliage and five-petaled flowers bearing generous clumps of fluffy, yellow filaments. The bark often shreds or peels, providing winter interest. The plant prefers moist or wet soils and full sun, but it adapts to average, well-drained soils and part shade. It tolerates shallow standing water if temporary, and it's resistant to deer and proximity to black walnut trees. Due to overshading by woody species, it has a threatened status in Ohio, where it's found mainly in the northern counties and on the dunes and rocky shores of Lake Erie. It's shorter in stature than H. prolificum, which is more common in Ohio, and it lacks the medicinal properties of H. perforatum, an invasive non-native.  

 

The 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. The specific epithet refers to Peter Kalm, a student of Linnaeus, who reportedly discovered this plant in the wild in North America in the mid-1700s. 

 

Native habitats include moist, sunny openings on sandy or gravelly soils; shores; swales; dunes; and low prairies. Plant en masse to create a low hedge. Beautiful addition to borders, rock gardens, wood margins, rocky slopes, wild gardens, naturalized areas, or pond peripheries.

 

Plant Characteristics:

Grows 2-3' tall and wide.

 

Prefers full or part sun; flowers best in full sun.

 

Prefers moist to wet sandy soils but adapts to average conditions.

Flowers bloom July-August and have 5 spreading petals about 1" wide, 5 light-green sepals, light-yellow pistil with 5 styles, and numerous stamens. The flowers lack nectar. Seed capsules have 5 lobes, each containing many seeds.

 

Pairs of opposite primary leaves grow on young stems. Often, clusters of smaller secondary leaves up to 2" long occur near the axils of the primary leaves. Leaves are linear-oblong to oblanceolate in shape with smooth margins that roll downward (revolute). Upper leaf surface is bluish green to medium green.

 

Woody branches near the base have yellowish-brown to reddish-brown bark that shreds into white strips or narrow sheets. Stems are four angled.

 

Wildlife Value:

Host plant for 23 species of Lepidoptera larvae, including burgundy St. johnswort moth, gray half-spot, and 3 other specialist moths. Various bees are the primary pollinators.  

 

Medicinal, Edible, and Other Uses:

 

Resources:

The Buckeye Botanist: https://floraofohio.blogspot.com/2012/09/

 

Ohio Dept. of Natural Resources: https://ohiodnr.gov/discover-and-learn/plants-trees/flowering-plants/dwarf-iris

 

Illinois Wildflowers: https://www.illinoiswildflowers.info/wetland/plants/kalm_stjohn.html

 

Missouri Botanical Garden: https://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?taxonid=279217

 

Scioto Gardens: https://sciotogardens.com/product/hypericum-kalmianum-2-kalms-st-johns-wort/

 

 

St. John’s Wort, Kalm's, Hypericum kalmianum

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