Kalm's St. John's Wort (Hypericum kalmianum)

Common names:
Give a thumbs up Kalm's St. John's Wort
Give a thumbs up Kalm's St. Johnswort

General Plant Information (Edit)
Plant Habit: Shrub
Life cycle: Perennial
Sun Requirements: Full Sun
Full Sun to Partial Shade
Water Preferences: Mesic
Soil pH Preferences: Strongly acid (5.1 – 5.5)
Moderately acid (5.6 – 6.0)
Slightly acid (6.1 – 6.5)
Neutral (6.6 – 7.3)
Slightly alkaline (7.4 – 7.8)
Moderately alkaline (7.9 – 8.4)
Minimum cold hardiness: Zone 4a -34.4 °C (-30 °F) to -31.7 °C (-25 °F)
Maximum recommended zone: Zone 7b
Plant Height: 2-3 feet
Plant Spread: 2-3 feet
Leaves: Evergreen
Fruit: Showy
Other: small dry brown 5-parted (4 to 6 possible) capsules
Fruiting Time: Fall
Late fall or early winter
Flowers: Showy
Flower Color: Yellow
Bloom Size: 1"-2"
Flower Time: Summer
Late summer or early fall
Uses: Windbreak or Hedge
Wildlife Attractant: Bees
Resistances: Flood Resistant
Drought tolerant
Salt tolerant
Pollinators: Various insects
Miscellaneous: Monoecious

shrubs in yellow bloom

Photo gallery:
Location: Morton Arboretum in Lisle, IllinoisDate: 2016-07-18shrubs in yellow bloom
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Location: Morton Arboretum in Lisle, IllinoisDate: 2016-07-18foliage and flowers
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Posted by ILPARW (southeast Pennsylvania - Zone 6b) on Aug 16, 2018 8:24 PM

The Kalm St. Johnswort is native to central Wisconsin to all around Lakes Michigan, Huron, and Erie in bogs, dunes, and on cliffs in dry to draining wet soils in muds to rocky--sandy soils that are moderately acid to quite alkaline. The bluish-green leaves are whitish bloomy beneath and about 1 to 2 inches long. Flowers about 1/2 to 1 inch in diameter; slightly fragrant. The dry brown capsules are 4 to 6 celled. The root system is shallow and fibrous and it is easy to transplant. It is sold by native plant nurseries and some larger, diverse conventional nurseries. It is not a common plant in landscapes, just very occasionally used here and there, mostly by landscape architects and garden enthusiasts.

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Discussion Threads about this plant
Thread Title Last Reply Replies
Will the offspring of a flowering shrub produce flowers? by mtresp Jul 19, 2016 10:41 AM 2
I know what it is. by LindaTX8 May 23, 2012 8:12 PM 3

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