Hypericum kalmianum
Common Name(s):
- Phonetic Spelling
- hy-PER-ih-kum kal-mee-AH-num
- Description
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Kalm's St. John's Wort is a perennial, herbaceous, deciduous or evergreen shrub or small tree that, at maturity, can reach a height of 3 feet. It is drought tolerant and more loose and open in form than other of the more than 400 species of hypericum. It is also 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 has a woody root system that is shallow and spreading. Prune if needed after bloom in late summer. 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 species name honors Peter Kalm, a student of Linnaeus, who reportedly discovered this plant in the wild in North America in the mid-1700s.
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, drought, and dry soil. The leaves of this St. John's Wort species are toxic to domesticated farm animals, particularly those with white or thin fur because these plants contain a toxin that increases sensitivity to sunlight, causing irritation of the skin. Consumption of these plant species can also irritate the gastrointestinal tract of these animals.
Insects, Diseases, and Other Plant Problems: No known diseases or insect pests.
VIDEO created by Grant L. Thompson for “Trees, Shrubs, and Woody Vines for Landscaping” a plant identification course offered by the Department of Horticulture at Iowa State University.
- Profile Video:
- See this plant in the following landscape:
- Cultivars / Varieties:
- 'Deppe'
- Tags:




- Cultivars / Varieties:
- 'Deppe'
- Tags:
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Attributes:
- Genus:
- Hypericum
- Species:
- kalmianum
- Family:
- Hypericaceae
- Life Cycle:
- Perennial
- Woody
- Recommended Propagation Strategy:
- Division
- Root Cutting
- Country Or Region Of Origin:
- Northeastern United States and Canada
- Distribution:
- DC , IL , IN , MI , NY , OH , WI
- Edibility:
- Toxic to livestock.
- Dimensions:
- Height: 2 ft. 0 in. - 3 ft. 0 in.
- Width: 2 ft. 0 in. - 3 ft. 0 in.
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Whole Plant Traits:
- Plant Type:
- Perennial
- Shrub
- Woody Plant Leaf Characteristics:
- Broadleaf Evergreen
- Deciduous
- Habit/Form:
- Dense
- Erect
- Mounding
- Multi-stemmed
- Rounded
- Growth Rate:
- Slow
- Maintenance:
- Low
- Texture:
- Medium
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Cultural Conditions:
- Light:
- Full sun (6 or more hours of direct sunlight a day)
- Partial Shade (Direct sunlight only part of the day, 2-6 hours)
- Soil Texture:
- Clay
- Loam (Silt)
- Sand
- Soil pH:
- Acid (<6.0)
- Alkaline (>8.0)
- Neutral (6.0-8.0)
- Soil Drainage:
- Good Drainage
- Moist
- Occasionally Dry
- Occasionally Wet
- Available Space To Plant:
- 3 feet-6 feet
- USDA Plant Hardiness Zone:
- 4b, 4a, 5b, 5a, 6b, 6a, 7b, 7a
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Fruit:
- Fruit Color:
- Brown/Copper
- Fruit Value To Gardener:
- Showy
- Display/Harvest Time:
- Fall
- Fruit Type:
- Capsule
- Fruit Length:
- < 1 inch
- Fruit Description:
- Flowers are replaced by seed capsules about 1/3 of an inch long that are lanceoloid in shape and 5-lobed. The interior of each seed capsule has 5 completely separated cells; there are numerous seeds in each cell. These seeds are dark-colored, narrowly oblongoid, and somewhat flattened.
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Flowers:
- Flower Color:
- Gold/Yellow
- Flower Inflorescence:
- Corymb
- Flower Value To Gardener:
- Showy
- Flower Bloom Time:
- Summer
- Flower Petals:
- 4-5 petals/rays
- Flower Size:
- 1-3 inches
- Flower Description:
- Upper stems terminate in corymbs or compound corymbs of 3 to 7 flowers. Solitary or cymose, terminal or axillary. Yellow (usually) 5-petaled (rarely 4), 5 sepals (rarely 4); stamens numerous, in bundles or in showy boss.
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Leaves:
- Woody Plant Leaf Characteristics:
- Broadleaf Evergreen
- Deciduous
- Leaf Color:
- Blue
- Green
- Leaf Type:
- Simple
- Leaf Arrangement:
- Opposite
- Whorled
- Leaf Shape:
- Linear
- Oblanceolate
- Oblong
- Leaf Margin:
- Entire
- Hairs Present:
- No
- Leaf Length:
- 1-3 inches
- Leaf Width:
- < 1 inch
- Leaf Description:
- Pairs of opposite primary leaves occur along the young stems. There are often clusters of smaller secondary leaves near the axils of the opposite primary leaves. These leaves are up to 2 inches long and 1/3 of an inch across; they are linear-oblong to oblanceolate in shape and their margins are entire (toothless) and revolute (rolled downward). The upper leaf surface is bluish green to medium green, glabrous, and sometimes glaucous, while the lower leaf surface is light green, glabrous, and sometimes glaucous. All leaves are sessile or nearly so.
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Bark:
- Bark Color:
- Light Brown
- Red/Burgundy
- Surface/Attachment:
- Exfoliating
- Bark Description:
- Branches near the base of this shrub have yellowish brown to reddish brown papery bark that often becomes shredded into white strips or narrow sheets.
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Stem:
- Stem Color:
- Green
- Stem Is Aromatic:
- No
- Stem Surface:
- Smooth (glabrous)
- Stem Description:
- Young stems are light green, glabrous, and 4-angled. Contains 2 to 4 (up to 6) ridges on newer growth, smooth and rounded on older growth.
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Landscape:
- Landscape Location:
- Naturalized Area
- Rock Wall
- Slope/Bank
- Landscape Theme:
- Rock Garden
- Design Feature:
- Barrier
- Border
- Hedge
- Mass Planting
- Resistance To Challenges:
- Deer
- Drought
- Problems:
- Problem for Horses