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Hypericum kalmianum is often confused with:
Hypericum prolificum Hypericum prolificum
Plants that fill a similar niche:
Baptisia alba Baptisia alba
Akebia quinata Five parted compound leaves.
Berberis thunbergii Berberis thunbergii berries

Saint Johnswort Hypericum kalmianum

Other Common Name(s):

Other plants called Saint Johnswort:

Phonetic Spelling
hy-PER-ih-kum kal-mee-AH-num
Description

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.

Diseases, Insect Pests, and Other Plant Problems:

No known diseases or insect pests.

See this plant in the following landscape:
Cultivars / Varieties:
'Deppe'
Tags:
#deciduous#drought tolerant#yellow flowers#blue-green leaves#herbaceous perennials#cold tolerant#fantz#compact habit#problem for cattle
 
Cultivars / Varieties:
'Deppe'
Tags:
#deciduous#drought tolerant#yellow flowers#blue-green leaves#herbaceous perennials#cold tolerant#fantz#compact habit#problem for cattle
  • 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.
  • 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
  • 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 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
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • Landscape:
    Landscape Location:
    Naturalized Area
    Rock Wall
    Slope/Bank
    Landscape Theme:
    Rock Garden
    Design Feature:
    Barrier
    Hedge
    Resistance To Challenges:
    Deer
    Drought
    Problems:
    Problem for Horses