Plant DetailShow Menu

Hypericum kalmianum is often confused with:
Hypericum prolificum Hypericum prolificum
Plants that fill a similar niche:
Salvia rosmarinus Rosmarinus officinalis
Ilex crenata Ilex crenata
Erica carnea Erica carnea 'Challenger'

Kalm's St. John's Wort Hypericum kalmianum

Previously known as:

  • Hypericum lanatum
  • Norysca kalmiana
Phonetic Spelling
hy-PER-ih-kum kal-mee-AH-num
Description

Kalm's St. John's Wort is a compact perennial, herbaceous, deciduous, or evergreen shrub or subshrub that, at maturity, can reach a height of 4 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.

This plant is native to Eastern Canada and the Northeastern and North Central United States. It is found along lakes, rivers, and cliffs in the wild. It may be found along Lake Michigan and Lake Huron.  The shrub is native to Illinois and is listed as endangered. In protected areas of Illinois, this shrub appears to be increasing. 

The genus name, Hypericum, comes from the Greek words hyper meaning above, and eikon meaning picture. This references the practice of hanging flowers from this genus above images, pictures, or windows. The species name, kalmianum, 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, including drought, and dry soil. Pruning, if needed to maintain the plant's shape, should be done after flowering has ended or in late fall; however, you should never cut the shrub back to the ground.

Various bees collect pollen from the flowers, and the shrub is browsed by White-tail Deer. 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, irritating the skin. Consumption of these plant species can also irritate the gastrointestinal tract of these animals. 

Kalm's St. John's Wort has a somewhat formal appearance and may be used in the landscape as a low hedge, border planting, or foundation planting. Planted for added interest in a Rock Garden or plant in mass.

Seasons of Interest:

Bloom:  Summer     Foliage:  Spring, Summer, and Fall     Fruits:  Fall, persist until Spring

Quick ID Hints:

  • dense mounding, rounded, or ball-like broadleaf evergreen to a semi-evergreen shrub or subshrub up to 4 feet tall 
  • leaves are opposite, narrow, linear, bluish-green, and dotted with small glands 
  • 4-angled stems
  • five-petaled golden yellow flowers that are 1.5 inches in diameter and borne on 3 to 7 flowered cymes during the summer and bloom for 1 month
  • fruits or beaked, oval, brown seed capsules
  • yellowish-brown, orangish-brown to reddish-brown bark

Insects, Diseases, and Other Plant Problems: This plant has 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:
#deciduous#full sun tolerant#drought tolerant#shrub#slow growing#yellow flowers#broadleaf evergreen#low maintenance#winter interest#slopes#mass planting#hedges#mounding#blue-green leaves#low growing plant#herbaceous perennials#frost tolerant#long bloom time#rounded#rock garden#cutting garden#pollinator plant#subshrub#fantz#compact habit#problem for cattle#pollinator garden#landscape plant sleuths course#border
 
Cultivars / Varieties:
'Deppe'
Tags:
#deciduous#full sun tolerant#drought tolerant#shrub#slow growing#yellow flowers#broadleaf evergreen#low maintenance#winter interest#slopes#mass planting#hedges#mounding#blue-green leaves#low growing plant#herbaceous perennials#frost tolerant#long bloom time#rounded#rock garden#cutting garden#pollinator plant#subshrub#fantz#compact habit#problem for cattle#pollinator garden#landscape plant sleuths course#border
  • Attributes:
    Genus:
    Hypericum
    Species:
    kalmianum
    Family:
    Hypericaceae
    Life Cycle:
    Perennial
    Woody
    Recommended Propagation Strategy:
    Division
    Root Cutting
    Country Or Region Of Origin:
    Eastern Canada and North Central to Northeastern United States
    Distribution:
    Native: United States--IL, IN, MI, MN, NY, OH, and WI; Canada--Ontario and Quebec. Introduced: DC
    Wildlife Value:
    Attracted by pollinators including bees and butterflies. Browse by White-tail Deer.
    Play Value:
    Attractive Flowers
    Attracts Pollinators
    Colorful
    Easy to Grow
    Edibility:
    Toxic to livestock.
    Dimensions:
    Height: 2 ft. 0 in. - 4 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 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
    NC Region:
    Mountains
    Piedmont
    USDA Plant Hardiness Zone:
    4a, 4b, 5a, 5b, 6a, 6b, 7a, 7b
  • Fruit:
    Fruit Color:
    Brown/Copper
    Red/Burgundy
    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. The capsule turns dark red as it matures.
  • Flowers:
    Flower Color:
    Gold/Yellow
    Flower Inflorescence:
    Corymb
    Flower Value To Gardener:
    Good Cut
    Long Bloom Season
    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. Each flower measures 1 to 1.25 inches in diameter. The petals are medium yellow to golden yellow and are oblong to obovate. The five green sepals are lanceolate and are half as long as the petals. Blooming occurs from mid-summer to late summer and generally lasts about 1 month.
  • 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
    Orange
    Red/Burgundy
    Surface/Attachment:
    Exfoliating
    Bark Description:
    Branches near the base of this shrub have yellowish-brown, orangish-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:
    Pollinator Garden
    Rock Garden
    Design Feature:
    Barrier
    Border
    Foundation Planting
    Hedge
    Mass Planting
    Attracts:
    Bees
    Butterflies
    Resistance To Challenges:
    Deer
    Drought
    Salt
    Problems:
    Problem for Horses