search

TREES & plants

Kalm's St. John's Wort

Kalm's St. John's wort in flower.

A sun-loving, low-growing, 2 to 3 feet high, native shrub found in moist, low areas in the Upper Great Lakes. The long-blooming, bright yellow summer flowers have showy, pompom-like stamens. Best used in mass for full effect.

"This species is native to the Chicago Region according to Swink and Wilhelm's Plants of the Chicago Region, with updates made according to current research."   

 

This plant has some cultivated varieties. Go to list of cultivars.

 

Botanical name: 
Hypericum kalmianum
All Common Names: 
Kalm's St. John Wort, Kalm's hypericum, Kalms St. John Wort, Kalm's Saint Johnwort
Family (English): 
Hypericum
Family (Botanic): 
Hypericaceae
Tree or Plant Type: 
  • Shrub
Native Locale: 
  • Chicago area, 
  • North America
Landscape Uses: 
  • Container, 
  • Foundation, 
  • Massing, 
  • Patio/sidewalk
Size Range: 
  • Small shrub (3-5 feet), 
  • Low-growing shrub (under 3 feet)
Light Exposure: 
  • Full sun (6 hrs direct light daily)
Hardiness Zones: 
  • Zone 4, 
  • Zone 5 (Chicago), 
  • Zone 6, 
  • Zone 7
Soil Preference: 
  • Moist, well-drained soil
Season of Interest: 
  • Early summer, 
  • Mid summer, 
  • Late summer, 
  • Early fall
Flower Color & Fragrance: 
  • Yellow
Shape or Form: 
  • Round, 
  • Thicket-forming
Growth Rate: 
  • Moderate
More Information: 

Tree & Plant Care

Best in full sun in moist to well drained soils.
Flowers on new wood, prune in spring.

Disease, pests, and problems

Leaf spots.

Disease, pest, and problem resistance

Tolerant of salt, drought and soil compaction.

Native geographic location and habitat

C-Value: 10
Found in moist soils near ponds and dune areas around the Upper Great Lakes region.

Attracts birds, pollinators, or wildlife

Birds and butterflies are attracted to flowers and seeds.

Bark color and texture 

Twigs are slender, reddish-brown, older stems have exfoliating bark exposing a bronzy colored inner bark.

Leaf or needle arrangement, size, shape, and texture

Alternate, 1/2 inch wide linear to oblong leaves up to 5 inches long.
Medium bluish-green upper leaf with small glandular dots beneath.

Flower arrangement, shape, and size

Bright yellow, 5-petaled flowers with pompom-like stamens. Long blooming.

Fruit, cone, nut, and seed descriptions

Brown capsules about 1/4-inch long, persist into winter.

Cultivars and and their differences 

Ames St John Wort (Hypericum kalmianum 'Ames'): A small, 2 to 2 1/2 feet high and wide, rounded shrub from Iowa State introduction program, 1-inch wide golden yellow flowers in summer, extremely hardy.

Gemo St. Johns Wort (Hypericum kalmianum 'Gemo'): 2 to 3 feet high, narrow, willow-like leaves, small yellow flowers with bushy stamens.

Sunny Boulevard™ St John's Wort (Hypericum kalmianum 'Deppe'): A 2 to 3 feet high and wide shrub with small, bright yellow flowers.

 

Hypericum kalmianum or Kalm's St. John's Wort