Kalm’s St. John’s-wort

Taxonomy

• Kingdom: Plantae
• Clade: Tracheophytes
• Clade: Angiosperms
• Clade: Eudicots
• Clade: Rosids
• Order: Malpighiales
• Family: Hypericaceae
• Genus: Hypericum
• Species: Hypericum kalmianum

Common Names by Region

• North America: Kalm’s St. John’s-wort, Kalm’s Hypericum
• Horticulture Trade: Shrubby St. John’s-wort

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Description

Growth Habit

• Perennial, deciduous shrub
• Densely branched with a compact, rounded form

Size

• Typically grows 2–3 feet (60–90 cm) in height
• Similar spread of 2–3 feet (60–90 cm)

Leaves

• Opposite, narrow lanceolate to oblanceolate
• Blue-green in color
• Semi-glossy, with a smooth margin
• Typically 1–2 inches (2.5–5 cm) in length

Flowers

• Bright yellow, 5-petaled, with prominent stamens
• Blooms June to August
• Flowers are ¾–1 inch (2–2.5 cm) in diameter
• Butterfly and pollinator-attracting

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Known Range

Native Range

• Great Lakes region of North America
• Found in Ontario, Michigan, Wisconsin, Minnesota, and surrounding states

Cultivated Range

• Widely cultivated as an ornamental in gardens and landscaping
• Hardy in USDA Zones 4–7

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Care Requirements

Light

• Prefers full sun (6+ hours of direct sunlight)
• Tolerates partial shade, but with reduced flowering

Watering

• Drought-tolerant once established
• Prefers moderate moisture, but adapts to dry conditions

Soil

• Well-drained, sandy or rocky soils preferred
• Tolerates poor, infertile, or alkaline soils
• Avoids heavy clay or wet soils

Humidity

• Adapted to moderate to dry climates
• Tolerates humidity but prefers good air circulation

Temperature

• Hardy in cold climates down to -30°F (-34°C)
• Does not tolerate extreme heat or excessive moisture

Propagation

• By seed (requires stratification)
• Softwood cuttings in late spring or early summer
• Division of mature plants possible but uncommon

Common Pests/Diseases

• Generally pest-free
• Occasionally affected by root rot in wet soils
• Rust, leaf spot, or blight may occur in high humidity

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Additional Notes

Special Features

• Attracts bees, butterflies, and other pollinators
• Erosion control—suitable for sandy, rocky, or disturbed soils
• Low-maintenance with seasonal interest

Maintenance Level

• Low—requires minimal care once established
• Prune lightly in late winter or early spring to maintain shape