perennial

Kalm's St. John's Wort

Hypericum perforatum 'Sunny Boulevard'

Not currently listed at our partner nurseries.

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Essentials

At a Glance

Plant Type

Perennial

Height

30 inches

Width

30 inches

Light

Full Sun, Partial Sun

Zones

4, 5, 6, 7

Water

Low to Moderate

Humidity

Average

Lifespan

Perennial Shrub

Native To

North America (Great Lakes region)

Toxicity

Toxic to livestock; can cause photosensitivity.

The Story

Plant Bio

Hypericum kalmianum, known as Kalm's St. John's Wort, is a compact, dense, mounded shrub native to the Great Lakes region. It features narrow, blue-green leaves and clusters of bright yellow, five-petaled flowers with prominent stamens in summer. 'Sunny Boulevard' is a particularly hardy and adaptable cultivar, selected for its tight, dense habit, prolific summer-long bloom of sunny yellow flowers, and attractive blue-green foliage. It is rust-resistant and requires little maintenance.

Bloom Period:

EarlyLate

Uses & Benefits:

Bright yellow flowers add cheerful color to gardens, attracting pollinators and birds.

Medicinal herb used for wound healing and mood enhancement.

Supports bees and butterflies, promoting pollination.

Marketplace

Where to Buy

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Planting

How to Grow

Tuck seeds into well-draining soil in early spring
Water regularly to keep soil moist but not waterlogged
Mist cuttings to encourage rooting in warm, bright spot
Divide mature plants every 3–4 years in early spring
Mulch around the base to retain moisture during summer
Transplant in early spring or fall for best results

Pro Tip

Ensure well-draining soil and full sun for optimal growth

Keep It Thriving

Care Guide

Do

Water during dry spells 🌱
Prune lightly after flowering
Apply balanced fertilizer in spring
Divide every 3–4 years

Don't

Overwater in winter ❌
Allow soil to become waterlogged ❌
Neglect pruning after bloom ❌
Use chemical pesticides unnecessarily ❌

Seasonal Care Calendar

Task	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Fertilize
Mulch
Propagate
Prune
Spring Cleanup

Watch Out For

Pests & Diseases

Common Pests

Common Diseases

In the Garden

Landscape Uses & Companions

Landscape Uses

Bright yellow border plantDrought-tolerant groundcoverMedicinal herb garden accent

Companion Plants

Lavender Echinacea Sedum Salvia Yarrow

Multiply

Propagation Methods

Good to Know

Common Questions

Kalm's St. John's Wort questions

What zones can Kalm's St. John's Wort grow in?

Kalm's St. John's Wort is hardy in USDA Zones 4–7. Inside that range it survives winter in the ground; outside it, grow it as an annual or a container plant you protect.

Is Kalm's St. John's Wort deer resistant?

Yes — Kalm's St. John's Wort is rated deer-resistant. Deer typically pass it over, though extreme hunger can override any plant's defenses.

When does Kalm's St. John's Wort bloom?

Kalm's St. John's Wort typically blooms in summer through late summer. Exact timing shifts a week or two with your zone — Sow's bloom calendar maps it to your garden.

Does Kalm's St. John's Wort need full sun?

Kalm's St. John's Wort does best in full sun to part shade. In hot climates, afternoon shade keeps blooms fresher longer.

Is Kalm's St. John's Wort drought tolerant?

Yes — once established (usually after the first full season), Kalm's St. John's Wort handles dry spells with minimal watering. Water deeply its first year to build the root system that makes that possible.