annual

Black Gem Cornflower

Centaurea cyanus 'Black Gem'

Not currently listed at our partner nurseries.

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Essentials

At a Glance

Plant Type

Annual

Height

30 inches

Width

12 inches

Light

Full Sun, Partial Sun

Zones

4, 5, 6, 7, 8, 9

Water

Moderate

Humidity

Average

Lifespan

Annual

Native To

Europe

Toxicity

Non-toxic to humans and pets

The Story

Plant Bio

Hardy annual with lance-shaped, grey-green leaves. Produces double, thistle-like flowerheads of a deep chocolate-maroon color, appearing almost black. The 'Black Gem' cultivar is prized for its dramatic, dark flowers which provide a striking contrast in cottage gardens, wildflower meadows, and cutting gardens.

Bloom Period:

EarlyLate

Uses & Benefits:

Centaurea cyanus 'Black Gem' offers striking dark-hued flowers that add dramatic contrast to garden beds. Its vibrant blooms attract pollinators and bring visual interest from late spring through summer.

This hardy annual helps control soil erosion, suppress weeds, and requires minimal maintenance, making it ideal for sustainable gardening.

Provides nectar for bees and butterflies, supporting local biodiversity and healthy pollinator populations.

Marketplace

Where to Buy

We couldn't find this plant listed online right now.

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Planting

How to Grow

Tuck seeds into well-draining soil in early spring for best germination.
Mist cuttings regularly to maintain humidity and encourage rooting.
Plant in full sun to promote vibrant blooms and healthy growth.
Water consistently, keeping soil moist but not waterlogged during the growing season.
Fertilize monthly with a balanced, water-soluble fertilizer for optimal flowering.
Divide mature plants in early spring or fall to rejuvenate and propagate.

Pro Tip

Sow seeds directly outdoors for natural growth, or start indoors 6 weeks before last frost for earlier blooms.

Keep It Thriving

Care Guide

Do

Provide full sun for at least 6 hours daily 🌞
Water regularly during dry spells to keep soil moist
Deadhead spent flowers to encourage more blooms
Fertilize monthly with a balanced fertilizer
Divide plants every 2-3 years to maintain vigor

Don't

Avoid overwatering to prevent root rot ❌
Do not plant in heavy, poorly-draining soil
Refrain from excessive fertilizing which can lead to weak stems
Avoid planting in shaded areas where flowers may be sparse
Do not neglect deadheading to prolong flowering

Seasonal Care Calendar

Task	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Deadhead
Harvest
Plant

Watch Out For

Pests & Diseases

Common Pests

Common Diseases

In the Garden

Landscape Uses & Companions

Landscape Uses

Vivid blue flowered borderWildflower meadow accentButterfly attracting garden feature

Companion Plants

Coreopsis Black-eyed Susan Lavender Echinacea Yarrow

Multiply

Propagation Methods

Good to Know

Common Questions

Black Gem Cornflower questions

What zones can Black Gem Cornflower grow in?

Black Gem Cornflower is hardy in USDA Zones 4–10. Inside that range it survives winter in the ground; outside it, grow it as an annual or a container plant you protect.

Is Black Gem Cornflower deer resistant?

Yes — Black Gem Cornflower is rated deer-resistant. Deer typically pass it over, though extreme hunger can override any plant's defenses.

When does Black Gem Cornflower bloom?

Black Gem Cornflower typically blooms in late spring through early summer. Exact timing shifts a week or two with your zone — Sow's bloom calendar maps it to your garden.

Does Black Gem Cornflower need full sun?

Black Gem Cornflower does best in full sun to part shade. In hot climates, afternoon shade keeps blooms fresher longer.

Is Black Gem Cornflower drought tolerant?

Yes — once established (usually after the first full season), Black Gem Cornflower handles dry spells with minimal watering. Water deeply its first year to build the root system that makes that possible.