annual RHS Award

Blue Horizon Floss Flower

Ageratum houstonianum 'Blue Horizon'

Not currently listed at our partner nurseries.

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Essentials

At a Glance

Plant Type

Annual

Height

28 inches

Width

12 inches

Light

Full Sun, Partial Sun

Water

Moderate

Humidity

Moderate

Lifespan

Annual

Native To

Central America

Toxicity

Mildly toxic if ingested

The Story

Plant Bio

Ageratum houstonianum 'Blue Horizon' is a compact, bushy annual known for its fluffy blue flowers. This cultivar is particularly noted for its vibrant blue color and strong resistance to pests.

Uses & Benefits:

Ageratum Blue Horizon provides vibrant blue flowers that brighten garden borders and containers, attracting pollinators and adding long-lasting color.

Easy to grow and maintain, it is ideal for beginners and low-maintenance gardening.

Supports bees and butterflies, enhancing local pollinator activity.

Marketplace

Where to Buy

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

Shipping costs Year-round shipping Free shipping

Planting

How to Grow

Tuck seeds into well-draining soil in early spring for best germination.
Mist cuttings regularly to maintain humidity and promote rooting.
Transplant seedlings outdoors after the last frost date, typically 6 weeks later.
Water consistently to keep soil moist but not soggy during the growing season.
Pinch back early growth to encourage bushier plants and more blooms.
Fertilize monthly with a balanced liquid fertilizer for continuous flowering.

Pro Tip

Use seed-starting mix and provide full sun for vibrant, prolific blooms.

Keep It Thriving

Care Guide

Do

Water regularly to keep soil evenly moist 💧
Pinch back to promote bushier growth
Apply fertilizer monthly during the growing season
Deadhead spent blooms to encourage more flowers

Don't

Avoid overwatering which can lead to root rot ❌
Don't plant in heavy, poorly-draining soil
Skip fertilizing during dormant periods
Avoid neglecting pests and diseases

Seasonal Care Calendar

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

Watch Out For

Pests & Diseases

Common Pests

Common Diseases

In the Garden

Landscape Uses & Companions

Landscape Uses

Bright, cheerful border with vibrant blue flowersContainer plant for patios and decksWildflower garden accent with a pop of color

Companion Plants

Marigolds Petunias Salvia Lobelia Sweet Potato Vine

Multiply

Propagation Methods

Good to Know

Common Questions

Blue Horizon Floss Flower questions

What zones can Blue Horizon Floss Flower grow in?

Blue Horizon Floss Flower is hardy in USDA Zone 10. Inside that range it survives winter in the ground; outside it, grow it as an annual or a container plant you protect.

Is Blue Horizon Floss Flower deer resistant?

Yes — Blue Horizon Floss Flower is rated deer-resistant. Deer typically pass it over, though extreme hunger can override any plant's defenses.

When does Blue Horizon Floss Flower bloom?

Blue Horizon Floss Flower typically blooms in summer to frost through early fall. Exact timing shifts a week or two with your zone — Sow's bloom calendar maps it to your garden.

Does Blue Horizon Floss Flower need full sun?

Blue Horizon Floss Flower does best in full sun to part shade. In hot climates, afternoon shade keeps blooms fresher longer.