FlowerAgeratum
Blue Horizon Ageratum
Bedding Flower
Blue Horizon Ageratum is a striking annual flower that brings globe-shaped blooms of exotic blue to gardens across hardiness zones 3-11. Native to the tropical regions of Central America and Mexico, this cultivar grows 24-30 inches tall and produces continuous summer-to-fall color from seed to bloom in 84-91 days. The flowers are irresistibly attractive to pollinators and deer leave them alone, making this an excellent choice for gardens where you want reliable, uninterrupted color without constant replanting or pest pressure.
Photo © True Leaf Market(https://www.trueleafmarket.com/products/ageratum-blue-horizon-flower-seeds)
Growing Conditions
USDA Zone
3-11
Sunlight
Full Sun
Water
Moderate
Soil
Well-drained, Fertile Loam
Preferred Temp60-75°F
Growth Stats
30 in
Height
18 in
Width
PeriodAnnual
TypeBush
Spacing
12-15 inches apart
Plant Profile
Sunlight
Full Sun
Water
Moderate
Zones
3-11
Size
30in H x 18in W
Growth
Annual
Care
High
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Highlights
Blue Horizon produces some of the season's most distinctive globe-shaped flower heads with an exotic presence that feels far more sophisticated than typical garden ageratums. It germinates reliably at 70-75°F and blooms continuously from mid-summer through the first frost, thriving in full sun with moderate water. The upright growth habit reaches 24-30 inches, giving it real presence in beds and borders rather than disappearing into the landscape.
Common Uses
Blue Horizon Ageratum is grown as an ornamental flower for garden beds, borders, and rock gardens. The globe-shaped blue blooms provide continuous color from mid-summer through fall, working well in mixed plantings where consistent, long-season color is desired. The upright growth habit and pollinator-attracting flowers make it valuable in gardens designed to support beneficial insects.
Growing Timeline
First Bloom
Early Summer
First Harvest
Not Applicable
Last Harvest
Not Applicable
Care Instructions
Start Indoors
Sow indoors 6-8 weeks before your last frost date. Surface sow seeds and press them lightly into soil, as they require light to germinate. Keep soil at 75°F until germination (5-14 days), then lower temperature to 60-65°F. Water from below by placing trays in a larger water tray and allowing drainage; this prevents damping off and avoids disturbing tiny seeds.
Transplant Outdoors
Harden off seedlings gradually over a week, then transplant outdoors about 1-2 weeks after your last frost date when soil has warmed and frost risk has passed. Space plants 1 inch apart in rows 24 inches apart, or adjust spacing based on your desired mature width of 12-18 inches.
Direct Sow
Direct sow about 1-2 weeks after your last frost date for flowers mid-summer to fall. Surface sow and press seeds lightly; they need light to germinate.
Pruning
Deadhead spent blooms regularly to encourage continuous flowering throughout the season. The upright growth habit benefits from this maintenance, keeping plants compact and productive rather than becoming leggy or sparse.
Growing Calendar
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Companion Planting
Pests & Diseases
Ecology & Traits
Deer ResistantAttracts Pollinators
Soil pH Range
6 – 7
Bloom Time
Summer To Fall
Scientific Classification
Ageratum houstonianum Mill.
Family
Asteraceae
Genus
Ageratum
Duration
Annual, Perennial
Growth Habit
Forb/herb
Native Status
L48 (I)HI (I)
History & Origin
“Ageratum houstonianum originates from the humid tropical gardens of Central America and Mexico, where it evolved as a heat-loving annual. The Blue Horizon cultivar represents the plant's journey from its native range into American seed catalogs, where it has been refined and selected for the reliable globe-shaped flower heads and reliable blue color that distinguish it today. This variety carries the tropical genetics of its ancestors while being adapted for cultivation across North American gardens.”