Free Shipping on Orders Over $75! Automatically Save 15% on Orders Over $119!

Almanac Planting Co Ageratum houstonianum 'Blue Horizon' Flower Image

Ageratum 'Blue Horizon'

Regular price
Sale price
Regular price
Sold out
Unit price
Shipping calculated at checkout.

Ageratum houstonianum 'Blue Horizon'


Uses: Annual flowering plant 

Benefits: Easy to take care of. Produces lavender to purplish-blue flowers that typically start in June and last until frost. 

Zones: 2 - 11 

Sun: Full

Life Cycle: Annual

Mature Height: 30"

Mature Width: 18"


Ageratum houstonianum 'Blue Horizon'—commonly known as Blue Horizon Floss Flower—is a medium size, frost-tender annual that's best known for its clusters of lovely, fluffy flowers which resemble asters. Flower production is typically constant from late-spring until mid-fall. 

'Blue Horizon' is a taller than average cultivar of Ageratum houstonianum, making it especially well suited for producing flowers that are great for use in freshly cut floral arrangements. 

Growing in a shapely mound, it produces larger flowers than traditional ageratums, which it supports via its strong, sturdy stems. 

Ageratums are known to attract various pollinators such as bees and butterflies. 

Perfect for a variety of areas, especially rock gardens, mid-borders, patios, and mixed containers. 


Ageratum Care

Ageratum houstonianum 'Blue Horizon' does best in full sun, although partial shade is also acceptable. The plant may benefit if very strong afternoon sun is blocked by a source of partial shade, especially in hot, dry areas. 

Plant after the last spring frost, ideally when temperatures are above 50°F.

Floss Flower requires soil that is moist, but not wet. Irrigate during establishment, and during periods of drought. Do not allow this plant's soil to completely dry! Avoid overhead watering to mitigate the risk of powdery mildew. 

Fertilize as required, especially if planted in poor soil. 

Does best in temperatures between 65°F and 95°F.

Although unnecessary, the deadheading of spent flowers will encourage blooming, and help to ensure a tidy plant. 


Size of Amaranth for Sale

The Ageratum houstonianum 'Blue Horizon' that we sell online will ship in a 4" grow pot. Each plant will be appropriately sized for its pot. 

Size of Amaranth When Fully Grown

Ageratum houstonianum 'Blue Horizon' typically grows to a height of 30" and a width of 18". It sometimes grows as small as 6" wide and 12" tall. 

Additional Information

Common Names of Ageratum houstonianum 'Blue Horizon'

  • Ageratum 'Blue Horizon'

  • Floss Flower 'Blue Horizon'

Toxicity and Risks of Amaranth

All parts of Ageratum houstonianum 'Blue Horizon' are considered toxic if ingested. This is due to the fact that they contain pyrrolizidine alkaloids, which is known to cause liver lesions.