Ageratum, Floss Flower, Flossflower 'Blue Horizon'

Ageratum houstonianum

Family: Asteraceae (ass-ter-AY-see-ee) (Info)
Genus: Ageratum (ad-jur-RAY-tum) (Info)
Species: houstonianum (hoos-toh-nee-AH-num) (Info)
Cultivar: Blue Horizon
Synonym:Ageratum mexicanum



Water Requirements:

Average Water Needs; Water regularly; do not overwater

Sun Exposure:

Full Sun



Foliage Color:

Medium Green


12-18 in. (30-45 cm)


6-9 in. (15-22 cm)


Not Applicable

Where to Grow:

Unknown - Tell us


Unknown - Tell us

Bloom Color:

Medium Purple

Bloom Characteristics:

This plant is attractive to bees, butterflies and/or birds

Flowers are fragrant

Bloom Size:

Unknown - Tell us

Bloom Time:

Mid Summer

Late Summer/Early Fall

Other details:

Unknown - Tell us

Soil pH requirements:

6.1 to 6.5 (mildly acidic)

6.6 to 7.5 (neutral)

7.6 to 7.8 (mildly alkaline)

Patent Information:

Unknown - Tell us

Propagation Methods:

From seed; sow indoors before last frost

From seed; direct sow after last frost

Seed Collecting:

N/A: plant does not set seed, flowers are sterile, or plants will not come true from seed


This plant is said to grow outdoors in the following regions:

Richmond, California

San Jose, California

Santa Maria, California

Deltona, Florida

Dunnellon, Florida

Fort Lauderdale, Florida

Kailua, Hawaii

Kaneohe Station, Hawaii

Maunawili, Hawaii

Chicago, Illinois

Baton Rouge, Louisiana

Saint Francisville, Louisiana

Crofton, Maryland

Medford, New Jersey

Pequannock, New Jersey

Deposit, New York

Madison, Ohio

Pittsburgh, Pennsylvania

Ladys Island, South Carolina

Austin, Texas

Huntsville, Texas

Muscoda, Wisconsin

Port Edwards, Wisconsin

Verona, Wisconsin

show all

Gardeners' Notes:


On Jul 5, 2004, NatureWalker from New York & Terrell, TX (Zone 8b) wrote:

Sunlight: full sun or part shade. Prefers warm weather. In very hot climates, prefers part shade.

Special locations: outdoor containers, xeriscapes.

Special characteristics: deer resistant, non-aggressive, non-invasive, & native to North America - Mexico

How to plant: Propagate by seed - Start seeds indoors 6 to 8 weeks before last frost, do not cover seeds, as they need light to germinate.

Germination temperature: 70 F to 75 F
Days to emergence: 5 to 10
Ease-of-care: easy.
Maintenance and care: Pinch back plants to keep rounded and bushy, deadhead to keep in flower.

Pests: Spider mites, Whitefly .

Susceptable Diseases:
Parasitic nematodes
P... read more


On Jul 4, 2004, punaheledp from Kailua, HI (Zone 11) wrote:

height on seed packet says 30" and mine have grown that tall, but want to lean to ground rather than stand upright. branches will grow upright off any branch that goes over sideways. I do not find folliage attractive, tends to curl inward, maybe something wrong with them. I would call color "periwinkle" lavender/blue, the plants saving grace. The flowers look almost fluorescent in the late afternoon/early evening light. OK if something is planted in front of them to hide folliage. I will probably not buy again.


On Mar 29, 2004, SILady from Enterprise, FL (Zone 9b) wrote:

Zone 9b - This has been a no care plant for me. Blooms year round with minimal care. I love it! It spreads and stays low. Looks really good with pinks. SILady


On Jan 22, 2003, poppysue from Westbrook, ME (Zone 5a) wrote:

Something about the tall ageratums that I prefer over the short bedding types. 'Blue Horizon' is a great cultivar. It blooms all summer, makes great cut flowers, and the butterflies LOVE it. It grows 16-18 inches tall and is a wonderful garden plant. It's seeds are sterile so don't bother collecting them... buy from a reliable source.