Photo by Melody

PlantFiles: Floss Flower, Ageratum
Ageratum houstonianum 'Blue Horizon'

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

2 vendors have this plant for sale.

6 members have or want this plant for trade.


12-18 in. (30-45 cm)

6-9 in. (15-22 cm)

Not Applicable

Sun Exposure:
Full Sun

Unknown - Tell us

Bloom Color:

Bloom Time:
Mid Summer
Late Summer/Early Fall


Other details:
This plant is attractive to bees, butterflies and/or birds
Flowers are fragrant
Average Water Needs; Water regularly; do not overwater

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

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By poppysue
Thumbnail #1 of Ageratum houstonianum by poppysue

By SILady
Thumbnail #2 of Ageratum houstonianum by SILady

By NatureWalker
Thumbnail #3 of Ageratum houstonianum by NatureWalker

By mgarr
Thumbnail #4 of Ageratum houstonianum by mgarr

By Calif_Sue
Thumbnail #5 of Ageratum houstonianum by Calif_Sue

By AnniesAnnuals
Thumbnail #6 of Ageratum houstonianum by AnniesAnnuals

By DaylilySLP
Thumbnail #7 of Ageratum houstonianum by DaylilySLP

There are a total of 10 photos.
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3 positives
1 neutral
No negatives

Gardeners' Notes:

Positive NatureWalker 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
Powdery mildew
Root rot

Neutral punaheledp 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.

Positive SILady 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

Positive poppysue 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.


This plant has been said to grow in the following regions:

Richmond, California
San Jose, California
Santa Maria, California
Deltona, Florida
Dunnellon, Florida
Fort Lauderdale, Florida
Kailua, 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

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