Scientific: Ageratum houstonianum
Common: floss flower
Family: Asteraceae
Origin: Mexico

Pronounciation: A-ger-A-tum Hou-STON-i-an-um

Hardiness zones
Sunset
All
USDA All

Landscape Use: Floral accent where the color blue is desired in garden borders or as an edging plant, cool season bedding plant in Phoenix, warm season annual in the eastern United States, and a short-lived landscape perennial along the west coast; great for container gardens.

Form & Character: Short, diminutive perennial mostly treated as an annual in the landscape.

Growth Habit: Medium growth rate to 6 to 24 inches tall. Most cultivars form a dense mound.

Foliage/Texture: Small, opposite, light green leaves, ovate to 1 inch long, crenate margins; medium fine texture.

Flowers & Fruits: Terminal clusters of 1/4 to 1/2 inch flower heads in cymose clusters without ray flowers. Flower colors range from white, pink, burgundy, blue, mauve, and purple, fruit inconspicuous.

Seasonal Color: Anytime in bloom

Temperature: Optimal cardinal temperature range is 40o to 85oF.

Light: Full sun

Soil: Well drained and organic. Easily becomes chlorotic in sandy soils.

Watering: Regular

Pruning: None except to remove spent flowers.

Propagation: Seed which germinate in 5 days, cutting.

Disease and pests: Red spider mites, white fly, powdery mildew and botrytis on flowers.

Additional comments: "Ageratum" means not growing old (referring to it's persistent flowers), though the day of its popularity in Phoenix as a winter bedding plant seems to have 'died' several years ago. Facts are that floss flower is not as popular a bedding plant as it once in the middle and later 20th century. "Houstonianum" is named after botanist Dr. W. Houston who brought floss flower plants back from Mexico and the West Indies. There are many named cultivars with flower colors rangin from powder blue and white to mauve and deep blue and from pink lavender to deep burgundy red. Floss flower takes 600 to 100 days after germination to bloom. Plant out in late September in Phoenix for winter show.