Growing Guide
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Annual Flower

Also known as Flossflower
Ageratum houstonianum
Asteraceae Family
Synonym: A. mexicanum

One of the few annuals to tolerate light shade, the most commonly used varieties are dense, rounded border plants providing a touch of rare blue to the garden setting. They are so compact and floriferous that they are often used in formal designs that need a blue color. Some varieties are white or pink, and few are tall with a loose form. Its fringed, button-like flowers are very unique and provide interesting texture.

Site Characteristics
  • full sun
  • part shade
Prefers warm weather. In very hot climates, prefers part shade.

Special locations:

  • outdoor containers
  • xeriscapes
Plant Traits

Lifecycle: annual

Ease-of-care: easy

Height: 0.5 to 2 feet

Spread: 0.5 to 1 feet

Bloom time:

  • mid-summer
  • late summer
  • early fall
  • mid-fall

Flower color:

  • blue
  • white
  • pink

Foliage color: medium green

Foliage texture: medium


  • cushion, mound or clump
  • loose and formless

Shape in flower: same as above

The small (1/4-inch), tufted flowers are clustered in dense, rounded heads about 1 inch in diameter.

Special Considerations
Special characteristics:
  • deer resistant
  • non-aggressive
  • non-invasive
  • native to North America - Mexico
  • butterflies
Special uses:
  • cut flowers - Only the taller varieties, not the dwarf bedding varieties.
Growing Information
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

Maintenance and care:
Pinch back plants to keep rounded and bushy, deadhead to keep in flower.

More growing information: How to Grow Annuals

Spider mites
Parasitic nematodes
Powdery mildew
Root rot
Various shades of pink and blue are available, as are dwarf plants which only grow to about 6 inches tall

‘Southern Cross’ is suited for containers in part shade.

‘Hawaii’ Series flowers in shades of blue, white or pink. Very popular series.

‘Bavaria’ has white flowers with bright turquoise borders. Grows to 1 foot tall.

‘Red Top’has very striking vivid magenta flowers on 3-inch heads. 2 to 2.5 feet tall.

'Blue Danube' is a classic hybrid with purple-blue flowers in dense heads. Compact and reliable garden performer.

‘Pinky Improved’ has showy flowers that are dark pink in the centers, fading to pale pink at their fringed edges. Compact and showy.

‘Southern Cross’ has bicolor flowers are white in the center, gradually turning to cornflower blue near the edge. Compact and showy.