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Ageratum houstonianum is often confused with:
Conoclinium coelestinum Flowers
Liatris scariosa Form in bloom
Plants that fill a similar niche:
Catharanthus roseus Catharanthis roseus
Petunia x hybrida Petunia x hybrida
Salvia rosmarinus Rosmarinus officinalis
Ageratum houstonianum has some common insect problems:
Whiteflies Found on Flowers and Foliage
Aphids Found on Flowers and Foliage
Ageratum houstonianum has some common disease problems:
Southern Bacterial Wilt on Herbaceous Ornamental Plants

Ageratum houstonianum

Phonetic Spelling
a-ger-AE-tum ho-stone-ee-AE-num
Description

A frost-tender herbaceous annual to 1/2-1' tall, mounding with clusters of fluffy, aster-like flowers that should be planted with 10-12 inches of space.  Genus name comes from the Greek "a" meaning not and "geras" meaning old age because the flowers hold their color for a long time. 

Forms clumping mounds with colors of pink, white & blue from May through October. Dependable flowering annual. Confused with ageratums that are perennials with tall, erect stems and leaves well-spaced out, but similar in appearance with leaves and flowers. 

This plant is moderately drought tolerance but prefers rich, moist, well-drained soil as well as full sun. It is good for beds and containers, blooming from spring to frost.  Taller varieties make good cut flowers. This plant is seldom damaged by rabbits and deer. Used for edging or low massing plant in bed. Relative pest/disease free

Insect Pests, Diseases, and Other Plant Problems: susceptible to powdery mildew. Some cultivars have shown excellent resistance to phytophthora. See Phytophthora Root and Crown Rot in the Landscape.

Family name Asteraceae (Compositae)

Quick ID Hints:

  • Mounded herb as wide as tall, often 6"
  • Terminal cluster of small heads
  • Flowers all tubular, tassel-like
See this plant in the following landscape:
Japanese Shade Garden
Cultivars / Varieties:
  • 'Blue Danube'
    Excellent resistance to phytophthora.
  • 'Blue Horizon'
    Excellent resistance to phytophthora.
  • 'Leilani Blue'
  • 'Neptune Blue'
  • 'Redtop'
  • 'Summer Stars'
  • 'True Blue'
'Blue Danube', 'Blue Horizon', 'Leilani Blue', 'Neptune Blue', 'Redtop', 'Summer Stars', 'True Blue'
Tags:
#full sun tolerant#drought tolerant#summer annual#white flowers#pink flowers#blue flowers#rabbit resistant#summer flowers#deer resistant#bedding plants#cutting garden#pollinator plant#fantz#butterfly friendly#partial shade tolerant#container plant#annual#wildlife friendly#cpp
 
Cultivars / Varieties:
  • 'Blue Danube'
    Excellent resistance to phytophthora.
  • 'Blue Horizon'
    Excellent resistance to phytophthora.
  • 'Leilani Blue'
  • 'Neptune Blue'
  • 'Redtop'
  • 'Summer Stars'
  • 'True Blue'
'Blue Danube', 'Blue Horizon', 'Leilani Blue', 'Neptune Blue', 'Redtop', 'Summer Stars', 'True Blue'
Tags:
#full sun tolerant#drought tolerant#summer annual#white flowers#pink flowers#blue flowers#rabbit resistant#summer flowers#deer resistant#bedding plants#cutting garden#pollinator plant#fantz#butterfly friendly#partial shade tolerant#container plant#annual#wildlife friendly#cpp
  • Attributes:
    Genus:
    Ageratum
    Species:
    houstonianum
    Family:
    Asteraceae
    Life Cycle:
    Annual
    Country Or Region Of Origin:
    Central America
    Wildlife Value:
    Plant is seldom damaged by deer or rabbits and attracts butterflies.
    Play Value:
    Wildlife Food Source
    Particularly Resistant To (Insects/Diseases/Other Problems):
    Rabbits, deer, and drought. Some cultivars resistant to phytophthora.
    Dimensions:
    Height: 0 ft. 6 in. - 1 ft. 0 in.
    Width: 0 ft. 10 in. - 1 ft. 0 in.
  • Whole Plant Traits:
    Plant Type:
    Annual
    Woody Plant Leaf Characteristics:
    Deciduous
    Growth Rate:
    Medium
  • Cultural Conditions:
    Light:
    Full sun (6 or more hours of direct sunlight a day)
    Partial Shade (Direct sunlight only part of the day, 2-6 hours)
    Soil Texture:
    High Organic Matter
    Soil Drainage:
    Good Drainage
    Moist
    Available Space To Plant:
    Less than 12 inches
    USDA Plant Hardiness Zone:
    2a, 2b, 3a, 3b, 4a, 4b, 5a, 5b, 6a, 6b, 7a, 7b, 8a, 8b, 9a, 9b, 10a, 10b, 11a, 11b
  • Fruit:
    Fruit Type:
    Achene
    Fruit Description:
    Fruit is a cypsela which is a type of achene.
  • Flowers:
    Flower Color:
    Blue
    Pink
    White
    Flower Inflorescence:
    Cyme
    Flower Value To Gardener:
    Good Cut
    Showy
    Flower Bloom Time:
    Fall
    Summer
    Flower Shape:
    Tubular
    Flower Size:
    < 1 inch
    Flower Description:
    Fluffy, aster-like flowers that grow in clusters. Most commonly blue but can be pink or white. Terminal in clustered cymose heads; heads 1/4" diameter; Involucral bracts imbricated in several series. Lavendar, blue to pink, or white, tubular with 5 small lobes; pistils exerted, styles forked.
  • Leaves:
    Woody Plant Leaf Characteristics:
    Deciduous
    Leaf Color:
    Green
    Leaf Type:
    Simple
    Leaf Arrangement:
    Opposite
    Leaf Shape:
    Cordate
    Deltoid
    Obtuse
    Ovate
    Leaf Margin:
    Crenate
    Hairs Present:
    Yes
    Leaf Description:
    Alternate, ovate to deltoid, pilose on both sides to slightly downy, obtuse, cordate, crenate.
  • Stem:
    Stem Color:
    Green
    Red/Burgundy
    Stem Is Aromatic:
    No
    Stem Description:
    Semidecumbent, sometimes branched, green to reddish.
  • Landscape:
    Landscape Location:
    Container
    Landscape Theme:
    Butterfly Garden
    Drought Tolerant Garden
    Pollinator Garden
    Attracts:
    Butterflies
    Pollinators
    Resistance To Challenges:
    Deer
    Drought
    Rabbits
    Problems:
    Weedy