Ageratum Houstonianum for Monarch Butterflies

Ageratum houstonianum common names: Blue Horizon, Floss Flower, Mexican Paintbrush ‘Blue Horizon’

Ageratum Houstonianum Plant Specs

• Herbaceous perennial flower for USDA hardiness zones 9a-11b (lows -6.7° C or 20° F)
• Native plant to Central and South America
• Fast growing annual ageratum, but reseeds perennially in our northern garden
• Full sun to light shade
• Height: 1.5 to 3 ft feet
• Spacing: 1 to 2 feet
• Disk Flowers
• Flower color: light purple, violet, blue-purple, red, white
• Leaves: opposite, wide, heart-shaped
• Stems: thin, upright, bendable
• Blooms summer through first frost (Jul, Aug, Sep, Oct)

Floss Flower Pros

• Long flowering period- monarchs seek this out all season
• Care-free plant
• grows quickly from seed and reseeds
• Favorite nectar source of monarchs
• Provides migration energy for masses of monarchs

Floss Flower Cons

• Can be invasive with seeding and underground rhizomes, but easy to pull
• Blue Horizon floss flower spreads by excessive seeding
• Flowers aren’t showy
• Susceptible to White Flies and Powdery Mildew

Looking for an ageratum perennial better-suited for southern states? Try migration favorite Conoclinium greggii (Gregg’s mistflower)

Floss Flower Plant Propagation

• Sow seeds directly in fall or spring
• Root division in fall or spring
• Start seeds indoors with cold moist stratification

Mexican Ageratum Growing Tips

• In Minnesota, we pull our ‘blue horizon’ floss flower plants in the fall and let them come back from seed the next season.
• Good option moist meadows and wildflower gardens…will grow in clay soils

Pollinator Plus

Ageratum houstonianum also attracts bees, moths, painted ladies, skippers, and queen butterflies.

Buy Ageratum Houstonianum Plants and Seeds

As difficult as the botanical name is to spell and say, always purchase plants searching for this name. Common names are more often misused when labeling plants, so you’ll have best results searching for:

1. Find Ageratum houstonianum ‘blue horizon’ on Etsy (rarely available…look specifically for A. houstonianum ‘blue horizon’….other varieties rarely attract butterflies)

2. Ageratum houstonianum ‘monarch magic’ ⬅️ (compact variety that is also a proven monarch magnet)

If you’re interested in adding more butterfly plants to your garden, check out our butterfly flowers page