Growing and Saving the Seed of Ageratum

Latin name Ageratum houstonianum is an annual flower that is nicknamed "floss flower" for its thread-like appearance. Tufts of true blue color make this a popular landscaping flower. Beware that all parts of this plant are poisonous!



Native to southwestern North America and Central America, ageratum has long been a popular landscaping plant. Short varieties are planted at the front of the border, while tall varieties are excellent for cutting. Attractive to butterflies.


  • Ornamental, perfect for beds and borders and containers.
  • Butterfly garden.
  • An excellent cutting flower.
  • Attractive to pollinators like butterflies, wasps, and bees.



  • Seeds germinate in 7-10 days.
  • Direct sow seeds outdoors in spring, after last frost, or start indoors in trays 6-8 weeks before last frost.
  • Surface sow seeds uncovered, as they require light to germinate.
  • Ideal germination temperature is 65-75 F.


  • Plants are not cold hardy.
  • They prefer full sun, but will also grow well in part shade.
  • Rich, well-drained soil is best; however, plants are fairly tolerant of a wide range of soil.
  • Space plants at least 10 inches apart.
  • Do not allow plants to dry out, as they will experience drought stress.
  • Deadhead regularly in order to promote more blooms.


  • Mostly pest-free, with some experiencing powdery mildew or whitefly.
  • Avoid letting plants dry out; ageratum is not a drought-tolerant plant.


  • Harvest the flowers when the heads are spent.
  • Spread the flowers on screens to dry, then shake to remove the seeds.
  • Seeds remain viable for up to 4 years.