Ageratum houstonianum, also called Blueweed, Bluemink, Floss flower or Pussyfoot, is a member of the Asteraceae family and is native to Mexico, where it is also known as the Mexican paintbrush.
Gardeners adore it because of the beauty of its blue flowers and how long they last. They appear in June and last until frost.
Ageratum houstonianum - flossflower photograph by Carl Lewis.
Ageratum is also prized because of is great range. It thrives in hardiness zone 2 all the way down to hardiness zone 11.
It is a marvelous plant to grow in beds, in rock gardens, or at the edges of herbaceous borders and walkways. It is also a good container plant.
Ageratum is an annual, which means it only lasts a season. It takes easily to rich and average soils, so long as it is well-drained.
It is a good idea to keep the soil a bit moist because the plant droops if the soil becomes too dry.
Floss flower growing in the wild showing a scruffier nature than garden cultivars,image by Forest and Kim Starr; CC.
The plant loves full sun though it can also flourish in partial shade. In a very hot climate, Ageratum does best with some afternoon shade.
Ageratum houstonianum can be grown easily from seed, though the seeds are tiny and need to be handled with some care.
The seeds can be started indoors before the last frost date, or they can be sown into the ground after the danger of frost is over.
For longer lasting blooms, it is best to gat a head start and start the plants indoors, and transplant out when the soil is warm.
Close up of Ageratum houstonianum flowers photograph by Forest and Kim Starr; CC.
Ageratum houstonianum is a popular plant found in nurseries and garden centers. Plant the taller varieties about a foot apart (30 cm) and the smaller ones about a half a foot (15 cm) apart.
Floss Flowers in their native habitat (wastelands, Roadsides), photograph by John Tann; CC.