Ageratum — Ageratum known as Whiteweed is a genus of about 60 tropical American herbs, annuals and perennials from the Sunflower family Asteraceae, tribe Eupatorieae.
They form tussocks or small hills. They grow to a height of 75 cm. The opposite leaves are cordate or oval, hairy or tomentose. The margins are slightly toothed or serrate. The leaves form compact clusters.
The fluffy flowers are lavender-blue, pink, lilac, or white; and spread in small compound umbels.
They give small, dry fruits.
They are grown for their flowers, especially the Flossflower (Ageratum houstonianum). Many are useful for bedding and bordering or in rock gardens.
Most common ageratums, “Hawaii” for example, are a short 6-8 inches when full grown. Tall ageratum are also available in seed catalogues, but rarely in retail stores. They are about 18 inches in height with blue flowers. There is also a medium height snowcapped variety, white top on blue flowers. The blues are most popular and common, but colors also include violet, pink and white. Their size and color makes Ageratum good candidates for rock gardens, flower beds, and containers.
Ageratum grow well in the sun or partial shade, from early summer to first frost. They are quite easy to grow, producing a profusion of fluffy flowers all season long. They are excellent for beginner gardeners.