The Ageratum genus, a member of the Aster family, includes more than 40 annual and perennial plant species native to Central America and Mexico, but for North American gardeners, the name ageratum generally refers to Ageratum houstonianum, also known as floss flower. This annual plant is useful in flower beds for the large masses of bright purplish-blue flowers that bloom reliably from late spring until the first frosts of fall. Ageratum is a useful plant for lending long-lasting color in the mixed flower bed. Low-growing varieties are often used as edging plants or in rock gardens. Taller plants are a good addition to cutting gardens. Ageratum will do well in sunny locations planted in moist but well-drained soil that has been amended with compost or peat moss.