The ageratum, or Ageratum Houstonian, is an annual flower that is a member of the Asteraceae or aster family. These plants are native to a wide area of land that covers the southern part of Mexico, as well as the Pacific Coast side of Guatemala and parts of Belize on the Caribbean Sea. The flossflower or Mexican ageratum are other common names for this plant.
While native species of ageratum tend to grow to over 2 feet (60.96 cm) in height, individuals who wish to use plants in landscaping may prefer the more domesticated varieties grown in greenhouses and nurseries. These plants typically range from 6 to 12 inches (2.4 to 4.8cm) in height. They are also generally more compact and grow in smaller mounds.
Plants generally bloom from mid-June through October and produce clusters of fuzzy flowers in shades of purplish-blue, pink or lavender. The leaves of the ageratum may grow as long as 4 inches (10 cm) in length, though they generally only grow to about half of that size. These leaves grow oval- or heart-shaped.
When planting from seed, individuals should start the seeds in peat pots about 6 to 8 weeks before the final frost of the season. Once the danger of frost has passed, they may then transfer the seedlings outside for planting. Since plants are typically inexpensive to buy as young seedlings, however, many gardeners prefer to wait until the warmer weather arrives and purchase them already started in cell packs. This allows for the simplistic ease of transferring them directly into the garden.
Often used in container arrangements and rock gardens, ageratums also have a place in flower gardens as edgings and borders. They do well when mixed with other types of flowers and look quite striking when placed with flowers of complimentary colors. Individuals may wish to consider placing them with bright marigolds or other yellow flowers that will compliment their softer blue to purplish color.
These plants prefer full to part sun and a rich, moist, well-drained soil. They will still thrive, however, even when planted in the shade in average or poor soil. Although popular as a low-maintenance plant once started, ageratums do require supplemental water during periods of no rain. When planting ageratums, individuals should space plants 6 to 8 inches (15.24 to 20.32 cm) apart to allow for spreading. Plants are suited for United States Department of Agricultural (USDA) zones 5 through 10.