Ageratum (Ageratum houstonianum)

Ageratum (Ageratum houstonianum), an annual flower, is also known as Mexican Ageratum or Flossflower. This summer to fall flowering plant grows 4 to 24 inches tall and 8 to 24 inches wide depending on cultivar. The flower heads are small, about ¼ inch across, and may be white or varying shades of pink or blue. Pictured above is ‘Blue Danube’ that grows to about 7 inches tall.

Using ageratum in the landscape

Use ageratum as a border in front of other flowers, along a walkway, on a hillside or in planters. Choose a full sun to part shade location to plant ageratum. As an annual, ageratum should grow in most climates as well as most soil types. However, in hotter zones such as USDA 9 or further south, plant ageratum where it receives afternoon shade.

Planting ageratum

Cast seeds in late spring in USDA zones 8 and north. For USDA zones 9 and south, plant according to package directions, which may be late fall or early winter. Work the soil to a depth of at least 6 inches. Moisten the soil and spread the seeds. Lightly sprinkle dry soil over the seeds to hold them in place. Keep the soil moist. Sprouts appear in five to 10 days. Thin to about 12 inches apart. Pinch back the seedling when about 4 inches tall to encourage branching for fuller plants.

If planting from pots, loosen the soil to a depth to match the height of the container or 6 inches, whichever is deeper. Make an opening in the loosened soil to match the diameter of the plant container. Gently remove the plant from the container and place in the hole. Add or remove soil from the hole if necessary so the top of the root ball is level to the surrounding soil. Set multiple plants about 12 inches apart.


Spread 1 to 2 inches of mulch, such as pine chips or leaf mold, if desired. Mulch helps block weed growth and retains moisture. Water every seven to 10 days if there is no rainfall. A water-soluble fertilizer may be applied according to the manufacturer’s instructions.

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