How to Use Ageratum Houstonianum

Plant ageratums in full sun in northern gardens. In the South and Southwest, where the sun is intense, plant them in afternoon shade. Use a hand trowel to dig a hole large enough for the root ball and gently spread the roots when planting. Give the plants an initial dose of flowering-plant fertilizer, water well and then spread 2 to 3 inches of mulch over the roots, being careful to keep the mulch 1 inch away from the crown of the plant. Deadhead spent flowers and fertilize regularly for flowers until frost.

Edge flower beds with smaller varieties by planting them 4 to 6 inches inside the planting bed's outer edge. Space the plants 6 inches apart. Good varieties for edging include Blue Danube, Blue Hawaii and Pink Improved.

Mass ageratum plants for a striking display in large landscapes. Space small plants on 6-inch centers, larger ones on 12-inch centers. Ageratums are especially effective when planted with yellow marigolds, silver-foliaged plants or pink begonias.

Plant taller varieties in the middle or back of mixed flower beds. Ageratums that grow 12 to 15 inches tall include Bavaria, with white flowers edged with turquoise, the blue Leilani and the purple and blue Artists series. Lohman's Frost grows 18 to 24 inches tall with blue flowers. Even taller are the 24- to 30-inch Red Top, with bright magenta-red flowers, Red Sea, 24 to 36 inches tall with red blooms, and Blue Horizon, also 24 to 36 inches in height but with medium-blue flowers.

Use ageratums in containers, either by themselves or in mixed plantings. The smaller varieties such as the white-and-blue bi-color Southern Cross are especially suited for shady containers. Give container-grown ageratums good potting soil, fertilize regularly and water whenever the top inch of the soil feels dry.

Add smaller cultivars of ageratum to rock gardens. Ageratums are native to Mexico and Central America, so they thrive in the reflected heat from the rocks. Give them supplemental watering during extended dry spells. (ref 5)

Cut taller varieties for use as filler plants in flower arrangements. Cut the flowers early in the morning while they're well-hydrated.