Gardeners prune plants to control their size, keep them healthy and spur new growth. Ornamental plants--which can be divided into woody ornamentals, ornamental shrubs and flowers--require annual care and pruning, though the time of pruning depends on the time of flowering. Prune spring-flowering ornamentals after they've bloomed in the early summer; prune ornamental flowers at the end of the flowering season; and prune summer-flowering ornamental shrubs and trees in the early spring.
Cut woody ornamental plants (such as clematis) in fall after they have flowered to a height of 18 to 24 inches. The woody ornamentals will regenerate in the spring.
Prune flowering shrubs (such as azalea) to rejuvenate. Remove up to 1/3 of the old growth from the plant in spring after frost danger passes. Trim back the ornamental shrub to shorten its branches if you feel it's grown too long.
Cut back perennial ornamental flowers in the late fall after they've finished blooming for the season. Trim them back at the base, leaving 4 inches of stem. In the spring, these ornamentals will regenerate.