Pruning smooth hydrangea "Annabelle" (Hydrangea arborescens "Annabelle") encourages strong growth, helps prevent the spread of plant diseases and keeps the shrub looking tidy. Hardy in U.S. Department of Agriculture plant hardiness zones 3 through 9, "Annabelle" is a deciduous shrub that blooms for up to two months starting in early summer, and sometimes it also flowers in fall. "Annabelle" grows 3 to 5 feet tall and 4 to 6 feet wide, and its flowers form large, rounded clusters. Wipe pruning shear blades with a cloth that was dipped in rubbing alcohol before and after pruning "Annabelle."
Pruning in Winter
Late winter is the best time to prune smooth hydrangea "Annabelle" to promote vigorous growth the following growing season. In cold areas, "Annabelle" often dies to the ground during severe winters. Prune all the remaining stems just above the soil surface at the end of winter. Remove the pruned stems, dead leaves and other plant material, and put them in the trash to discourage the spread of pests and diseases.
Alternatively, leave "Annabelle" not pruned. When not trimmed, the shrub produces more and smaller blooms, which flop less in rain than larger blooms. "Annabelle" flowers on the current season's growth.
Pruning in Spring
A smooth hydrangea "Annabelle" shrub that is not pruned in winter needs pruning in spring to remove its weakened and damaged stems. Winter weather can damage stems, allowing diseases to enter the plant.
Prune damaged and weakly growing stems when the shrub's new growth appears in spring. Cut each damaged stem 3 to 4 inches below the damaged area, just above an outward-facing leaf bud. Weakly growing stems are thin and have few leaf buds, often with all the leaf buds growing at the stems' ends. Weak stems should be pruned to ground level.
Removing the old, fading blooms from smooth hydrangea "Annabelle" improves the shrub's appearance. Removing those spent flowers is called "deadheading." "Annabelle" flower heads turn lime-green and tan as they fade, and some gardeners dislike the appearance of the faded flowers. Prune fading blooms when more than one-third of the individual flowers in a flower cluster are tan. Prune at flower stems' bases, where those stems join the rest of the shrub.
Another option is to allow the faded flowers to remain on the shrub. In areas that experience frosts, the frosted flowers make a winter display.
Taking Cut Flowers
Smooth hydrangea "Annabelle" provides plentiful cut flowers for the home. If you want fresh, white blooms, then the best time to cut a flower cluster is when more than one-half of its individual flower buds are open. Prune at the desired stem length, and strip off all leaves that will be below water level in the vase that will hold the flowers.
Alternatively, cut flowers that faded to tan. "Annabelle" cut blooms that have faded don't need water. Tie the cut flowers' stems loosely with twine, and hang them upside down in a cool, airy place until the petals are dry and crispy. Then stand the dried flowers in a dry vase.