Snowball spirea (Spirea nipponica), more commonly called “Snowmound,” features clusters of snowy white blooms that persist through early spring. The short, 2- to 4-foot tall shrub attracts butterflies and other beneficial insects to your yard. It also provides a living border plant well suited for fence rows or foundation plantings. Spirea grows in U.S. Department of Agriculture plant hardiness zones 3 through 8. It requires moderate annual pruning to produce ample blooms while retaining the best shape and health.
Disinfect your pruning shears with household bleach or rubbing alcohol prior to use to prevent transmission of disease organisms.
Thin out one-third of the older, larger stems in spring or early summer, immediately after flowering. Trim these back to the base of the plant using bypass shears or a small handheld pruning saw.
Prune back the remaining shrub by up to half its height to control the size and shape of the spirea. Cut each branch within ¼ inch of a leaf so bare stems are not poking out of the shrub.
Trim off any remaining dead flower clusters after pruning to improve the appearance of the spirea, especially if you don't cut back the entire shrub after thinning. Cut off the clusters above the topmost leaf.
Cut back the spirea in late winter before it resumes growth only if it's badly damaged or overgrown, removing the stems to the ground. Winter pruning prevents the spirea from flowering that spring, but it will recover and put on fuller, healthier growth over summer that results in good flowering the following year.