“Anthony Waterer” Japanese spirea (Spiraea japonica “Anthony Waterer”) is a deciduous shrub with burgundy spring foliage, blue-green summer foliage and red fall foliage. In addition to colorful foliage, it produces showy, bright red flowers in the spring and summer. It grows to a height of 2 to 3 feet and width of 3 to 4 feet in U.S. Department of Agriculture plant hardiness zones 4 to 8. Even though these are smaller shrubs, a yearly pruning just before they begin putting on new growth in the spring will keep them looking their best.
Prune off damaged, diseased or dead branches with sharp pruners. Trim off any dead flowers that remain on the shrub from the previous summer. Remove branches that cross other branches. Prune out up to one-third of the old, thick branches if the shrub is older and looks too full or woody.
Take a step back and look at the shrub often while pruning to get a sense of what needs to be trimmed for the desired size and shape. Trim off an entire branch or side branch if it sticks out beyond the desired size and shape of the shrub.
Cut back all or a few of the remaining branches to reduce the shrub’s size. Trim them back to varying lengths to prevent a thick, full outer canopy with naked center branches. Make angled cuts 1/4-inch beyond a healthy growth bud. Cut above an upward-facing bud to encourage upright growth. Make the cut above a bud facing to the side to encourage more width.
Shear faded flowers off with hedge clippers at the end of summer to encourage another flush of flowers.
Prune off one-half of the remaining old, thick branches in the following year if the shrub is older and requires renewal. Prune off the remaining old, thick branches in the third year. Alternately, trim the entire shrub back to a height of 6 to 12 inches for total renewal. Pinch the tips off the new branches to encourage a fuller, more compact growth habit.