In addition to evergreen leaves that emerge with a red, pink or coppery hue in spring, the Japanese pieris (Pieris japonica) also produce attractive white flowers in late winter to mid-spring. Also called Japanese andromeda or lily-of-the-valley bush, this rounded shrub grows up to 5 to 10 feet tall and 6 to 12 feet wide, depending on cultivar and growing conditions. Grow it outdoors only where hardy, such as in U.S. Department of Agriculture plant hardiness zones 5b through 8. Pruning maintenance is generally minimal.
Pruning Time Frame
Schedule any annual maintenance pruning of Japanese pieris immediately after the flowering season ends. In USDA zone 8, flowering begins in late February to early March and winds down by April 1. Farther north, flowering is delayed until late March, with the season ending by mid to late April. Depending on latitude and elevation, pruning season ranges from early April to very early May. Do not prune in summer or fall, as you risk removing woody tissue that will produce flowers next year.
What to Prune
Healthy, established Japanese pieris shrubs rarely need pruning every year. The maintenance involves more scouting and trimming plants than major pruning work. Typically, only trim back branch shoots that spoil the attractive informal symmetry of the plant. If the shrub isn't too large, deadheading--the removal of old flower clusters--to remove the seed heads can make the Japanese pieris look a bit more attractive. Make pruning cuts 1/4 inch above a lower leaf or branch joint.
Winter Dieback Issues
After an unusually cold or dry winter, Japanese pieris shrubs may display dieback across parts or all of its leafy canopy. Do not prune to tidy up the plant over the winter, or early spring as flowering occurs. Wait until mid-spring, since any growth of new leaves emerges on seemingly dead branches then. This eliminates the apprehension about knowing which winter-damaged branches and twigs are dead, and which are still alive and regrow.
Pruning tasks involving Japanese pieris shrubs centre around trimming thin, tender twigs at the outer reaches of branches. Therefore sharp hand pruners suffices for equipment. To remove larger branches with a diameter greater than 3/4 inch that have died, use loppers. Do not paint or seal any wounds creating from pruning; the plant naturally calluses.