How to Prune Old Andromeda

Hardy in U.S. Department of Agriculture zones 5 to 8, andromeda (Andromeda japonica), or Japanese pieris, is a broadleaf evergreen shrub native to Asia that produces drooping clusters of white or pink flowers that are reminiscent of lily-of-the-valley. Pruning old andromeda bushes is necessary to keep the plant healthy and looking its best. Timing is key when it comes to Japanese andromeda pruning, as is having a clear idea of what you want to achieve.

Pruning is an important part of caring for any ornamental shrub, including andromeda. Without pruning, old growth can crowd out new growth. Pruning not only enhances flower production and appearance, it is also necessary to avoid diseases and keep pests at bay.

When pruning andromeda bushes, cut back old stems all the way down to the soil. Cut down new growth to half its size to encourage the development of side shoots. You may also want to thin crowded branches to let air and light in. Remove any dead flowers and stems as well.

Every three years, the Purdue University Extension recommends a heavy pruning to rejuvenate the andromeda bush. The University of Massachusetts Center for Agriculture, Food and the Environment says that you can also rejuvenate an overgrown andromeda plant gradually by removing 1/3 of old growth one year, 1/2 of old growth the next year and the remaining old growth a year after that.

Andromeda bushes flower in the spring, usually in April. Spring-flowering shrubs like andromeda set their buds for the following year during the summer months. You should deadhead and prune these types of bushes right after they are done flowering. If you prune andromeda bushes earlier than this, you may end up with no flowers that year, warns the Purdue University Extension, though the plant's long-term ability to flower will not be affected.

You also want to avoid pruning andromeda bushes in the fall, as this will reduce flowering the following spring if you remove any buds. However, the New York Botanical Garden says that fall pruning may be necessary if the plant has become too leggy. Do not prune andromeda during the summer, which can stress the plant. However, feel free to remove any dead or diseased growth at any time during the growing season.

You may need multiple tools in order to properly prune andromeda bushes. You can use hand shears for thin branches. However, branches that have become more 1 1/2 inches thick, which you are likely to encounter on old, overgrown andromeda bushes, require a pruning saw. Long-handled shears are ideal for branches with widths between 3/4 and 1 1/2 of an inch, reports the University of Massachusetts Center for Agriculture, Food and the Environment.

Keeping your cutting tools sharp and properly oiled will make the process of pruning andromeda easier. It is also important to clean your shears and pruning saws after every use. Wipe them using rubbing alcohol anytime that you remove diseased branches to prevent pathogens from spreading to other plants.