Pruning of boxwoods is done mainly to control size and shape, and to improve the health of the shrub. Annual thinning with hand shears is recognized as one of the best pruning methods for maintaining the health of the shrub. Happily, you can do this type of thinning in early winter when the trimmings can be used for holiday decorating!
Boxwood is one of the best of the broadleaf evergreens to use for holiday decorating because the leaves hold their rich green color well and remain fresh for a long time. In outside arrangements, the cool temperatures keep them fresh even without water! To cut boxwood greens for decorating, follow the procedures outlined below for annual thinning.
Annual thinning with hand shears is recommended to open up the plant and bring air, light, and water to the interior of the shrub. This type of pruning not only reduces the incidence of disease by increasing air circulation, it also rejuvenates the plant by stimulating the production of basal buds and new interior growth.
Shearing boxwood is not recommended because it stimulates growth only at the ends of the branches. Continual shearing causes the exterior of the shrub to become very dense and reduces the amount of light and air that reaches the interior of the shrub. This growth pattern is unhealthy for the plant as a whole because the lack of light and air circulation causes inner leaves to die and can also lead to an increase in disease. If you do shear your boxwood, be sure to also do some thinning afterwards to keep it from becoming too dense.
Severe pruning of overgrown boxwood should only be done in late winter or early spring when the boxwood is dormant. They can be pruned heavily until just bare branches remain or you can even cut them back to one to two feet above the ground. The boxwood in this photo taken in early April of 2009 had been cut back to about 15" from the ground in March of 2007. This type of severe pruning is not always 100% successful but a very high percentage do come back with beautiful new growth!
After severe pruning, fertilize your shrubs with Plant-tone, rock phosphate, and green sand according to the Viette's recommendations.