Boxwood decline is a condition that causes weak growth, discoloring of leaves, and branch dieback in boxwood shrubs. This condition usually involves several factors, including poor planting conditions and improper cultural practices, as well as stem and root diseases. Boxwood planted in a poor environment typically shows symptoms within a few years.
Although all boxwood varieties can be affected, boxwood decline mainly affects American and English boxwood shrubs.
Planting in a poor environment, combined with over-pruning, over-mulching, and improper watering, can lead to boxwood decline. Initial symptoms include an inner leaf shed, which can expose twiggy growth to infection from stem canker fungi. Excessive leaf drop then encourages shallow root systems that, in turn, become vulnerable to extremes in moisture and temperature. In moderate climates, certain microscopic worms (nematodes) can stress the plant, resulting in root damage and loss. Boxwood decline symptoms typically include weak, sparse, or spindly growth, yellow-orange discoloration of foliage, and premature leaf drop.
To prevent boxwood decline or improve affected plants, follow these horticultural practices: fertilize regularly to increase plant vigor; mulch lightly- about a two-inch depth, keeping mulch several inches away from trunk; water deeply during dry periods; and thin out dense center foliage annually to improve light and air circulation, and to help prevent inner defoliation and twig canker. It is easy to over-do-it when thinning boxwoods, for the best results contact your local arborist.