If your boxwood shrub's (Buxus spp.) dense, glossy-green leaves -- the ones that make different kinds of boxwood such go-to choices for shady spots in U.S. Department of Agriculture plant hardiness zones 4 through 8 -- decide it's time for a color change, don't despair. Boxwood leaves turns orange for two reasons, one seasonal and one disease-related, but the disturbing switch is limited to a handful of varieties.
Winter burn, or bronzing, commonly afflicts littleleaf and Japanese boxwoods (Buxus microphylla, Buxus microphylla var. japonica), hardy in USDA zones 6 through 9. The condition strikes plants receiving too much winter sun, especially when they're unprotected from frost or strong wind. The leaves may become orange, yellow or reddish brown.
Prevent winter burn with these methods:
- Plant Japanese and littleleaf boxwood where taller evergreens provide winter shade and protection.
- Water regularly, beginning when the new leaves emerge in spring and continuing until the ground freezes in winter. Boxwood needs 1 inch of rain or supplemental water per week. That's about 6 gallons per 10 square feet of soil.
- Insulate the root zone in fall with a moisture-retaining, 2- to 3-inch layer of organic mulch such as compost or shredded hardwood bark.
- Drape boxwood in burlap or bed sheets when frost or strong wind is likely. Remove the protection after the threat is gone.
- Replace burn-susceptible boxwood with resistant hybrid cultivars, such as 'Green Velvet' (Buxus 'Green Velvet'), hardy in USDA zones 5 through 8.
The good news is winter burn lasts only until the emergence of normal green leaves in spring.
Volutella canker targets the dwarf English boxwood cultivar 'Suffruticosa' (Buxus sempervirens 'Suffruticosa'), hardy in USDA zones 5 through 8. Dying leaves change to orange, then tan and finally straw-yellow. The disease is most active in warm, wet weather. Prune infected branches with by-pass pruners, and rake up dead leaves from around the plants. Disinfect the pruners in rubbing alcohol between cuts and dispose of the debris in sealed plastic bags.
To prevent infection, thin the outer canopy by about 10 percent each year in early winter. By opening the interior to light and air, thinning discourages infection.
Hold the pruners in one hand and reach into the plant to grasp a stem with the other. Grasp it anywhere from 2 to 8 inches below the outer leaves, depending on the size of the boxwood.
Snip the stem off, leaving at least one set of leaves for the sake of appearance.
Moisten a clean rag in rubbing alcohol and wipe the pruners' blades to to disinfect them before making the next cut
Work your way around the plant, pruning branches over the entire surface until 10 percent are thinned. Disinfect the pruners after each cut.
Dispose of the cut branches in plastic yard bags.