Not every plant can be a rock star; some must provide background vocals or adjust the lighting. Boxwood shrubs (Buxus spp.) are rarely given a leading role in a garden, but their compact evergreen foliage proves versatile and invaluable for hedges and boundaries. Tolerant and forgiving, boxwood grow in U.S. Department of Agriculture plant hardiness zones 6 to 9 in a wide variety of well-draining soils. Many boxwood lose the green in their foliage in the winter, turning off-shades of brown and orange, only to regain their natural hue the following spring. Other boxwood plants brown because their cultural needs are not being met. Your job as gardener is to figure out which scenario applies to your plants.
Record your shrub's progress on your calendar if you are not already familiar with the pattern of the foliage discoloration. If the foliage turns bronze or brownish-orange in the winter and then regains a healthy green in the spring, your plant is not in danger. Plant neighboring shrubs to offer shade or wind protection if the annual color change troubles you.
Look for small black dots on dead leaves if the boxwood remains discolored into summer. The plant may be suffering from "boxwood decline," a term describing a complex of diseases resulting from improper planting or care, If you find black dots, signaling infection by fungi in the genus Macrophoma, shake each stem of the plant thoroughly to remove loose, discolored leaves from the plant. Rake them up and burn them to prevent fungal spores from spreading.
Inspect your boxwood branches in warm, humid weather for orange-pink fruiting structures on the branches; these indicate infection by another fungus, of the genus Volutella, causing foliage discoloration. Remove and burn all infected branches. Disinfect your garden clippers before clipping and between cuts by wiping them with a rag soaked in denatured alcohol.
Thin your boxwoods to control Macrophoma and Volutella fungi. Cut back each smaller branch by about 6 inches to expose the shrub's branch structure. The fungi attack boxwood shrubs that have compacted, moist inner foliage, a condition that results from shearing the plants. Thinning boxwood without shearing it improves the air circulation inside the branches and allows the inner foliage to dry more quickly. Shearing entails scissor-cutting the entire boxwood, which crimps the ends and prompts undesirable inward growth.
Dig deep holes in the soil around your boxwood and fill them with shredded hardwood bark if the entire plant's growth appears stunted and discolored. This kind of over-all browning is likely caused by the root-rot fungi Paecilomyces and Phytophthora, and your best best is to improve soil drainage. Transplanting the shrub to well-drained soil is another option.
Things You Will Need
- Garden clippers
- Denatured alcohol
- Shredded hardwood bark
- One disease that discolors boxwood requires destruction of the plant. It is called boxwood blight. Caused by the fungus Cylindrocladium pseudonaviculatum, boxwood blight results in discolored foliage and streaked stems. The discoloration begins as brown spots in a circular pattern on leaves and branches. This disease won't kill the plant but it leaves it leafless. No cure exists yet, so be attentive for signs of the disease when buying new plants. Avoid overhead water and sterilize garden tools to prevent transmission of boxwood blight to healthy shrubs.
- Avoid planting boxwood in soil that is very acidic, compacted or poorly drained.
- Medioimages/Photodisc/Photodisc/Getty Images