Boxwoods as landscape plants have long been a favorite of Southern gardeners. Boxwoods were planted on historic estates, such as Middleton Place in Charleston, which has grand formal gardens that include American boxwood (Buxus sempervirens). Boxwood owes its popularity not only to tradition, but also to its many landscape uses. Two species, American boxwood (B. sempervirens) and littleleaf boxwood (B. microphylla), and cultivars of these, are grown as ornamentals.
Common or American boxwood (B. sempervirens) is a wide-spreading shrub or small tree with dense, evergreen foliage. Plants grow to a height of 10 to 15 feet. The leaves are dark green above and yellow-green beneath, oblong to oval in shape and about an inch long.
Littleleaf or Japanese boxwood (B. microphylla) is a low-growing, evergreen shrub, which only reaches a height of 4 feet and a spread of 4 feet. Leaves are bright green, usually ¼ to 1 inch long and lance-shaped.
Both species grow at a relatively slow rate of less than 12 inches per year. American boxwood and most of its cultivars are tolerant of cold weather. Littleleaf boxwood and its cultivars are heat-tolerant.
Boxwood can be used in many ways because of its many and varied forms such as prostrate, globe, half-erect, weeping, columnar and pyramidal. There are also interesting variations in size and foliage. Some of the ways boxwoods can be used are as foundation plantings; to separate or screen areas; to provide background for other plantings; to provide a framework of a formal garden; to outline a terrace, walkway or parking area; for planter boxes; and as topiary pieces.
Boxwoods are adapted to a wide range of light conditions. They tolerate heavy shade but will grow in full sun if the roots are in a good soil environment. Boxwoods should only be planted in well-drained soils. Never plant them near downspouts or in any area that stays wet. They are extremely shallow-rooted plants and should not be planted too deep. The top 1/8 of the root ball ought to be above the existing soil level. Deep planting will usually cause loss of plant vigor and sometimes plant death.
Thorough watering encourages development of a healthy root system. Properly watered plants will be more firmly anchored in the soil and less susceptible to drought and nutritional stress.
To maintain vigorous plants, add 2 to 3 inches of organic mulch over the soil surface. Mulching not only keeps the shallow roots cool, but also conserves water by minimizing evaporation of moisture from the soil. Mulch also reduces weed problems.
There is no regular fertilization schedule for boxwoods. The most reliable guide to applying fertilizer is by testing the soil. A soil analysis by the Agricultural Service Lab at Clemson University will provide appropriate fertilizer recommendations for a specific site. For more information, refer to HGIC 1652, Soil Testing. If the boxwood begins to show symptoms of nitrogen deficiency, then it may be time to fertilize. The earliest symptom of nitrogen deficiency is yellowing of lower leaves. It will have a rather uniform yellowing that is more pronounced on the older leaves inside the plant. The leaves then become smaller and thinner and turn quite bronze in winter. Boxwoods may turn brown in winter as a result of winter injury also. Boxwood leaves will normally stay on the plant for three years. If they fall off earlier, this may be a symptom of nitrogen deficiency.
In early spring, broadcast fertilizer around the base of the plant, just beyond the drip line. Fertilizer particles that come into direct contact with the roots of unmulched boxwoods can cause root burn. If the fertilizer is over-applied, this will cause the leaves to turn brown and may result in dead branches. Established boxwoods should be watered thoroughly at intervals if rainfall is less than an inch per week. Broadleaved plants like boxwood lose water through their leaves during winter too.
Slow-growing, evergreen shrubs, like boxwoods, have the majority of their growth from buds near the ends of the branches. Some develop a dense outer shell of foliage with only a few leaves in the center. Thinning is a type of pruning that reduces the number of branches at the outer edge of the shrub. Preferably, this should be done annually. Thinning can be done anytime when the temperature is above freezing. Thinning is the single most important maintenance activity for keeping English boxwood (B. sempervirens ‘Suffruticosa’) healthy. Without adequate light or air circulation, the interior leaves die, with few leaves on the ends of the branches. Thinning will allow the center of the plant to receive sun and air. Much of the poor health of boxwood is a result of not thinning the plant. Very thick foliage encourages fungal leaf spot diseases and twig blight.
Boxwoods may be sheared to encourage additional branch development and to maintain a desired shape. The best time to shear the plants is in early June. Do not shear boxwood in late summer since this may force new growth, which will not have sufficient time to harden before frost.
To restore overgrown boxwoods or to control their growth, they need to be cut back. This is best done in early winter. If a small amount is to be cut, the entire pruning can be done at one time. If a more severe pruning is needed, then a two-step approach is best. First cut large branches on just one side of the plant. The second year, the other half of the plant would be pruned in the same manner.
Boxwoods are susceptible to many insects and diseases including boxwood leaf miner, boxwood psyllid, boxwood mite, foliage and twig blights, and Phytophthora root rot. More information on these problems may be obtained from HGIC 2052, Boxwood Diseases & Insect Pests.
Cultivars & Varieties
Buxus microphylla cultivars:
- ‘Compacta’or ‘Kingsville Dwarf’ is a very low-growing (1 foot), wide-spreading shrub with dense green foliage.
- ‘Wintergreen’ is a low, slow-growing, winter hardy shrub, which retains a nice green color all winter.
- var. japonica is a slow-growing evergreen, which grows to a height of 3 to 4 feet.
- var. koreana is a loose, open-growing shrub. It is very hardy, but the foliage turns brown in winter.
Buxus sempervirens cultivars:
- ‘Angustifolia’ has the largest leaves and is treelike in habit.
- ‘Argenteo-variegata’ has green leaves variegated with white.
- ‘Aureo-variegata’ has green leaves variegated with yellow.
- ‘Bullata’ is a low shrub with dark green, blunt leaves.
- ‘Handsworthiensis’ is a wide, strong-growing, upright shrub with dark green leaves that makes a very good hedge plant.
- ‘Northland’ is a wide spreading plant with dark green foliage. It is a hardy cultivar.
- ‘Suffructicosa’ is a slow-growing, compact, dwarf shrub. It is one of the most popular cultivars.