Boxwood (Buxus spp.) is a dense evergreen shrub that is commonly used as a hedge or screen. Some species, such as American boxwood (Buxus sempervirens), a species hardy in U.S. Department of Agriculture plant hardiness zones 5 to 8, can get quite large, reaching heights of up to 20 feet at maturity. Other species and varieties remain much smaller, however, making them suitable for locations in the garden where a more understated presence is required.
English boxwood (Buxus sempervirens 'Suffruticosa'), sometimes called true dwarf boxwood, is the boxwood cultivar most commonly grown in the United States; it is hardy in USDA zones 5 to 8. It is a slow grower, often adding only an inch of height per year, and it rarely reaches a mature height of more than 3 feet.
Other small cultivars of American boxwood include 'Elegantissima,' which also grows to about 3 feet in height, and 'Jensen,' which may remain under 2 feet high. These two cultivars are hardy in USDA zones 6 to 8.
Varieties of small-leaved boxwood (Buxus microphylla) generally have leaves that are about an inch long; leaves of the American boxwood are typically about 1 1/2 inches long. Many small-leaved cultivars are very small in stature and are good choices for low formal hedges.
The 'Compacta' cultivar, also sometimes called 'Kingsville Dwarf,' is the smallest boxwood variety. It grows very slowly, adding about 1/2 inch in height each year, and reaches a mature height of about a foot. Its leaves, at 1/2 inch long, are exceptionally small, too. It is hardy in USDA zones 6 to 8.
Other dwarf small-leaved varieties include 'Morris Dwarf' (Buxus microphylla var. japonica 'Morris Dwarf') and 'Morris Midget' (Buxus microphylla var. japonica 'Morris Midget'), both of which reach a mature height of about a foot. These cultivars are also winter hardy in USDA zones 6 to 8.
Some varieties of Korean boxwood (Buxus sinica) also work well as low hedges. 'Nana' (Buxus sinica var. insularis 'Nana') remains about a foot high, but it spreads to width of about 3 feet; it is hardy in USDA zones 6 to 8. 'Wintergreen' (Buxus sinica var. insularis 'Wintergreen') is hardier than many other varieties; it can survive winters in USDA zones 4 to 8, and it is better than other varieties at retaining its green color throughout the year.