A lot of people can't tell the difference between boxwood (Buxus spp.) and small-leaved hollies (Ilex spp.), especially Japanese holly (Ilex crenata). Both kinds of plants have small, dark green leaves, are evergreen and grow into compact shrubs that take pruning well. However, once you look more closely, it's easier to tell which is which.
The leaves on boxwood branches are arranged opposite from each other, making pairs. The leaves on holly occur alternately. While boxwood leaves always have smooth edges, holly leaves, even the small, oval ones, sometimes have tiny scallops along the edge. The leaves of holly usually are slightly darker green and shinier than those of boxwood.
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Both holly and boxwood flowers are tiny. Boxwood, which has both male and female flowers on the same plant, has chartreuse, star-shaped flowers but does not produce berries. The flowers grow in clusters with one female flower in the center, surrounded by male flowers with yellow anthers. Hollies have tiny white flowers and need a separate male and female plant for berries to occur on the female plant. If pollinated, Japanese holly produces small, blue-black berries.
Small-leaved hollies grow faster than boxwood, with a more rigid, branching habit. Most have a mounded habit, reaching 4 to 8 feet tall. "Sky Pencil" (Ilex crentata "Sky Pencil") is a narrow, upright cultivar that grows to 10 feet. Japanese hollies thrive in U.S. Department of Agriculture plant hardiness zones 6 though 9. Boxwood tends to grow in a rounded, compact form, although American boxwood (Buxus sempervirens) can reach 20 feet tall. English boxwood (Buxus sempervirens suffruticosa) is a slow-growing dwarf cultivar that reaches 3 feet. Little-leaf boxwood (Buxus microphylla), also a dwarf, has smaller leaves. Boxwood grows in USDA zones 5 through 9.
Both holly and boxwood thrive in acidic, well-drained soil in full or part sun. They both benefit from regular pruning, and boxwood takes shearing exceptionally well. Some boxwoods turn a copper color in winter, while hollies stay dark green. Both plants look best when protected from drying winter wind.