Common Name: Japanese boxwood
Type: Broadleaf evergreen
Family: Buxaceae
Zone: 6 to 9
Height: 3.00 to 12.00 feet
Spread: 3.00 to 12.00 feet
Bloom Time: April to May
Bloom Description: Creamy white
Sun: Full sun to part shade
Water: Medium
Maintenance: Medium
Suggested Use: Hedge
Flower: Insignificant
Leaf: Evergreen
Other: Winter Interest
Tolerate: Rabbit, Deer
Culture
Best grown in evenly moist, well-drained loams (sand-clay mixture) in full sun to part shade. Plants thrive in part shade locations, including open sun-dappled conditions or light shade with several hours of morning sun or early afternoon sun. Plants can grow in close to full shade, but typically are less vigorous and more open with decreased foliage density. When grown in full sun, plant foliage is more likely to scorch, bronze in winter or suffer from mite attacks. Plants prefer soils with a pH of slightly acidic to slightly alkaline. Plants are generally tolerant of pruning and shearing as needed. Pruning should never be done prior to the last spring frost date. Pruning too early in spring often promotes tender new growth that may be damaged or killed by a late spring frost. Avoid cultivating around plants because they have shallow roots. Roots appreciate a good organic (e.g., bark or compost) mulch (1-2”). Thin plants and remove dead/damaged branches annually to improve air circulation. Boxwood is best sited in locations sheltered from strong winds, with, if possible, some protection from full winter sun. Winter winds can remove moisture from leaves at a rapid rate, often resulting in dehydration and bronzing. Foliage of Japanese boxwood will usually remain green in winter if grown in shady areas, but the foliage will usually turn reddish if grown in full sun. Good green color usually returns quickly by mid-spring. Plants may aggressively self-seed in optimum growing conditions. Plants are easily propagated by cuttings.
Noteworthy Characteristics
Buxus microphylla var. japonica, commonly called Japanese boxwood, is a broadleaf evergreen shrub that is native to certain mountainous areas in Japan, primarily on the islands of Shikoku and Kyushu. In comparison to other species of boxwood, it is a relatively fast-growing shrub (to 12" per year) that typically matures over time in a loose upright form to 6-8' tall with a spread to as much as 16' wide. Glossy rounded leaves to 1" long are variable in shape (ovate to obovate to elliptic). When grown in sun, leaves will begin to turn orange-red-bronze after first fall frost, but they quickly return to green in spring. Axillary and terminal panicles of apetalous, pale yellow flowers bloom in March. Flowers are inconspicuous. Branchlets are sharply quadrangular.
Genus name comes from the Latin name for plants in this genus.
Specific epithet means small-leaved.
Common name of boxwood is in reference to the prior use of the wood to make boxes. Another theory on common name is that boxwood describes the quadrangular (square box cross section) stems of young plants.
'National' is a Japanese boxwood cultivar introduced by the U.S. National Arboretum. It is an upright, fast-growing evergreen shrub which is typically seen growing as a 3-5' tall shrub. If left unpruned, however, it can eventually grow to 12' tall or more over a period of 25 years. Spring flowers are inconspicuous. Small, elliptic to obovate evergreen leaves.
Problems
Boxwoods can be somewhat temperamental plants to grow in the St. Louis area where the evergreen foliage tends to bronze (turn unattractive brownish-yellow) in harsh winters, particularly if plants are located in open areas where exposed to full sun and winter winds. No serious insect or disease problems. Some susceptibility to blights and leaf spot. Root rot can also be a problem in poorly-drained soils. Plants are susceptible to boxwood leafminer and boxwood mites, but are usually not affected by boxwood psyllid. Japanese boxwood is considered to have good resistance to nematodes.
Uses
Specimen or accent in the landscape. Also useful in shrub borders or foundation plantings. Edging. Hedge.