Japanese Boxwoods and Common Boxwoods are popular hedge plants. So what sets these two shrubs apart?
Japanese Boxwood (Buxus Microphylla var. Japonica) can cope with heavy frosts and is also able to take full sun. This gives it a distinct advantage over Common Boxwood (Buxus Sempervirans), which can suffer in freezing weather and full sun. Propagation of both varieties is by cuttings, and the weather-coping capabilities of the Japanese Boxwood means cuttings can be safely planted outdoors (even before the last frost).
The Japanese Boxwood is a compact and dense shrub that will grow to about eight feet tall and spread about six feet. The Common Boxwood also has dense growth, but can grow into a small tree, and can be up to 30 feet tall. It is unusual to see Common Boxwoods as tall as that in gardens, but this capability is often used to produce irregular profiles in hedges. Generally, neither Boxwood will be allowed to grow to its full potential.
The Japanese Boxwood thrives in alkaline soils. The Common Boxwood requires a rich, slightly acidic soil. The roots of the Japanese Boxwood go deeper than those of the Common Boxwood, which are often so shallow that they break the surface. In warm weather, the Common Boxwood needs to be watered regularly and benefits from a layer of mulch over the roots to help keep them moist.
Both Boxwoods produce tiny whitish flowers and small fruit. The flowers and fruit are of little value because neither Boxwood grows quickly from seed.
Both plants are evergreen, but the Common Boxwood is more affected by cold winds and the leaves can turn brown after exposure to a dry cold wind. In severe cases the leaves may fall and replacements will be slow to appear. This could adversely affect the shape of the shrub.
Boxwoods make excellent hedging plants, as they grow densely and can be cut to just about any shape. Both shrubs can be trained into particular growth patterns and can be trimmed regularly to maintain the shape. This makes them ideal for topiary work.
The Japanese Boxwood can cope well with light shade, but the Common Boxwood better copes with heavy shade, which makes it an ideal shrub for darker corners of a garden where little else will flourish. Both shrubs can be used in bonsai, but the slow growth means that many bonsai specimens must be allowed to grow in their natural style before they can be trained or clipped into the desired shape.
Neither shrub has particular problems from a gardening point of view. Both will establish themselves well, and will produce a very attractive hedge or garden highlight throughout the winter. Gardeners with sensitive skin should always wear gloves when pruning the Japanese Boxwood because the leaves contain steroidal alkaloids and exposure to the sap from the leaves or stems can cause skin irritation.
In reality, these two Boxwoods are interchangeable for most gardeners and will perform equally well. The only real difference of note is that the Common Boxwood can be allowed to grow into a tree to provide shade.
Expert gardening advisor Karen Thurber adds, "There are many cultivar and varieties of Boxwood. Some plants will only grow as tall as four feet over 50 years, while others may have a slightly different color, or be better suited for cold climates. Do some research before buying, to select the correct plant for your location."