Japanese Boxwoods vs. Common Boxwoods

Japanese boxwoods are popular hedge plants, as are common boxwoods. So what sets these two shrubs apart?

Weather Tolerance

Japanese boxwood (buxus microphylla ssp. Japonica) will cope with quite 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. Propagation of both boxwoods is by cuttings and the weather-coping capabilities of the Japanese boxwood mean that cuttings can be safely planted outdoors even before the last frost.  

Growth Potential

The Japanese boxwood is a compact and dense shrub that will grow to about 8 feet tall and spread about 6 feet. The common boxwood also has dense growth but can grow into a small tree 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.

Soil Requirements

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.   

Flowering

Both boxwoods produce tiny whitish flowers and small fruit. The flowers and fruit are of little value because neither boxwood grows very quickly from seed.

Evergreen

Both plants are evergreen but the common boxwood is 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.

Uses

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 copes with quite 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.

Problems

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. 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.