Overview: Buxus is a genus of about 70 species of evergreen shrubs and occasionally small trees found in habitats ranging from rocky hills to woodland in Europe, Asia, Africa and Central America. The leaves of many Buxus species are very small which is an ideal attribute for bonsai. In Spring, Buxus display a show of male flowers with conspicuous yellow anthers that surround single female flowers.
The two Buxus species that are commonly seen as Bonsai are Buxus microphylla/ Japanese Box and Buxus sempervirens/ Common Box. Outwardly both of these species are very similar, carrying elliptic, glossy, dark-green leaves to 2-3cm long. The main difference between B. sempervirens and B. microphylla is their vigour; B. sempervirens can reach eventual heights of 5metres with a spread of 5metres, B. microphylla on the other hand is very slow growing, only reaching an overall height of around 75cm with a 1.5metre spread.
There are a large number of varieties of both species available at nurseries though variegated varieties should be used with care as they are less suitable aesthetically.
Commonly seen in American based Bonsai magazines and websites is the variety Kingsville Box/ Buxus microphylla 'Compacta'. At present this variety would not seem to be available in Europe yet.
BONSAI CULTIVATION NOTES -
Position: Sun or shade. Excessive sunlight can result in sun-scolded leaves. Both species are fully hardy but frosts and cold winds can damage top growth. Protection from frost should be given as soon as temperatures threaten to drop below freezing to protect foliage It is common for the leaves of Buxus microphylla to bronze in cold Winters.
Box is regarded by some as suitable for indoor cultivation during the Winter and should be placed in an unheated room with good light. Ensure good air-circulation around the tree to avoid fungal diseases.
Feeding: Every two weeks throughout the growing season.
Repotting: Every 2 to 3 years in Spring as new leaf buds start to extend. Use a basic soil mix. Trees that are root-bound will grow very slowly indeed but with repotting will regain vigour.
Pruning: New growth needs to be continually trimmed to shape throughout the growing season. The natural habit of Buxus species is very angular and stiff, Buxus bonsai should be pruned and styled in a way that softens their form. Buxus are a broad-leaved species that suit deadwood styles and small amounts of jinning.
Propagation: Root semi-ripe cuttings in Summer. Division in early Spring. Air-layering in late-Spring.
Pests and Diseases: Red spider mite can be a problem in hot weather.
Box Blight: Box Blight is a fungal disease that has seriously affected many mature box plants in gardens across much of Europe in the past 4 or 5 years. Thought to be a 'new' disease and as yet has not be clearly identified. Box Blight infects the leaves causing spots that lead to rapid defoliation, it quickly moves into the stem tissue killing off smaller branches. Over a few weeks, black streaks appear on the bark and a grey-ish fungus may be seen under the remaining leaves. Within two or three months of infection the entire plant can die.
Box Blight is not only extremely virulent, it is capable of defoliating very mature plants in a matter of weeks. There is currently no available chemical remedies for this disease. Diseased branches affected by blight should be pruned off at once. To avoid spreading the disease to other Buxus plants, bin or burn infected branches, clean tools with meths, position affected trees in isolation and try to avoid contact with affected plants in damp weather.
