Dwarf Kingsville Boxwood Care Guide
Buxus microphylla 'Compacta' is generally known in the bonsai world as the Kingsville Dwarf or Dwarf Kingsville. This species has an interesting history – some resources claim this plant as "Japanese", when in fact it originated in the Baltimore, MD area in the early 1900's. History's tale is that William Appleby discovered the seedling as a sport on a Korean Boxwood, back in 1912. It was released to the trade in 1937, and registered by Dr. Donald Wyman in 1963. It has since risen to popularity among enthusiasts and beginners alike. This tiny little boxwood does not grow past a foot tall or wide.
This widely sought-after cultivar is highly prized for its leathery, tiny leaves (about ¼"), dense growth habit, and rough, aged-looking bark which is so valued by bonsai growers. The branches are horizontal growers which gives the tree an even older appearance.
Boxwood enjoys being outdoors in summer and being protected from freezing in winter, ideally in a cool indoor or greenhouse environment with root protection. Alternatively they can be brought inside during winter.
Both droughts and prolonged rainy periods can cause damage to the Dwarf Kingsville.
This bonsai is tolerant of most light levels. Partial shade is ideal for outdoor plants. A breeze can help keep mildew on inner leaves at bay.
Buxus microphylla prefers moderate moisture conditions, and does not tolerate wet feet. Allow to dry a bit between thorough watering's, but make sure not to let it dry out completely. Daily misting helps keep the foliage green and healthy.
Boxwood plants do well with a balanced bonsai feed with supplemental iron. Fertilize bi-weekly during the growing season, from about May until October. Allow the plant to rest until after the winter solstice in late December. An application of pulverized organic fertilizer once during the growth period is beneficial.
Styles – the dense foliage on this boxwood make it suitable for many different shapes, as well as shohin and mame. It takes readily to root-over-rock and responds well to jin and shari.
Pruning should be carried out in spring. The slow growing nature of Dwarf Kingsville Boxwood makes it low maintenance and easy to shape. After branches have been exposed to the sun hard break-back will occur readily, facilitating development of foliage pads. Thin and pinch off most of the new undesirable growth in order to control shaping. Take care to minimize the removal of foliage though, as these are very slow growing at only a quarter of an inch to an inch annually.
Wiring may be performed on this tree, just do so with caution because the branches can be brittle. Copper wire allows you to sense when a branch is being bent too close to the breaking point. The boxwood assumes interesting shapes on its own so be sure to utilize those before making drastic changes, integrating them into your design.
This bonsai may be propagated by placing mature cuttings that have been treated with rooting hormone into a mixture of equal ratios sharp sand, perlite, and peat. The cuttings should be placed in the shade, preferably in a cool greenhouse environment in the fall. Water throughout winter and apply bottom heating for best results. Air layering can work well with larger specimens.
Dwarf Kingsville Boxwood typically only needs repotting every other year. This should be carried out in the spring. Group plantings may go as long as four to five years before being repotted. This species is very tolerant of aggressive root pruning, allowing up to half of the root mass to be removed. In warmer climates repotting may be done in summer or autumn, although it's best to refrain from doing so in the hottest months.
The soil should be well-drained and can be slightly alkaline. A low-acid soil designed for bonsai is best, along with an occasional application of lime. Fertilizer and iron may be added during the transplanting process, although it's not necessary. This plant prefers a pot on the deeper side.
Insects/Pests & Diseases
Boxwood may be affected by red spider mites, leaf miners, and various fungi, including rust. Washing the plant down will remove most pests. If evidence of fungus is noticed – curled or spotted leaves – remove infected leaves and treat with a mild fungicide.
Root rot can be a problem for this bonsai – if leaves begin to wilt or wither in the absence of a watering issue, the roots are usually the culprit. Examine the root system and remove any discolored, mushy, smelly, or otherwise "off" roots.
Examining your plant frequently for bugs and other health problems, paying close attention to proper watering and feeding, will help you keep the tree healthy and strong.