How do I grow boxwood and which varieties are good for the Northeast?

Answer

For complete details of boxwood care, selection and problems, see our guide to Boxwood.

Boxwood (Buxus) is a versatile and useful evergreen shrub that can be planted as edging, hedge, screen and specimen plant. While consistently popular with gardeners and long-considered a reliable plant, boxwood is not without its problems. Much of the recent attention to the plant has focused on those shortcomings. Boxwood can be damaged by winter wind and sun, road salt, improper planting, pruning and irrigation, and a number of pests and diseases. In the last decade, boxwood blight has become a growing concern in our area. A fungal disease caused by Calonectria pseudonaviculata, boxwood blight affects all boxwood cultivars, though some are less susceptible than others.

Winter care, proper planting and timely pruning improve your chance of success and enjoyment of this plant. Poor siting and care are, in fact, the most common problems with growing boxwood and make the plant more susceptible to disease.

A number of insect pests, particularly boxwood leafminer, can be a problem and should be treated. English boxwood (Buxus sempervirens ‘Suffruticosa’) is susceptible to a fungal disease known as “boxwood decline." Again, healthy plants in a proper growing environment are less susceptible.

Growing boxwood

Boxwood will grow in full sun but prefers a slightly shaded location. Keep in mind that the shrubs will also need some shade in winter, when the leaves have fallen off deciduous trees and taller shrubs. Choosing a position with some shade, up to about 20 percent, will reduce both summer scald and winter injury risk. Shade also reduces the likelihood of mite damage. Exposure to strong winter winds should be avoided but air circulation around the plant is important in reducing the incidence of disease.

Soil should drain well, as boxwood won't tolerate waterlogged conditions. Additions of organic matter may be necessary and proper systems to enhance drainage may be needed. In areas with acid soil, lime should be added to raise the pH to 6.5 - 7.5.

Boxwood is an evergreen shrub and will continue to take up some nourishment from the soil through the colder months; it should be planted at a time of year that is less challenging for it to establish its root system, neither too hot nor too cold. Early fall (September) or spring (April) planting are best as long as the weather is cooperating and the warmest and coldest temperatures have passed.

Pruning boxwood

The preferred time to  prune boxwood  is late winter or early spring in the New York area, once the coldest plunges of temperature have passed. Boxwood takes to light cutting and shaping quite well but little is required other than to correct the shape by reducing a branch here and there. If you respect the natural shape of the plant you have chosen and prune simply to maintain tidiness, you will limit the potential for plant stress and die-back. Do not prune when the temperature is projected to be below 40°F for several weeks.

If you are regularly cutting most of the branch tips of your shrub and altering its natural shape significantly, that is considered shearing. June is best; do not risk die-back by shearing after mid-August. This type of reduction is the most stressful to the shrub and, for dense plant types, should be accompanied by thinning. Boxwoods do not reliably regenerate leaves from bare wood, so you need to restrict shearing to no more than ¾ of the way into the current exterior layer of leaves. The top of the plant should remain less wide than the lower branches so that sunlight can reach all parts.

Thinning to remove some of the branches at the outer edge of the plant is different from pruning or shearing, and particularly important for the dense common (American) and English boxwood types. Thick growth reduces sunlight into the center of the shrub, which causes foliage drop, weakening the plant. The resulting leaf debris accumulates in the lower branches, causing abundant and vigorous aerial roots to grow in this moist and dark environment. Eventually, the exposed aerial roots will die, shocking the weakened plant. Lack of air circulation will also promote disease if thinning is ignored.

Thin dense boxwoods from early spring to late fall if the foliage completely hides the view of the interior branches. Do not thin when extreme temperatures are predicted. To thin, using sharp bypass pruners, reach inside about 6 inches, and remove a twig. Continue to prune until the small interior twigs become intermittently visible, along with the older, light green interior leaves. When pruning is completed, the shape and size of the boxwood should look unchanged.

Preventing foliage diseases

Plant discoloration and decline, in whole or in part, is frequently a problem of care and environment but also may be disease-rooted. Careful cultivar selection can reduce the incidence of disease, particularly boxwood blight. Many consider common boxwood and English boxwood  to be the most attractive varieties for plant form and leaf but they are also the most disease-prone.

The Boxwood Society of America lists ten cultivars that, after evaluation by Dr. Kelly Ivors of North Carolina State University, proved to be less blight prone than other common cultivars evaluated. No English, American or Sheridan Hybrid boxwoods warranted inclusion on this list. It should be noted that plants that have shown greater disease resistance in one trial will not necessarily prove as resistant in another environment. Many gardeners are simply replacing boxwood with similar plants in their gardens. (A good list or replacement plants for the New York area, and their growing characteristics, suggested by the Cornell University Cooperative Extension can be found through this link.) 

While more is learned, careful cultivation of plants improves strength and disease resistance.

The Ivors list of cultivars includes mostly Asiatic cultivars belonging to B. microphylla (littleleaf boxwood) or B. sinica var. insularis (Korean boxwood), including

Buxus microphylla ‘Green Beauty’

Buxus sinica var. insularis 'Eseles' (Wedding Ring®)

Buxus sinica var. insularis ‘Wintergreen’

Buxus microphylla ‘Peergold’ (GOLDEN DREAM):

Buxus sinica var. insularis 'Winter Gem'

Buxus sinica var. insularis 'Nana'

Buxus sinica var. insularis 'Franklin’s Gem'

Buxus sinica var. insularis 'Wee Willie®'

Buxus harlandii 'Richard'

For additional information on each of these cultivars as well as attributes of Korean, littleleaf and Harland boxwood, important aspects of care and boxwood diseases, see our guide to Boxwood.

For tips on a variety of gardening topics, see our Plant Information Guides.
- Courtesy of NYBG Plant Information Service

 

  • Last Updated Mar 06, 2021
  • Views 4148
  • Answered By Leslie Coleman

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