Site Carefully

Most boxwood species are native to forest understory locations or protected valleys and hillsides, where they grow on loose, relatively dry soil. While boxwood can do well in many soil types, the siting of your plants to replicate the protection of its natural habitat is important.

Hardy in USDA zones 6 to 9 (occasionally colder), 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. Dolomitic lime (calcium carbonate or calcium magnesium carbonate), with its low oxide content, will maintain an elevated soil pH for longer period of time than quicklime (calcium and magnesium oxides) or slaked lime (calcium and magnesium hydroxides). If you don't know the pH of your soil, you can have it tested in the lab of your county's cooperative extension office.

Plant Carefully

Boxwood is an evergreen shrub and will continue to take up 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.

To plant, dig a hole 2 to 3 times as wide as the shrub's root ball and the same depth. When planting, give each plant some room for sunlight and good air circulation. Do not plant where other root systems will be in competition.

If the shrub is "balled and burlapped", place the root ball in the hole and cut the twine wrapped around the trunk. Roll the burlap off the root ball so that it lies flat in the hole and remove the burlap without damaging the root ball. The top of the root ball should be slightly higher than the ground level. Heavy shrubs usually settle once they are planted and watered. It's better to plant your boxwood too high than too low.

Shrubs purchased in containers should be removed from their pots. Roots should be inspected. If the plant is pot-bound, tease the roots free of the compacted shape. Plant container shrubs at the same height they have been planted in their pot.

Protect shallow roots

Boxwood plants have shallow and delicate roots. Do not locate other plants too close to the shrubs or disturb the roots with foot-traffic or edging of beds.

Mulch

After planting, apply an inch of composted bark chips or any suitable, permeable, organic mulch. The mulch will help retain moisture in the ground and maintain the cool, moist conditions needed at the roots. Remember not to mulch up to the base of the shrub or you'll create a damp environment that is an open invitation to pests and disease and a growing space for above-ground roots.

Remove the layer of mulch in the spring and replace it with fresh mulch, over moistened soil, once the earth has warmed up. Gently tidy and re-mulch in the fall after the soil has completely frozen through, as a layer of insulation.

Prune, Shear and Thin at the right time

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, around March 15. 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. Use clippings for propagation or holiday decoration if desired.

Landscape value

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.

For more information on boxwood care, selection and disease, see our Guide to Boxwood.

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