In the Garden:
New England
January, 2012
Regional Report

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Green Mound boxwood adds winter interest and shrugs off the Vermont weather in my garden. (That's inkberry, another hardy broadleaf evergreen, on the right.)

Thinking Inside the Boxwoods

Boxwoods are among my favorite shrubs. Which may seem at first like a rather hopeless fancy for a northern New England gardener. After all, it's in warmer climes than mine that boxwood really grows in all its glory. But while I may not be able to grow the great billowing hedges of common boxwood seen in places like England and Virginia, I can still enjoy the shiny, deep green, fine-textured foliage of the hardier littleleaf boxwoods and their hybrids.

Their botanical naming can be a little confusing. Littleleaf boxwood is Buxus microphylla. Japanese boxwood is B. microphylla var. japonica. Korean boxwood was formerly callled B. microphylla var. koreana, but is now properly called B. sinica var. insularis. You may find it offered for sale under either name, or sometimes just B. sinica. Common boxwood is Buxus sempervirens. English boxwood is B. sempervirens 'Suffruticosa'.

Choosing Beauty and Hardiness
One of my favorite hardy boxwoods is 'Green Mound'. This cross between Korean and common boxwood forms a mound of finely textured dark green foliage that has grown in my garden over the course of about fifteen years into a perfect oval about 4 feet tall and wide with only an occasional snip from my pruners. Rated as hardy to zone 4, 'Green Mound' retains its lovely color all winter long. Sited in a southeastern exposure along the front of my house, it has never suffered from winter injury. My only concern is when a heavy snowfall weighs down the branches, so I am assiduous about going out right after a storm and carefully brushing the snow off all my boxwoods. (Yes, I play favorites. My other evergreens usually have to fend for themselves!)

For a shrub with a more upright form, I've also planted the hybrid 'Green Mountain', which forms a pyramidal oval that will eventually grow to 5 feet tall and 3 feet wide. And to echo the larger form of 'Green Mound', I've planted 'Green Velvet', another hybrid which makes a tight, rounded mound reaching only 2 to 3 feet tall and wide.

These cultivars are also hardy to Zone 4. Other cultivars that are well suited to the colder parts of our region include the hybrids Chicagoland Green ('Glencoe') and 'Green Gem', and the Korean boxwoods 'Winter Gem' and 'Wintergreen'. Gardeners in the "banana belt" of southern New England states have even more choices, including common boxwood (Buxus sempervirens ) and its many cultivars, most of which are hardy to Zone 6, with some cultivars hardy to Zone 5.

Trouble on the Horizon
It is never good news that a heretofore unknown disease is rearing its ugly head in your area, but unfortunately for New England boxwoods, that's what has happened. In October of 2011, boxwood blight (Cylindrocladium pseudonaviculatum) was positively identified in Connecticut and was found at almost the same time in North Carolina and Virginia as well; this December it was also found in Massachusetts. This is the first time this fungal disease has been found in the U.S. It was first seen in the U.K. in the early 1990s and has now been reported throughout Europe, as well as New Zealand.

Infection starts as dark or light brown spots on the leaves, often with a dark border. The spots enlarge and blend together and the leaves turn brown or straw colored, giving the entire plant a "blighted" look. Soon after, the plant often drops its leaves. Stems may also be infected, causing distinctive angular, diamond-shaped dark brown to black lesions. As the lesions girdle the stems, the shrub dies back above the points of infection. The blight can spread rapidly when the weather is warm and humid, weakening and even killing plants, especially young plants or new transplants.

Although it has been reported on all members of the Buxus genus, certain species and cultivars seem to be especially susceptible to the blight. Common boxwood (Buxus sempervirens) and its cultivars, especially English boxwood (B. sempervirens 'Suffruticosa'), seem to be especially vulnerable to infection. But it is also a threat to the hardier littleleaf, Japanese, and Korean boxwoods and hybrids that are so useful in colder areas like mine.

Stealthy Spread
The sticky spores that spread boxwood blight can be disseminated over short distances by wind and rain, even farther by animals, birds, and by gardeners on contaminated clothes, shoes, and equipment. But it's thought that over long distances, boxwood blight is unintentionally spread by infected nursery plants that have few or no outward symptoms, perhaps as a result of fungicide treatments that suppress but don't eradicate the fungus.

So, especially if you are planting new boxwoods this spring, it is important to become familiar with blight symptoms and check plants regularly for the beginning signs of a problem. As of now, boxwood blight has only been found in Connecticut and Massachusetts in our region, but it is probable that it will spread to other New England states in time.

For more information on this disease, along with color photos to aid in identification, check out this publication from Connecticut Extension at http://www.ct.gov/caes/lib/caes/documents/publications/fact_sheets/plant_pathology_and_ecology/boxwood_blight-_a_new_disease_for_connecticut_and_the_u.s.__12-08-11.pdf. There are other diseases and problems that can be confused with boxwood blight, which this publication can help you identify. If you think you see signs of the disease, contact your local Extension Service for a confirmed diagnosis and advice on treatments.

And when growing any boxwoods, use cultural techniques that lessen the likelihood of fungal infections: space plants so that they have good air circulation around their foliage; avoid overhead watering; and clean up and dispose of fallen leaves from the plants -- don't compost any that appear infected.


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