Evergreens tend to be backdrop plants in the landscape, while the flowering trees, shrubs and perennials hog the stage. But in winter, evergreens have a quiet majesty — especially when dusted with snow.
Among the most distinctive evergreens are the boxwoods, which have long been used to provide structure in formal gardens. Boxwood’s finely-textured foliage and tolerance for intensive pruning, makes it an ideal plant for creating a low to medium-height hedge. Unfortunately, boxwoods are hardy only to zone 6, so for northern gardeners they have not been part of our plant palette. Thanks to intensive breeding efforts there are now a number of new cultivars that thrive in zone 4 temperatures (-30 to -20F).
Leonard Perry, of the University of Vermont, recently pointed out that the boxwoods have earned a Cary Award in 2009, which is sure to raise the plant’s profile. The Cary Award is a program to promote outstanding plants for New England gardens.
Perry notes that most of the more hardy selections for northern gardens (zone 4) are selections of the Korean boxwood (Buxus sinica var. insularis), formerly known by a different scientific name (Buxus microphylla var. koreana), or hybrids of this and the southern common boxwood (B. sempervirens). Here are some of his favorites:
- Green Gem: Perhaps the lowest-growing, slowly reaching 2 feet tall and wide.
- Green Velvet: Forms a slightly taller globe shape (3 feet).
- Green Mountain: Taller yet, forming a pyramid 5 feet or more tall, and half as wide.
- Verdant Hills: A slow-growing introduction from the University of Vermont about 30 years ago. It is quite hardy (zone 3), and reaches 3 feet tall and about twice as wide.
- Chicagoland Green: This new variety comes from the Chicagoland Grows program of the Chicago Botanic Garden. It’s similar to Green Velvet, but faster growing What’s more, it has excellent, dark-green winter color.
- Wintergreen: Another cultivar of the Korean boxwood with good green winter leaf color. Perry says good winter leaf color is important when choosing plants because some selections of hardy boxwoods “bronze” or turn brownish yellow from winter sun and winds.
In the north, these hardy boxwoods grow in full sun to part shade. New plantings may benefit from shade until established. To keep leaves from bronzing in winter, plant in protected sites or use burlap screens. Like most shrubs, boxwoods prefer moist, well-drained soils.