Evergreen trees and shrubs, stalwart garden companions, hold their greenery the year around. Although alike in this respect, evergreens vary in many other ways. Some have fine-needled foliage or bold leaves in various shades of green. Others offer unusual cones, gleaming berries, or colorful blossoms.
Although attractive in their own right, one of the greatest garden assets offered by evergreens is their ability to screen unsightly views. Both evergreen shrubs and trees can provide year-round privacy, blocking unwelcome views or viewers. They also make effective — and beautiful — windbreaks and snow fences.
Where winters are cold, evergreens are often limited by the harsh climate; there they are all the more valued for their winter greenery, a welcome contrast to bare-limbed deciduous plants. In warmer climates evergreens, particularly broadleaf kinds, abound. However, be careful not to use too many evergreen trees close to the house. In overabundance they have a somber effect, and block welcome sunshine, especially in winter.
Unfortunately, many evergreens need pruning to stay within the size and scale of most home landscapes. Properly pruned, these plants will remain handsome for decades.
Despite their dependability for hiding, screening, softening, and backdropping, not all evergreens are forgiving of and responsive to pruning. It is important to know when and how to prune to achieve good results.
Evergreens can be rounded, oval, pyramidal, upright, horizontal, weeping, or irregular. The natural branching pattern of the plant dictates its shape. By respecting this inherent form when pruning it is possible to limit the size of an evergreen without changing its shape. Not only does this preserve the plant’s true beauty, but it saves the expense of replacing overgrown plants.
Evergreen shrubs are often sheared into individual geometrical forms to create a formal shape and to slow the plant’s growth. Altering a natural plant shape by shearing commits the gardener to spending more time and energy in maintaining the sheared form than if the natural shape had been respected.
Although shearing does limit size to some extent, a sheared evergreen gradually grows larger over the years because shearing removes only part of the previous season’s growth. Sheared shrubs will eventually outgrow their space, while those that are pruned by thinning can usually be kept at the desired size.
There are three basic kinds of evergreens: needled or needleleaf, narrowleaf, and broadleaf.
Needled and Narrowleaf Evergreens
The vast majority of needled and narrowleaf evergreens aren’t flowering plants, but produce naked seeds borne in woody or fleshy cones; scientists refer to them as gymnosperms, a classification containing many plant families. Many important landscape evergreens, such as pine, spruce, fir, and hemlock, produce their seeds in woody cones and belong to a plant grouping called conifers.
The foliage on needled evergreens may be flat-sided as in fir, square as in spruce, or triangular as in pine. Other conifers, such as juniper, are narrowleaf evergreens with flat needlelike leaves or scales pressed against the stem. They have fleshy cones resembling berries.
In contrast, broadleaf evergreens, such as rhododendrons, holly, boxwood, laurel, Indian hawthorn, and euonymus, bear flat leaves similar to those of deciduous plants — except that the foliage remains green the year around. They are a diverse group of plants whose foliage may actually be fine-, medium-, or coarse-textured and come in various shapes and sizes.
Broadleaf evergreens are angiosperms or flowering plants; the flowers may be showy, as on rhododendrons, or inconspicuous, as on holly.
Growth Patterns of Evergreens
Most needled and broadleaf evergreens send out a single flush of growth each year in spring. After this growth matures in midsummer, the plant develops new terminal buds, which remain dormant until the following year.
Needled evergreens start growing each spring from these buds initiated during the previous growing season. Most pines, for example, produce a single flush of growth from terminal buds on the end of every branch. This soft new growth, consisting of a flexible stem and developing bundles of needles, is called a candle. (Pines are easily recognized by their bundles of two, three, or five needles enclosed in a papery basal sheath.) Growth from the largest terminal bud becomes the new leader for that branch; smaller buds below the terminal become side branches.
This pattern of growth produces the whorled branching characteristic of needled evergreens. The age of a tree or branch can be determined by counting the number of whorls of side branches; each year a new whorl of growth is added. Some broadleaf evergreens grow in a similar manner. Rhododendrons, for example, produce a flush of succulent stems and leaves from buds located to the side of each flower bud. Dormant buds develop at the stem tips in midsummer and grow the next spring.