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The Shady Border: Manipulating Light Levels
by Judy Springer
If you have the opportunity to garden beneath the shelter and shade of mature trees, you are lucky indeed. The very trees that produce shade will also provide privacy, structure, and year-round interest. They moderate temperature and light, creating a protected site, a restful sanctuary where you can watch changing light patterns alter the appearance of the landscape. In a shady border, there is less weeding than in sun, and gardening in comfort is possible, even on a hot summer day. Finally, shade gardeners get the chance to grow a wonderful selection of plants that require less than full sun.
While a bit of cover from the sun can definitely be an advantage, gardening in a dense wood is also a challenge. It's not hard to figure out why very little grows in deep shade. A high, impenetrable canopy can block out so much light that ground-level plants cannot photosynthesize successfully—so they can't survive, much less thrive. Mature trees are so good at absorbing available water and nutrients that little is left over for smaller plants.
Fortunately, not all shade is the kind that starves out smaller plants: Shade can range from light to deep; it can be dark and unbroken, or dappled; it can be cast by plants or man-made structures. Some types of shade provide much better growing conditions than others; the best kinds of shade for growing the widest range of plants fall in the middle ranges, and are often described as light to medium, partial, or dappled shade.
Plants grow well and look the best in "light shade"—about half a day of sun and half a day of shade. If you have morning sun and afternoon shade, most plants described in catalogs as "good for shade" will grow beautifully for you. It is in these brighter shady situations that "shade-tolerant" plants produce a good flush of foliage and the best flowering display. (If you have morning shade and intense afternoon sun, the same plants may look stressed or burned, particularly in the South.) But nature is always working against gardeners with light shade. Trees and shrubs are constantly gaining stature and girth, blotting out the sun and threatening to reduce light to unsatisfactory levels.
Cutting your way to bright shade
The key to a great border under a canopy of trees lies in the judicious use of chainsaw, pole pruner, hand saw, loppers, and hand pruners. Use these to let enough sunlight into your garden so that the plants grow well yet the unique benefits of shade remain. Many plants that will merely survive in medium to heavy shade will thrive if light levels are increased.
To brighten up your garden, start by removing damaged, unhealthy, or ugly trees, or those that have dense surface roots such as those of beech, birch, and red maple. Next, remove saplings that don't have enough space to grow, and then remove or limb up enough of the remaining trees to achieve varying degrees of light to medium shade throughout your garden. Then go back again and thin out any understory trees, brush, or shrubs that block light without making a real contribution to the attractiveness of the site.
Turning a sunny, barren spot into a shady border requires more patience. When developing this kind of site, use a variety of trees, evergreen and deciduous, that will eventually provide the desired shade, and serve as good "bones" for a new garden. Select trees and shrubs that don't produce heavy surface roots such as oaks, hickory, and other nut trees. Avoid most maples. Small trees such as Japanese maples, dogwoods, redbuds, and pawpaw are easy to work under because their roots are deep. Look for plants that display unusual spring or fall color, that flower or fruit unusually early or late, or that have evergreen foliage, interesting bark, or good silhouettes, and shape them to suit the space as they mature.
Stagger the heights of individual plants in the canopy. If you have closely planted trees of equal height, almost no light will penetrate, but if you use plants of varying heights, sunlight can penetrate clear to the woodland floor and provide the dappled, changing patterns that are most desirable in a shady setting.
The right plants for each low-light site
Shade gardening can be tricky in that it is sometimes difficult to tell just how much sunlight a particular spot in a shady area gets. Don't be afraid to move plants that aren't growing well. Watch plants closely, and if they look stressed by too much light, move them to deeper shade. If they look weak or spindly, move them to a brighter spot, or to the edge of the shady area. If you can't find the right spot for a plant, compost it and try something else.
Shade gardeners must provide the moisture and fertilizer a heavy planting of trees and shrubs demands, and then even more for the garden underneath. Since tree and shrub root systems are much more extensive than those of annuals and perennials, they will absorb what they need, leaving their less aggressive plant partners to get by as best they can. To ensure sufficient moisture for all your plants, make sure that watering remains easy as your garden matures. Install hose bibs, sprinklers, overhead watering, semi-permanent hoses, or leaky pipes wherever possible; whatever money you put toward easy watering will be money well spent.
Shade gardens in the city
If you are an urban gardener working with shade produced by nearby buildings, you cannot change existing light levels, but by carefully analyzing your exposure and hours of light and shade, you can choose plants that are best suited to your conditions. In some cases, reflected light from nearby buildings can be highly beneficial: It may produce higher light levels than you anticipate, and help plants grow more evenly because they don't have to stretch for light. As in other shade gardens, be sure to have a variety of pruning tools on hand, because plants growing in lower light need constant pruning and shaping to keep them from getting leggy and sparse as they reach for any available light.
Whatever you do, don't give up on your shady areas just because they require slightly different strategies from those you are most familiar with. The rewards of shade gardening will grow on you, I promise.
Judy Springer started gardening at age seven, and currently gardens on a 2.5-acre lot in a heavily wooded residential area in northern Virgina, primarily in a shaded woodland setting.