Shade: definitions
rich, varied...and elusive
As much as we recognize that sunshine is the engine that drives many plants to lush flowers and useful fruits, we all seem to savor on summer days, the comfort of shade, especially that cast by very large and graceful trees. These, of course, are plants capable of great height to grow in full sun, but for us they become graceful umbrellas.
It is here, in the shade, that we find the air a bit cooler, perhaps a bit less turbulent, and the intensity of light a bit easier on the eyes. While many of us savor the exuberance of a sunny meadow or the bounty of a field of vegetables, we save a special fondness for the serenity and tranquility of the woodland and its shade. Some anthropologists, in fact, advance the theory that taking comfort in the forest is more ingrained that we might wish to admit, that early man was vulnerable on the savannah to big animals of prey (including his own kind), and that the great forests of the world offered a place in which to hide from those who would do him harm.
Just as we might find shelter under the canopy, so, too, do many species of plants. These species take in brief moments of light to grow, but also take full advantage of the cooler air, oftentimes more moist soil, and almost always the rich earth that comes from large volumes of compost and duff.
Rhododenron maximum enjoys the shade of deciduous forests, especially those of an acidic, well trained and even somewhat dry nature. It's usually found where there is morning sunshine.
Yet in this rich symphony of green, there are many individuals and each has a particular taste in the amount of sunlight and even the times of day it arrives and departs. In our native woodland plant gardens, the seemingly simple issue of shade becomes vexing with a dizzying array of adjectives. Light, open, high open, part, dappled, full, dense, woodland, medium, half, moderate, morning, afternoon, cold, north wall, deep, heavy and more litter informative books like autumn leaves, bogging us down in a mat of confusion. The authors use the expressions, but spend little time defining precisely what they mean.
Our tour of sunlight - or lack thereof - begins where there's little dispute. Full sun means just that: unobstructed sunshine from dawn to sunset. If an hour or two is deducted because of trees or other obstructions, it's simply sun. It doesn't matter if it's a swamp, moist meadow, dry field, alpine location or lakeshore.
These varied sorts of locations provide us with clues about the inexact terms applied to shade. Perhaps the pair that confounds us most is "part shade" and "part sun." Both suggest sunlight for about half the day, but when we examine in detail the kinds of plants connected with each, we discover that "part shade" really means morning sunshine and shelter from the stronger rays of afternoon. And "part sun" applies best to species that can do without the gentler sunshine of daybreak but relish a strong dose from noontime until nearly evening.
We find the answers by comparing multiple sources of habitat information on a particular species. For example, one expert might display a half-sun/half-shade icon next to the name, indicating that it grows in a partial sunshine location; another might say "part shade" and yet another might advise "prefers afternoon shade" and another "woods edges." Eventually a fairly reliable pattern evolves for us, and as we sift through companion plants we can reach a conclusion.
Pools of light slither across the woodland garden, sometimes larger, sometimes smaller and all in patterns to be exploited by the shade gardener
We discover a similar pattern with dappled sunlight, the sort that is sunshine filtered through a high canopy of trees to create moving pools of light on the forest floor.
These are usually "open woods," but "high shade, as well as "medium shade" and "filtered sunlight" may also depend on the size of the pools and the time of day it passes across the plants below. It's important to some, but not all, species, and here experience is the best instructor. For example, Anemone virginiana is most commonly mentioned in the "open woods" context and for the most part thrives in dappled shade. But if there's a strong burst of sunlight at midday, we see the plants droop in dismay, only to revive once the torment has passed. Soil moisture can be an important factor, especially in afternoon light. If wetter, it will help cool plants in the strong sunshine and help with transpiration rates.
Yet several authors hasten to add that soil moisture and the specifics of topography can dramatically impact habitat suitability for many species of plants, pointing to those with preferences to north or south slopes, location relative to the crest of a hill, or shelter in low pockets.
The dappled light that slips through leave of deciduous trees is often ideal for many woodland ephemerals, who take advantage of full sun in the very early spring to reward us with a rich display of dainty flowers. As the leaves fill out, the new shade protects delicate plants from too much sun and they thrive in the sort of light that we often characterize as the most attractive shade of all.
We find Actaea americana in cool, rich, shady locations, mostly dappled shade but also leaning toward part shade
As we continue to study preferred habitats of native plants, we come across those who are fond of gentle locations in coniferous forests (deep shade) or perhaps in thickets (part shade or part sun, depending on the angle of the sun) or in clearings (part sun, but at midday).
Our exploration inevitably takes us to a crucial point when designing a woodland garden, especially when using native plants. The preferred habitat, gleaned from as many sources as possible, defines the organization of the garden after a careful review of the site itself. While this process can be tedious, our reward will be a species list that works as well as a good appreciation for the variables in nature and why all are precious.
Summing up, then definitions of "shade" vary widely, as do illustrations and counsel on the many terms available. But some clarity is possible, although we would do well to be sensitive to ranges of light and prepared to experiment with plant locations to find the most suitable, given soil moisture, topography, and regional climate conditions.
All other things being equal the range of light for most species of plants, light to dark, would appear be:
- Full Sun -- unobstructed sunlight, all day long.
- Sun - eight hours of direct sunlight, or lots of sunshine through loose canopy
- Part sun - half a day or a bit more of sunlight, or afternoon sunlight
- Part shade - half a day or a bit less of sunlight, or morning sunlight
- Dappled shade - moving pools of light through the tree canopy, with the density of the canopy impacting pool size
- Full shade - continuous shade all day, except perhaps for a brief period of sunlight in the morning or afternoon
- Dense shade - deep shade found under conifers or from sides of buildings
Resources
Schenk, G. (1984). The Complete Shade Gardener. Boston: Houghton Mifflin Company.
Sperka, M. (1973). Growing Wildflowers, A Gardener's Guide. New York: Charles Scribner's Sons.
Mooberry, F. (1993). Gardening in the Shade in Woodland Gardens - Shade Gets Chic. Brooklyn: Brooklyn Botanic Garden,
Druse, K. (1992). The Natural Shade Garden, New York: Clarkson N. Potter, Inc., New York, 1992
Schmid, W. (2002). An Encyclopedia of Shade Perennials. Portland: Timber Press.
Zeman, A. (1992). Shade Gardening, Burpee American Gardening Series. New York: Prentice Hall Gardening.