An Encyclopedia of Shade Perennials - Hardcover

Defining shade is more an art than a science: it is impossible to establish a permanent value for a given spot in the garden. Light levels vary, from morning to sunset, for sunny and cloudy days, and with the passing of the seasons. Theoretically, full shade is where direct rays of sunlight never reach. It is not, however, the total absence of light. Full shade requires a source of light to produce it, and in the case of gardens, it is the sunlight that causes it. Plants grow in full shade by utilizing reflected sunlight. I wanted to establish, to my mind at least, what full shade really means; I finally resolved that full shade must be on the north side of my house, where I had planted a bed of hostas. Direct sunlight never reaches into that corner, yet the hostas thrive, because the open corner receives plenty of reflected light. Many gardens have a similiar north-facing corner created by a permanent structure.

Full shade is modified by where it is produced. Because the summer sun is higher in the sky at Hosta Hill (in Tucker, Georgia, 34 degrees North latitude), the full shade cast by the north wall of my house is shorter than that in my mother's garden of Detroit, Michigan (42.5 degrees North latitude): Mother's house casts a longer field of full shade. Also, my north corner receives more reflected light becuase the wall is open to the sky and unencumbered by trees and tall shrubs; my mother's house, on the other hand, has a wide roof extension and trees planted along the wall, so the amount of reflected light is much reduced. Nothing much grows in Mother's shady north corner, even reflected light is blocked. It is almost like that absolute shade I remember near my ancestral home.

Defining shade that is anything less than full is more difficult. Most shade in nature is produced by trees and shrubs, yet even low-growing plants can provide shade. In wet meadows in central Japan, tall grasses shade the leaf mounds of wild species hostas, yet flowers on even taller scapes extend above the grasses, inviting pollination by insects. Any living plant, short or tall, will produce some shade, but trees are the natural shade givers. Here, in the morning, with the sun low in the sky, almost full sun reaches under the loblolly pines, brightening the garden. Later in the day the sun's rays are filtered through the long-needled, open tree branches and dapples the plants underneath with ever-changing patterns of light and shade. Further back in the garden, a Canadian hemlock casts a much denser shade; a little patch of English ivy is the only thing that grows beneath it, limbed up though it is. Along the eastern fenceline, a willow oak planted by a squirrel three decades ago allows almost full sun to reach under its leafless branches in midwinter, while in summer the large, multibranched tree crown casts cooling, dense shade. The hemlock's brances are horizontal, yet somewhat pendant, and close to the ground, giving shade that is much deeper underneath; the willow oak permints more sun exposure from the sides. Thus, three different trees — loblolly pine, hemlock, and willow oak — give various shade patterns throughout the year, changing with each season. Even the same tree species grown under different cultural situations can cast different intensities of shade. Most of my trees are pines, so Hosta Hill shade is dappled most of the time.

Photo: Hostas with ferns in the woodland.