One of the most important elements in the garden environment is shade. Unlike some of the other components, shade occurs to some extent in every garden. It dramatically alters the air and soil temperature, especially in arid regions, and it often raises the humidity.
When selecting plants for a shady area, keep these points in mind: Most sun-loving plants will accept some amount of shade during part of the day as long as they also receive the amount of direct sun they need. Shade-loving plants, on the other hand, will wilt, sunburn, or develop other signs of distress from too much direct sun (especially the hot late-afternoon sun) even if they receive adequate shade for the rest of the day.
When a plant is placed in shade too deep for its needs, it produces long, weak stems and fewer leaves than normal. The plant stretches toward the light it needs, a phenomenon called etiolation. The process of etiolation weakens the plant. It may appear healthy for a while, but it is using stored energy. If left in this declining state for too long, the plant may not regain its vigor even if it is transplanted to a sunny spot in the garden.
Shade produced by open trees—such as birch, which create a moving pattern of sunlight and shade across the ground—is called dappled. Shade cloth and lath houses also provide dappled shade. This is the lightest shade category. Most shade-loving and even many sun-loving plants grow well in dappled shade.
Shade cast by a north-facing wall, fence, or building is open shade. The distance the shade is cast varies with the season. Open shade provides bright light but no direct sunlight. Fiberglass-roofed patios and whitewashed greenhouses under direct sun also provide open shade.
Shade occurring in north facing locations further darkened by a structure or by trees—in other words, open shade in which light is further obscured—is called medium shade. This situation also occurs under decks and stairwells.
The deepest shade is dense shade. It is found in north-facing side yards in which tall walls or fences block all but the narrowest strips of light. There is some reflected light. Plant selection is severely limited in these areas.