For that matter, what is full sun? That round, rayed, smiling face you used to draw at the top of your childhood sketches?
Actually, in horticultural terms, full sun generally means more than 6 hours of sunlight per day. Not every day, though, unless you live under virtually cloud-free desert conditions. So what “full sun” really refers to is a garden bed or windowsill which isn’t shaded by surrounding trees, buildings, etc. on the days the sun does choose to make an appearance. So the plants in that bed or on that windowsill can soak up the maximum amount of rays.
Most flowering and/or fruiting plants prefer as much light as possible, so full sun generally is a requirement for rose gardens, vegetable gardens, and orchards. It also is a necessity for most flowering houseplants, Mediterranean herbs, and flower borders--such as one of mine pictured in the banner image here which includes lilies, coneflowers, black-eyed Susans, etc. For plants which demand their “place in the sun,” south-facing flowerbeds or windowsills usually are the best option for those of us in the north, since Old Sol remains in the southern sky for so much of the year here.
Partial sun or partial shade generally means that the bed or windowsill receives at least 2 and no more than 6 hours of sunlight per day. Plants which will prosper in partial shade include perennials and biennials such as columbine, foxglove, and my primroses pictured above; annuals such as begonia, coleus, and fuchsia; herbs such as angelica, lovage, and mint; and houseplants such as clivia, cyclamen, and gardenia.
Partial shade flowerbeds or windowsills often are positioned on the east or west sides of buildings where they receive sun only in the morning or only in the afternoon. If the plant you want to grow prefers to “keep its cool,” as primrose does, an east-facing flowerbed is the best option, since the afternoon rays will be hotter.
Full shade generally means less than 2 hours of sunlight per day down to no sunlight at all. The question of which plants will thrive there generally depends on how bright that shade is. If the branches of the tree shading the bed are far from the ground, for example, the plants still should receive fairly bright illumination—perhaps even some dappled sun. Such conditions often are called “high shade,” “light shade,” or “bright, indirect light.”
Perennial plants which tolerate such conditions in my garden include those in the above image of a bed located on the north side of our garage. (Keep in mind that flowerbeds on the north side of buildings often are shaded by the building itself, even though there may be no trees nearby.) This one contains the bleeding heart, hosta, lily of the valley, sweet woodruff, trillium, and wild strawberry pictured as well as astilbe, ferns, garden phlox, lemon balm, and sweet cicely. Annuals which can thrive in bright shade include impatiens, mimulus, and torenia; houseplants include the whole family of gesneriads—African violet, gloxinia. etc.
Plants which will grow in heavy shade are unfortunately few and far between, though some ferns and mosses may be able to manage it. If the tree doing the shading is deciduous, though, you often can plant spring-flowering bulbs beneath it—since they should be finished blooming by the time the tree leafs out. Then you can sit in its refreshing shade during the hottest days of summer to contemplate the more sizzling sections of your garden.
Photos: The photos included in this article are my own.