The types of plants that flower in shade diminish in number as the shade deepens. This is a harsh truth perhaps, but one that shouldn't discourage you from a shade garden. It can be interesting to try new plants, such as the Lenten rose (Helleborus). According to Judy Springer writing for the Brooklyn Botanic Garden, a half day of sun or "light shade" will get the best show from shade plants.
Flowering Perennials for Shade
Fernleaf bleeding heart (Dicentra formosa), foxglove (Digitalis), astilbe and even sun-loving daylilies will do well in light shade. With less light exposure, these plants will survive but won't flower as much or as long. For a woodland choice in part shade, try the marsh marigold (Caltha). The Missouri Botanic Garden lists several perennials that will grow in full to dense shade, such as Lenten rose (Helleborus orientalis) and bishop's hat (Epimedium). Both are early bloomers. so they may catch more light if your shade is deciduous, such as from maples or oaks. White wood aster(Aster divaricatus) blooms in full shade in late summer.
Flowering Shrubs for Shade
Rhodendrons, azaleas and hydrangeas flourish in light shade. In areas with less light, try mountain laurel with its large showy flowers in pinks. Sandra Mason, writing for the University of Illinois Extension, recommends trying the sweet pepper bush (Clethra) for its white fragrant flower spikes. The Missouri Botanic Garden recommends the yellow-flowered Japanese rose (Kerria) for dense shade.
Annuals for Shade
Annuals, such as impatiens, wax begonias and lobelia, do well in light shade and will be covered in flowers. They will survive in lower light levels, but flowering will be less. The Missouri Botanic Garden recommends the red Begonia 'Dragon Wing Red' for full shade. Annuals require frequent fertilizing during the season, and water is also crucial. A good well-drained, loose soil is beneficial as well..
Vines and Foliage Plants
The white-flowered climbing hydrangea and several types of honeysuckle vines will do well in light shade. The sweet autumn clematis(Clematis paniculata) also will be massed in white flowers in light to partial shade. Non-flowering vines such as ivies will do well in lower light levels. If light levels are too low for flowering plants, consider the foliage color from hostas. There are gold varieties available, as well as deep blue.