Dark shade is typically defined as being very dense and dark, such as the area under evergreens. The choice of plants tolerant of this type of shade is very limited due to the lack of sunlight as well as the soil conditions. Soil around evergreens is acid in nature. You may improve the soil by adding organic matter, however, be careful not to damage the roots of the evergreens.

Medium Shade:

For the most part, deciduous trees provide medium shade. However, large trees may provide dense shade not suitable for many plants. Trimming of tree branches may be necessary to allow ample sunlight to lighten the shade. Some trees may have roots close to the soil surface that consume a majority of the moisture and nutrients, which will make it difficult for new plants to compete. Spring-blooming bulbs planted under and around trees will receive plenty of sunlight before the tree's leaves are out.

Light Shade:

Light shade is the shade produced from a building or tree as the day progresses. The north side of a building or tree is considered bright, indirect light. Plants recommended for full or part shade will do well here. The East Side of a building or tree receives morning sun and bright, indirect afternoon light. Plants that prefer full sun and part shade will do well here. The West Side of a building or tree receives indirect morning light and full sun in the afternoon. Plants that prefer full sun and part shade will do well here too. The south receives full sun nearly all day long.

Shade Tolerant Perennials:

Ajuga varieties
Astilbe varieties
Convallaria majalis (Lily of the Valley)
Campanula carpatica
Dicentra spectabilis (Bleeding Hearts)
Digitalis (Foxglove)
Ferns
Galium odoratum (Sweet Woodruff)
Helleborus orientalis (Hellebore)
Hosta
Ligularia dentata
Myosotis (forget-me-nots)
Pulmonaria