Modern gardens are shadier now than they ever have been. Ranch houses that were popular through the middle of the last century had those classic big eaves that shaded wide margins close to the homes. Prior to that, tall Victorian houses made big shadows. Modern houses though are even bigger. To make matters worse, lots and garden spaces are smaller and surrounded by ominously tall fences; so there is less space that is not shaded by something sometime during the day.
This is why small trees, sometimes known as ‘micro-trees’, are so popular. They are all that fit into some small gardens without creating too much shade for other plants. Large shrubbery, like some of the larger types of pittosporum, and some of the smaller types of podocarpus, often function quite nicely as small scale trees. Where not too shaded, pineapple guava and New Zealand tea tree are just as effective. They only need to be allowed to develop upper canopies with adequate clearance, while their lower limbs get pruned away, instead of getting pruned to stay down low as shrubbery typically does.
Camellia, hydrangea, aucuba, Japanese aralia, Oregon grape and Heavenly bamboo (Nandina spp.) are appealing shrubby plants for shady locations. Camellias and hydrangeas of course provide impressive blooms during their respective bloom seasons. Camellias also have the advantage of excellently glossy dark green foliage all year; but hydrangeas are bare and need pruning in winter. Oregon grape and Heavenly bamboo, which are actually related, are more subdued but look more woodsy in bloom, and sometimes provide interesting berries afterward. Aucuba and Japanese aralia do not need showy flowers because their foliage is so bold. Japanese aralia has bigger and bolder leaves, but common types of aucuba are spotted with gold.
Balsam (Impatiens spp.), which is already one of the most popular warm season annuals that is beginning to get phased in as the weather gets warmer, is not quite as colorful in the shade as it is with better exposure, but can be impressive nonetheless. Cyclamen takes shade as well, but will actually be getting phased out through late spring and summer. Cyclamen is actually a perennial that can stay in the garden (if it is not in the way of anything else) to regenerate next autumn. As weather gets warmer in spring, caladiums and coleus can provide remarkably colorful foliage for shady spots through summer and early autumn.
Various types of ferns, although devoid of flower color, provide distinctive and often bold form and foliar texture. Australian tree ferns can actually get quite large and eventually function as small trees. Baby tears is a finely textured perennial ground cover that spreads as far as it has moisture. It can actually get to be invasive.