Many gardeners plant shade trees as a shelter from our hot summer days, but once those trees mature, the problem becomes choosing plants to grow under them.  Shade plants are a whole different animal than those we plant out in the sun, and the challenge is to make the shady spots colorful and interesting while planting correctly to avoid straggly plants with disease problems.  First, you need to realize that shade is not created equal and is categorized as follows: 

Part Shade (semi-shade, half-shade) means that the location receives sunlight for at least part of the day, usually three to six hours, either in the morning or afternoon.

Light Shade (dappled shade, moving shade) defines a combination of sun, light and shadow.  This type has less light than part shade.

Full Shade means the area is nearly always in shade during the growing season; there is no direct sun at that time.

Dense Shade is the most difficult type to grow plants in.  It is typically found on the north side of buildings in urban settings where homes are built close together and can also be found under low-growing evergreens and under decks. 

Understanding the types of shade you are dealing with will help with selection of correct plant material.  When dealing with part shade, it is important to know whether the sun hits in the morning or afternoon.  There are many plants that like morning sun, but won't flourish when given full afternoon sun.  Eastern exposure is best for these plants which include shrubs like rhododendron, azalea, hosta, astilbe, bleeding heart and even ferns if given enough moisture.  In contrast, morning shade with afternoon sun is hard on shade-loving plants.  For this type of exposure, choose sun-loving plants or shade-tolerant plants that also do well in full sun; there are many listed as doing well in full sun to part shade that would fit the bill.

Light shade is ideal for most shade lovers; in fact, they thrive in this environment.  A garden can have as little as one to two hours of actual sunlight, but be bright most of the day.  Small, deciduous trees create dappled shade and larger trees that have been limbed up and/or had their branches thinned will provide light shade, but also bright light.  Reflective, white painted walls can create enough light for some plants even though the area is quite shady and in the absence of natural shade, a lath house or a canopy of shade-cloth mesh on a frame can provide the shade you need to grow your favorite plants.

Full shade is the ideal habitat for woodland plants which need protection from the heat of  summer, but need bright light during spring growth (when the sun is lower in the sky and shines beneath the canopy of high trees, or through trees that do not yet have their new leaves).  Again, additional light can be created by limbing trees to 20-30 feet, thinning excess branches and using reflected light from painted fences or walls.  If you are in the process of choosing your shade trees, select those with small rather than large leaves.

Dense shade is the least desirable for growing plants.  Ferns and some groundcovers will grow in this environment, but the best use of this space may be hardscape, such as paths and patios.  To provide some color, it is easy to rotate blooming plants in pots to this area and replace them when the shade causes blooms to decline.