If you don't want to wait years for a shade tree to grow or you are looking for something less permanent to provide shade, consider using flowering perennials. Although the shade won't be what a maple gives, tall perennials can offer some respite from the sun in the summer and transparency when light is most needed in the winter. In addition to creating shade, perennials that reach 5 or 6 feet can also act as as a privacy screen. Debbie van Bourgondien from van Bourgondien, a bulb nursery, goes even further by suggesting the creation of your own secret garden.
Choose a location where you need a shading effect and observe light levels during the day, preferably at a time as close to summer as possible. You may want to create an island area in the hottest part of your backyard or are thinking of using plants close to the house to help with cooling. Perhaps you want to expand a woodland area by planting tall shade perennials or create a shady area where shorter shade plants can grow. Keep the sun's direction in mind.
Decide how tall you want the plants to be at maturity. On average, it takes a perennial about three years to reach full growth. Garden writer Nancy Ondra recommends choosing plants that grow fast, such as Joe Pye weed (Eupatorium), especially the variety Carin, which can be 6 foot tall in midsummer. Although Ondra is primarily interested in privacy screening, her advice on tall plantings can be applied to the goal of creating shade. She discusses the qualities she looks for in plants: they must be able to stand upright without staking and have foliage density.
Do some research. There's a wealth of information available in perennial reference books, gardening magazines, mail-order catalogs and online. Nurseries such as van Bourgondien offer catalogs and plant information on their websites. Check heights, light preferences, bloom times, color, hardiness and the pros and cons of a variety of plants. No plant is maintenance-free, but you do want easy care. Jot down pertinent information and ideas in a notebook.
Narrow your choices. For example, you may love the look of hollyhocks, but discover they do best planted in front of a fence or a wall and may need staking. Not the best choice for an island planting, but perfect next to the house. They're also prone to the fungal disease rust which is unsightly but not fatal. Do you pass on hollyhocks or do you plant them and remove the affected leaves? By this method, you'll find the right plants for your situation.
Consider plants you may not have heard of or seen before. Ironweed (Vernonia) is a purple late-season bloomer recommended by Nancy Ondra. It has sturdy stems that rarely need staking. She also uses ornamental grasses, especially the upright bluish-green varieties of switchgrass (Panicum). Debbie van Bourgondien is fond of Giant Shirley foxglove (Digitalis) and lavatera, a hollyhock relative. The foxglove at 4 to 5 feet provides shade for plants in front of it and the lavatera grows quickly.
Extend a woodland area by using tall shade perennials. The University of Minnesota has compiled a list, admitting that tall plants are not numerous. However, there are a few, such as black snakeroot (Actaea) that will grow to 6 feet tall and has white bottlebrush flowers. Also good for shade are leopard plant (Ligularia), a yellow-spiked perennial, and Culver's root (Veronicastrum) with its white "candles," as described by the University of Minnesota Extension.
Debbie van Bourgondien suggests using the perennial vines such as clematis. A trellis or some sort of support is needed since the clematis is slow growing; she suggests planting annual vines to fill in while the clematis is growing.