Photo credit: Kim Frey
One of the mistakes made by a beginning gardener is to put a sun plant where it receives too much shade or a shade plant where it gets too much sun. It’s easy to do; we’ve all done it. Even if you read the plant tag for the plant’s light requirements, you can make an error. Often the problem is in defining what constitutes full sun, full shade, and partial sun or shade. Many gardeners aren’t certain; it can be confusing. The light available to a plant, however, will directly impact its success. Different plants need different amounts of sunlight to produce enough food to grow and maintain health and vigor. Before you select plants, therefore, it is important to understand light conditions in the garden.
Defining Sun and Shade Conditions
Most sources agree on the following definitions:
- Full sun is six or more hours of direct sunlight per day. This doesn’t need to be continuous, for example there could be four hours in the morning, shade midday, and three or four hours of sun in the afternoon. It must be direct, full sun.
- Partial sun is between four and six hours of sun a day.
- Partial shade is two to four hours of sun per day.
- Shade, in gardening terms, means less than two hours of sunlight a day.
You may come across the terms light shade, moderate shade, and heavy shade. They may be characterized as follows:
- Light shade sites receive partially filtered sun, such as that found under open canopied trees like honeylocust and birch, where there is an ever-moving pattern of sun and shade. You may see light shade referred to as dappled shade or intermittent shade.
- Moderate shade occurs with mostly reflected light, such as at the floor of a hardwood forest.
- Heavy or dense shade is a site with no direct sunlight, such as at the base of a north-facing wall or below dense evergreen trees. It is important to note that all plants need some light to survive.
Assessing Your Garden for Light
Before buying plants, it is a good idea to actually measure the amount of sun your garden receives. You can purchase an instrument that measures light, but your own observations are just as useful. Dedicate a day to do this activity. Draw a simple diagram of your garden then go outside every hour, starting at 7:00 a.m., and mark which sections have sun or shade. Total the number of hours that each area has sun to determine which condition applies. Bear in mind, the angle of the sun affects the results, so that northern exposures become shadier in winter and southern exposures have more sun in summer. You may wish, therefore, to assess your garden for light with each season. Also, landscapes change their degrees of sun and shade over time: a sunny garden becomes shadier as trees and shrubs mature and the removal of a tree may cause a shady area to become suddenly sunny. Therefore, analyze the degree of shade in your garden periodically to determine if you need to move or change plants.
When selecting plants for any location, also consider all other requirements for their success: soil type and pH, hardiness zone, moisture needs, and possible pests and diseases. Contact your county Extension office with specific questions.
Gardening in Sunny Areas
Sun loving plants in general have thicker but smaller leaves that tolerate more light than shade plants. Most vegetables, and some of the best flowers for cutting, need six or more hours of direct sun each day and would be happy with more.
Plants for Sunny Areas
For the sunny garden choose black-eyed Susan (Rudbeckia hirta ‘Indian Summer’), yarrow (Achillea millefolium ‘Summer Pastels’), Shasta daisy (Leucanthemum x superbum ‘Giant Marconi’), bachelor’s button (Centaurea macrocephala and C. delbata ‘Aloha Rose’), calendula (Calendula officinalis ‘Indian Prince’), celosia (Celosia ‘Cramer’s Amazon’), cosmos (Cosmos Versailles Series), dahlia (Dahlia Karma® Series), snapdragon (Antirrhinum majus Rocket Mix), and zinnia (Zinnia elegans Benary’s Giant Mix.)
Gardening in the Shade
Many gardens have limited light levels due to an abundance of trees. The best way to cope is to choose plants that do well in less light. Shade plants often have thin leaves with large surface areas. Thus they are anatomically adapted to be efficient at photosynthesis in low light. Bear in mind that shade plants are most likely to tolerate some sun in the early morning. Being more sensitive to light reduces their ability to withstand direct sunlight for an extended period of time: their foliage becomes bleached, their leaf margins scorch, or burn spots appear on the leaves. If you notice these signs you may relocate the plant or create additional shade by adding a structure or planting a shrub or tree nearby. Many shade plants have adapted to competition from trees, however, they may require supplemental water. To avoid the development of a fungus, always water plants in the morning to allow moisture to evaporate quickly from the foliage. Also, select disease resistant plants. Choosing shade lovers that are dry-site tolerant is the best option.
In spite of the challenges, shade gardens can be very rewarding. They are often more restful than sunny landscapes. They change through the seasons with beautiful spring blooms, interesting summer textures, colorful fall foliage, and winter evergreens. A woodland garden can be especially beautiful with its layers of trees, shrubs, and shorter plants. Add meandering paths to increase the enjoyment.
Plants for the Shade Garden
Penn State Extension provides a list of shade tolerant trees, shrubs, and groundcovers. Trees they recommend include: Allegheny serviceberry (A. laevis), kousa dogwood (Cornus kousa), American holly (Ilex opaca), and staghorn sumac (Rhus typhina.) Some of the shrubs that tolerate shade better than most are chokeberry (Aronia arbutifolia), common sweetshrub (Calycanthus floridus), summersweet (Clethra alnifolia), dwarf fothergilla (Fothergilla gardenia), and witchhazel (Hamamelis spp.). My favorite groundcovers on the list are wild ginger (Asarum canadense), astilbe (Astilbe spp.), plumbago (Ceratostigma plumbaginoides), sweet woodruff (Galium odoratum), Lenten rose (Helleborus orientalis), coral bells (Heuchera spp.), crested iris (Iris cristata), stonecrop (Sedum spp.), and foamflower (Tiarella cordifolia.)