Pennsylvania encompasses several U.S. Department of Agriculture plant hardiness zones, from 5a through 7b. Within this range, average annual extreme minimum temperatures range from 10 degrees Fahrenheit to minus 15 degrees. Selecting the best plants for partial shade in Pennsylvania involves choosing plants that suit specific Pennsylvania plant hardiness zones and soil conditions, which may range from predominately damp to quite dry.
Spring-blooming bulbs, like daffodils (Narcissus), generally hardy in USDA zones 3 through 9, perform well in Pennsylvania gardens shaded by deciduous trees. The flowers bloom before the trees leaf out and are unattractive to deer and other foragers that may frequent wooded gardens. For best results use early spring-flowering varieties and plant in the sunniest parts of the landscape. Varieties like "February Gold" and "February Silver" bear several flowers per stem and clumps increase over time. Interplant with perennial ground covers to hide the leaves, which should remain on the plants, nourishing the bulbs for the following year's blooms.
For spring color in partial shade, nothing beats old-fashioned bleeding heart (Lamprocapnos spectabilis, formerly Dicentra spectabilis), hardy in USDA zones 3 through 9, including all Pennsylvania zones. Lobed green leaves and arching stems of dangling pink "hearts" return every year and also self-seed. Spiderwort (Tradescantia virginiana) is another good choice for the Pennsylvania partial-shade garden. Spiderwort is hardy in USDA zones 4 through 9 and features long, strap-like leaves and abundant three-petaled flowers. Depending on variety, the flowers can be shades of blue, purple, pink or white. Shearing the plants after the flowers fade stimulates reblooming.
Among the best perennial ground covers for shade is bugleweed (Ajuga reptans), hardy throughout Pennsylvania and in USDA zones 3 through 10. Rosettes of scallop-shaped leaves hug the ground, giving rise to blue flower spikes in the spring. Ajuga spreads quickly to fill partially shaded areas and attracts pollinators. Big root geranium (Geranium macrorrhizum) also makes an excellent ground cover for partial shade, with lobed, apple-scented leaves that turn red in the fall. The pink spring flowers have five petals apiece and rise just above the leaves. These hardy geraniums perform well in USDA zones 4 through 8.
Anchor partly shaded perennial planting schemes with flowering shrubs that perform like perennials, adding height and multiple seasons of interest. Flowering raspberry (Rubus odoratus), hardy in USDA zones 3 through 8, features large, maple-like leaves and purple-pink flowers with five petals apiece. The sour fruits attract wildlife and the canes are thornless. Another fruiting plant that succeeds in partial shade is American cranberrybush (Viburnum opulus), which bears white flowerheads in spring, followed by edible red fruits. The leaves turn crimson in the fall. American cranberrybush is hardy in USDA zones 2 through 7.