If you have a standout plant like a smoke bush (Cotinus coggygria), you'll want to do everything you can to help it shine, and that includes choosing the right companion plants. Smoke bush grows in U.S. Department of Agriculture hardiness zones 4 to 9 and prefers full sun, eight hours or more a day. It will grow in partial shade but won't become as full as in the sun. Companion plants should have the same growing requirements as the smoke bush. Stacie Palmer, landscape designer at Dennis’ 7 Dees Landscaping and Garden Centers, recommends planting smoke bushes with ornamental grasses, perennial flowers or with other smoke bushes.
1. Multiple Smoke Bushes
Plant several of the same cultivar together to form a smoky-looking hedge, or choose different cultivars with complementary colors. Smoke bushes' leaves can be yellow or purple, depending on the cultivar, and the wispy, pink or purple filaments left after the flowers have bloomed give the plant its smoky appearance. The leaves turn purple, red or orange-yellow in the fall. When allowed to grow to its full height, the smoke bush is actually a tree, but you can prune it to 15 feet by 15 feet or less and keep it as a bush. "Golden Spirit," with its bright yellow leaves, would look gorgeous next to a smoke bush with purple leaves, such as "Royal Purple," "Black Velvet" or "Velvet Cloak."
2. Ornamental Grasses
The size, color and texture of purple fountain grass make it a natural pairing with the smoke bush. Purple fountain grass (Pennisetum setaceum "Rubrum") is hardy in USDA zones 8 to 11 but can be grown as an annual in cooler climates. It needs full sun. This ornamental grass grows to be 2 to 4 feet tall and 2 to 3 feet wide. Its burgundy blades are topped with feathery rose-red plumes, somewhat reminiscent of the smoke bush's filaments. Some do consider purple fountain grass to be invasive. Pink muhly grass (Muhlenbergia capillaris), hardy in USDA zones 6 to 9 but used as an annual in cooler climates, is another possibility. This grass is 18 to 36 inches tall. In late summer, soft pink plume heads appear, also similar to the smoke bush's filaments.
3. Perennial Flowers
You can plant perennial flowers that bloom at different times so there will be a constant crop of companion plants for your smoke bush. Choose flowers the same color as the smoke bush for a monochromatic look, or choose colors on the opposite side of the color spectrum for a complementary look. In the early spring, yellow daffodils (Narcissus spp.) are a favorite. They are hardy in USDA zones 3b to 10 and grow 1 to 2 feet tall. Follow this with a late-blooming tulip, such as La Courtine Single Late Tulip (Tulipa "La Courtine"), hardy in USDA zones 3 to 8. Plant the Shasta daisy (Leucanthemum x superbum "Becky"), hardy in USDA zones 4 to 9, for flowers that bloom into September.
Groundcovers also pair well with smokebushes. Variegated lilyturf (Liriope muscari "Variegata") grows in tufts of yellow and green-striped blades and has purple flowers that bloom in the summer. Lilyturf grows to 12 inches tall. It is hardy in USDA zones 4 to 9. Pyramidal ajuga (Ajuga pyramidalis), hardy in USDA zones 5 to 9, forms a low, 3- to 4-inch tall mat of dark green leaves. In the spring, ajuga has violet blue flowers.