Astilbe are woodland flowers and do best in the shade of forest trees. Their airy foliage and plumes of flowers come in reds, pinks, whites, salmon and coral. Astilbe are hardy perennials in USDA hardiness zones 4 to 8 and flower from late spring to early summer. Selecting companion plants for astilbe includes considering hardiness, soil preference and sunlight requirements. Like many woodland flowers, astilbe grow quickly in the spring before the forest canopy blocks the sun.
A good background plant for the woodland garden, beauty bush grows up to 9 feet tall. Hardy in USDA zones 4 to 8, it will fade into the background after putting on a spectacular show of pink flowers in early spring. Most have green foliage, but some have bronze or yellow foliage that changes to golden orange in the fall, providing for season-long interest. Beauty bush should be pruned right after flowering is finished in late spring so new growth adds buds for the following spring. As an added bonus, beauty bush is deer resistant.
Considered an essential part of any woodland or shade planting, columbine is hardy in USDA zones 3 to 9. Growing up to 36 inches tall, columbine starts its flowery show about the time astible is getting ready to finish. With delicate, intricate flowers held above the green foliage on slender stalks, columbine is just right for planting around and behind the shorter astilbe. The flowers are usually two-toned with white petals and colored sepals (lower, outer petals) and come in reds, blues, yellows and pinks or pure white.
Grown more for colored foliage than flowers, coral bells is another plant well suited to the woodland or shade garden. Hardy in USDA zones 3 to 9, coral bells form little mounds and are great for edging shaded paths or the front of a shady bed. They flower mid-summer through early autumn, depending on variety, with the bell-shaped flowers hanging far above the foliage on sturdy stalks. Coral bells are deer resistant, the foliage ranges from green to gold to deep red.
Bugleweed is a short, 3- to 6-inch tall perennial hardy in USDA zones 3 to 8. Late spring brings a forest of blue or purple flower stems above the dark green or dark purple foliage. Bugleweed makes an excellent ground cover, and spreads through rhizomes. The plant is vigorous and usually evergreen, providing interest year-round. Bugleweed is deer resistant and requires good shade. It does poorly in very hot and humid climates.
A native woodland plant, trillium is hardy in USDA zones 3 to 9. The plants form densely populated groups on the forest floor, with each plant bearing three leaves. The flowers of white, red or pink show themselves from early spring to early summer. Trillium is deer resistant and makes a good ground cover, once established. Trillium will do just fine by themselves and prefer to be left alone. The best success is with transplants, as trillium seeds are notoriously difficult to start and take up to three years to germinate under ideal conditions.