Also known as False Spirea, astilbe is a perennial that grows 18 inches to 5 feet tall. The large plumes of astilbe add a touch of color to a shade garden. Some varieties of astilbe, like Deutschland, bloom in early spring. The Ostrich Plume variety blooms in late spring while Pumila can bloom as late as July. Looming-over fern-like foliage, the faded astilbe plumes turn to a brown-rust color and will produce seed.
Plant astilbe in light shade according to the nursery’s instructions. The plant grows best in moist, humus soil. For areas lacking humus soil, add about 1 inch of topsoil or organic material and work it into the soil.
Apply fertilizer in early spring and again in the fall. Use a slow-release fertilizer for acid-loving plants like that designed for rhododendrons and azaleas, or you can use compost.
Apply 2 inches of mulch keeping the mulch 3 inches away from the crown of the plant. Keeping the mulch away from the crown (where the center stems meets roots, which is at ground level) helps to prevent formation of mildew, a potential problem of plants grown in moist areas and limited sunlight.
Remove foliage that has been affected by powdery mildew, which appears as a white coating. Powdery mildew may be prevented through careful watering at ground level so water does not hit the foliage.
Leave the foliage through the winter and then cut it down to the new growth in the spring. Cut the plumes if desired; however, if you leave them, the astilbe plant will self-seed.
Divide the plant every 3 to 4 years in the spring or fall. If dividing in the spring, dig up the plant just as new growth appears. Pull the clump apart, or cut or use a spade to force the clump apart. Follow the planting information from the initial plant if you still have it for how far apart to plant the clumps. Generally, plants that grow up to 2 feet tall should be planted at least 18 inches apart; 2 to 3 feet tall, 24 inches apart; over 3 feet, 36 inches apart.