Plumes of white, pink and red jet jaggedly upward from the fern-like foliage of astilbe (Astilbe spp.), often called false spirea. Growing from fleshy underground stems called rhizomes, these herbaceous perennials form dense clumps and range in height from 10 to 36 inches, slightly taller when the flower plumes appear. They do best in USDA Hardiness Zones 4 through 8 where a pronounced winter cold dormancy occurs annually.
Native to moist soils in woodlands, ravines and along stream banks, astilbe species hail from eastern Asia and North America. The only species native to North America bears the common name false goats beard (Astilbe biternata).
While taxonomic and horticultural authorities vary the number of species of astilbe to range between 12 and 24 species, most astilbe grown in modern gardens arose from numerous complex hybrid crosses. About six types dominate, each with cultivated varieties demonstrating desirable flower colors, foliage texture or mature growth heights. Arends astilbe (Astilbe x arendsii), were developed by the German plantsman George Arends. American perennial plant expert Dr. Allan Armitage notes that 95 percent of all astilbe sold in the United States derive from Arends' hybrid astilbes.
Other hybrids available for gardeners include those developed from Chinese astilbe (Astilbe chinensis), Japanese astilbe (Astilbe japonica), star astilbe (Astilbe simplicifolia), fall astilbe (Astilbe taquetii) and Astilbe thunbergii. The rose astilbe (Astilbe x rosea) resulted when the Chinese and Japanese astilbe were hybridized.
The foliage appears only during the frost-free growing season. Almost fern-like, each leaf comprises two or three segments of deeply cut leaflets with teethed edges. Some varieties produce coppery colored leaves, others varying tints of green. The flowers of astilbe are the prized seasonal ornamental feature. Occurring in late spring, summer or early fall--depending on species--tall plume-like or feathery clusters of tiny flowers range in colors from white, pink and red to purple, violet and shades thereof. The flower, or inflorescence, is called a panicle. The panicle arises from a central stem with many loose, open branches that line themselves with blossoms. After the flowers fade, they dry on the stem to shades of tan and brown, adding texture to the autumn and early winter landscape.
All types of astilbe grow well in a fertile, moist to wet, humus-rich soil or boggy location in a full sun exposure. If soils remain drier or in hotter summer climates, a shadier location helps prevent leaf edges from browning or flowering to be short-lived. Partial shade, broken shifting shade and sunlight across the afternoon works well in many gardens. Ideally the soils must never dry out in summer. Avoid planting in alkaline soils (pH over 7.5) or dry, heavy clay. Every three to four years the rhizome roots need division in early spring. Replanting the youngest, healthiest rhizomes ensures vigorous plants with excellent re-blooming for an additional three or four years in the garden.
Astilbe provides a burst of foliage texture and flower color for wet soils in woodland gardens or along stream banks. In swales where rainwater tends to naturally congregate and soils remain soggy, astilbe offers a low maintenance alternative to turf grass. Massive sweeps of differently colored astilbe flowers create dynamic landscape effect. Cut the flower stems for use in fresh flower arrangements, selecting the stems with only half of the tiny flowers open for longest vase life.