Sometimes called false spirea or feather flower, astilbe (Astilbe spp.) is among the best flowering perennials for moist, shady gardens. While about 25 species exist, many modern hybrids are grown in gardens nowadays thanks to the early 20th-century breeding efforts of Georg Arrends in Germany. Astilbes provide leaves of deep green to coppery, reddish-green and produce flowers in an array of colors from white to red.
Astilbe mix refers to any group of plants with a varied composition. Nurseries, especially mail-order, sell individual cultivars of astilbes in an attractive collection that highlights the diversity of flower colors. Moreover, plant breeders create collections or series of plants will similar characteristics, like leaf size or mature plant heights, but with different flower spike colors. For example, the Astary series contains multiple plants that produce either white, pale pink, rosy pink, magenta and salmon flowers. Nurseries may market this series as the Astary xix or a generic astilbe mix.
Astilbe plants hail from montane ravines, stream banks and woodlands across temperate eastern Asia and a few in North America. The vast majority of astilbes grown today are the result of complex hybridization among many wild species, according to the American Horticultural Society's "A-Z Encyclopedia of Garden Plants." Other than Arends creating many hybrids in Germany, nurseries known for release of new astilbe cultivars include Lemoine Nursery in France and Bressingham Gardens in England, as listed by perennial plant expert Allan Armitage of the University of Georgia.
Astilbes are widely known by gardeners to be plants for a woodland or shady nook of the garden. They relish humus-rich soils that are moist constantly. Although many authorities, like Ohio State University, recommend planting astilbe in partial-to-full shade, they do tolerate considerable sunlight if their roots are kept shaded and cool with lots of water. The cooler the summer temperatures, the better for astilbe plants.
A mix of astilbe in a landscape leads to a vividly colorful flower display in early or midsummer. Various plants create an attractive display of upright plumes of tiny flowers. Each flower plume measures anywhere from 7-to-18 inches long and dries to various shades of tan and brown by autumn. The more contrasting the flower colors in a mixed planting, the more visually striking. Depending on the cultivar, flowers range from clear white to ivory, to many shades of pink and red, to hints of violet or purple.
"A-Z Encyclopedia of Garden Plants" mentions that astilbes need supplemental irrigation in heavy clay or alkaline pH soils to look and perform their best. Dry soils and those lacking lots of organic matter require more maintenance. Dig up and divide the plants every three-to-four years, discarding the oldest woody rhizome roots. This replanting reinvigorates leaves and flowering. Stems of astilbe flowers are excellent cut flowers for bouquets, but they aren't long lasting -- perhaps no more than four-to-seven days if vase water remains fresh.