Astilbe, also known as false spirea, is a flowering perennial and a member of the Saxifragaceae family, which includes mock orange, coral bells and piggy back plants. Astilbe can often be found planted in groups in perennial shade gardens and in woodland garden settings. Small or mature plants are usually purchased in containers from nurseries rather than started from seed.
Astilbe is a small -sized clumping perennial shrub that reaches about 1 1/2 to 5 feet tall and 1-2 feet wide. Some cultivars vary in size and may be slightly smaller or larger.
The compound green fern-like leaves are serrated at the edges. They may be a reddish-green color when new, fading to green as they mature. In some cultivars, the foliage stays that color permanently.
Astilbe is known for its feathery conical-shaped flowers that are 6-12 inches long. Flower colors range from white, pink, lavender, violet, purple and red. Flowers form on the very top of 1 1/2- to 5-foot-long stems in June through through September depending on the cultivar. The bloom period for an individual plant can last for 2-6 weeks.
Astilbe likes a very richly organic soil that is well-drained. They need to stay evenly moist at all times. They are best grown in full to partial shade but will not like full afternoon sun. They can be grown in USDA zones 4 through 9. In the warmer regions, hot summer days may trigger a dieback and dormancy. This can be avoided with regular irrigation. They benefit from an application of 5-10-5 fertilizer in the spring and summer.
Astilbe are best utilized in large group plantings. They can stay in flower all summer long if numerous varieties are planted together, because different cultivars have slightly different flowering times. They are also good for borders and entry ways. The fine leaves and flowers are used to contrast plants with larger broader leaves in perennial flower beds.
Astilbe chinensis is the species form that is native to China. Cultivars include 'Pumila' which is a dwarf variety reaching only 12 to 15 inches tall with purple flowers. 'Visions' retains its bronze-green foliage and has red flowers. The hybrid Astilbe x arendsii 'Fanal' reaches 2 feet tall and has dark red flowers. It has been a classic in gardens for over 60 years.