The information presented here was largely taken from Dr. Beattie's paper catalog...
Astilbe History and Naming: George Arends, a noted botanist and nurseryman from Ronsdorf, Germany, is responsible for introducing the majority of the Astilbe cultivars, many of which bear his name. Most of the species and varieties Arends bred were from Asia - China, Korea and Japan. Interestingly, Arends seemed to have passed over the only American representative, A. biternata.
Due to the fact that the development of these colorful woodland wonders involved so many parents, the distinction among them is largely lost. Rather than try to name them as hybrids or to distinguish their parentage, they are assigned to groups. In fact, many of them are so similar that keeping them separated can be difficult, which is one of the reasons for so much name confusion. How many distinct, named taxa are there? Probably between 150 and 200. Many named varieties have been lost in cultivation, or were transported to nurseries and botanical gardens in Eastern Europe during the 20s, where they became effectively, "lost". With the lowering of the Iron Curtain and renewed contact with these organizations, new ones are being "found" each year. Over the years Dr. Beattie had found that there are many misnamed Astilbe. For instance, there are two 'Dunkellachs' on the market, and even Arends himself introduced a second 'Deutschland'. Most incorrect names have originated from inattention to detail. Bare-root Astilbe and even Astilbe not in flower are difficult to identify; therefore, great care must be taken at shipping time to maintain correct labeling.
Astilbe Culture: Astilbe are lime-haters and water-lovers. In nature, they grow along stream banks in partial shade, in soils whose pH is below 6 and where ample water is available, especially during the heat of summer. Although you can grow great Astilbe in hot areas, supplemental irrigation during the summer is a must, especially for the shallow rooted like 'William Buchanan'. Astilbe are also heavy feeders, so a light spring and fall application of an acid reacting, relatively high nitrogen fertilizer is helpful.
Astilbe are mostly clump formers and benefit from being divided every 4 years or so. YAG divides the Astilbe either in the early spring before leaves emerge, or after they are finished blooming in summer. Transplanting after September 1 is risky in our northern latitudes unless plants are mulched for winter. Some recommendations for landscape use for over wintering include cutting evergreen boughs and place them over new transplants beginning about December 1. These will help to collect snow, which is the best insulation available. Further providing shade in March reduces the chances of plants heaving out of the ground.
Landscape Use: Astilbe are effective in a variety of situations, either as specimen plants, or en masse; shorter types should be used at the front of the border and the soaring specimens at the back. Enjoy the presence of giants like 'King Albert', the graceful plumes of 'Straussenfeder', the "pat-em-on-the-head" tufties like 'Siska', or the diminutive demeanor of A. yakusimanum. However, Astilbe are at their best when showing off the bold textures of plants like Hosta, Bergenia, Pulmonaira, Ligularia, or Heuchera in shade gardens. Depending on the size of the particular variety, Astilbe should be planted anywere from 6" to 18" on center. Chinensis types, especially A. chinensis 'Pumila' are somewhat rhizomatous, and fill in nicely.
Spent plumes can be left on plants or collected for drying and use during other seasons for crafts or other purposes. Drying the plumes on the plant shouldn't be a landscape problem as Astilbe rarely seed in. Additionally, when left on the plant the bold presence of the plumes on the Gloria's, especially 'White Gloria', in the fall and winter garden are especially beautiful.
Pests: Although Astilbe are not bothered by many insects, they are high on the gourmet list for Black Vine Weevils. You'll know when these little bandits are present by the neat paper punch like notches on the leaf edges. Check with your local extension agent for insect control measures. Or consider more frequent divisions and relocation as an alternative pest prevention measure.