I am going to have to transplant my astilbes. The problem is, the area between the sidewalk and the astilbes gets sun. I would like a low-growing complimentary plant that will not hide the astilbes. Any suggestions would be appreciated.
So, to understand your question correctly: your astilbes are currently planted in an area that is too sunny for them, and so you are planning on transplanting them? Astilbes are members of the Saxifragaceae family and are hardy, herbaceous perennials.
True, astilbes have a fern-like foliage, (and are often companion-planted with ferns), and generally prefer shaded areas, but they can actually tolerate moderately sunny areas. The key here is to keep the roots moist, with a big, big drink once a week, and the soil that surrounds their roots should drain well. So please keep this in mind wherever you decide to re-locate your astilbes. And fertilize, compost and mulch all season long, to stave off possible ill-effects of any alkalinity in the soil. Astilbes bloom with plume-like flowers, and leaf in a beautiful, light, draping fashion, and need room to stretch — so plant them about 18″ to 2′ apart. As companions, either blue or gold varieties of hosta (Hosta sp.) would work well, as well as leafy, airy, ferns, or coral bells (Heuchera sp.). While these options are not necessarily “low-growing” they will work well to complement the foliage and leaf structure of your astilbes. This could be a wonderful gardening opportunity to try a variety of options that please your plants, and your sense of design.
Please also refer to this TMG link for more reading: Astilbes