The Right Place
Astilbes like partial shade, especially in the warmer southern climates. In the north they can handle full sun. If you have a damp spot somewhere these just might be the plants to grow there. They like moist soil rich in organic matter that may be slightly acidic. The soil can even be wet during the season, but it should not dry out in winter.
Planting Nursery Stock
Astilbes come as either bare root crowns or in containers. Plant the crowns in the early spring. Potted plants can be planted any time up through mid-August. Clear the planting area of weeds and debris and loosen the soil down 6 or 8 inches with a trowel or shovel. Remove any large stones or other obstacles and level the area.
Dig a hole that is slightly larger than the rootball of your astilbe and just as deep as the container or the soil mark on its bare stems from when it was previously planted in soil. Set the plant in the bare hole, taking care that it is firmly set so that it is at the level in the soil that it was previously. Since they have shallow roots, it is very important not to plant astilbes too deeply. Be sure the "eyes", the potential new shoots, are only 1/2 inch below the soil surface. Fill any remaining space in the hole with soil, pressing it gently around and over the roots to remove air pockets. Water well and often over a few weeks until the plant is well established. Do not fertilize at this time. Space plants about 12 to 18 inches apart.
Astilbes grow wider quickly through their spreading roots. To control their size and acquire more plants, divide the clumps every 3 to 5 years. Dig up each plant or clump and cut through the roots with a knife or sharp spade to sever chunks of new young rooted shoots from the older plants. Replant the smaller astilbes plants at the correct spacing in the same place and in other areas around the yard.