Plant your astilbe in a full to partial shady location. The hole should be dug slightly larger than the rootball in an area protected by temperature extremes. Spread the roots out evenly and work the soil in between them as you firm the planting area. Water the plant to settle the soil and add additional media if necessary.
Mulch creates a barrier that reduces the chances of soil-borne disease and fungus from coming in contact with the plants, holds moisture in the soil, keeps the roots cool and helps control weed growth. For maximum benefit, mulch the soil around the plant to about a 2 inch depth, keeping it a few inches away from the plants stem.
Water the plants consistently and remember that newly set plants require more water with greater consistency than established plants which have mature root systems and built-up reserves. Water the new plants daily for a week or so and then slowly reduce the watering as the plant becomes established. Do not let the soil stay too wet, root systems need oxygen as much as moisture so make sure to check for moisture levels by digging down into the soil before you water.
For long-lasting plants, fertilize in early spring each year with a good natural fertilizer. Properly maintained soil will not need heavy applications of fertilizer. It is suggested that you allow the plants a chance to establish themselves first and then add fertilizer if needed. Weak, floppy stems can result from over-fertilization. If you are unsure about the soil in your garden, perform a soil test or contact your local Cooperative Extension Agency.