Astilbe (Astilbe chinensis), also known as false spirea, is an herbaceous perennial plant prized for its large flower clusters and ease of growth. The plant blooms during early to mid-summer, usually between June and July. It produces multiple plumes of flowers in shades of white, pink, purple or red, depending on the variety. Native to Asia and North America, astilbe requires only basic care to thrive in the home garden, and it makes an ideal planting for flower beds and borders around ponds or streams. Hardy in USDA zones 4 through 8, astilbe plants perform well in most areas of the United States.
Plant astilbe during mid-spring in a location that receives bright morning sun and partial afternoon shade when temperatures peak. Choose a site with well-drained, highly fertile soil for optimal growth. Space astilbe plants 12 to 24 inches apart.
Water astilbe once every five days during the first active season of growth to help establish the planting. Decrease the frequency of watering thereafter to once every seven days to keep the soil consistently moist. Do not water during winter, when active growth has ceased.
Feed the plant twice per year, once during early spring and again in mid-summer, using a 5-10-5 NPK granular fertilizer. Water the soil lightly before and after applying to dissolve the granules. Apply at the rate described by the instructions on the package.
Apply a 3-inch layer of mulch to the soil surrounding astilbe plants during early winter, just after the first frost of the season, to provide insulation for the roots. Begin the layer at least 3 inches from the plant's base to allow air to flow freely. Remove the mulch during early spring, just before new growth resumes.
Use pruning shears to cut back astilbe to the ground if the foliage begins to turn brown and die during summer. The plant will rejuvenate if cool, moist conditions return, or will stay dormant until the following spring if it is unable to recover.