The astilbe, a perennial flower also known as false spirea, grows best in a partial to full shade gardens in USDA Hardiness zones 4 through 8. The plant varies in height from 1 to 6 feet and produces flower plumes in red, white or pink. The astilbe grows best when given proper care through fertilizer, organic matter and water applications to maintain a healthy plant.
Work 2 to 3 inches of organic compost into the garden soil at the time of planting to add a natural fertilizer and increase the soil nutrient value.
Apply a 2 to 3 inch layer of organic mulch over the soil area around the astilbe plants. Refresh the mulch each year to maintain an adequate layer. The mulch will break down and seep into the soil to provide a natural fertilizer to the astilbe plants.
Apply a 5-10-5 flower fertilizer each month during the summer to stimulate flower growth. Follow the package instructions for fertilizer application rates based on the square feet of garden space.
Apply a high-nitrogen flower fertilizer each fall after removing all spent flower blooms from the astilbe.