Growth Habit: Astilbe is a clump-forming perennial with fern-like leaves and tall flower stalks with plume-like flowers. Plants range in size from 1 to 4 feet tall. Astilbe looks best planted in groups and some low growing types make excellent ground covers. The brightly colored flowers last for a few weeks. Some gardeners will deadhead the flowers after this to keep the bed looking neat. But the flowers and seed heads maintain some of their color, even after drying on the plant, and can be attractive for a few months.
Staking: Because of their strong stems, astilbe usually don't need staking. If tall varieties do flop in your garden, plants them closer together and in groups to support each other.
Watering: Astilbe needs to be watered deeply every week, especially during periods of dry, summer weather. If allowed to dry out, the foliage will brown and the plant may even die. However, astilbe doesn't like soggy soils, so over watering should be avoided.
Fertilizing: Amend the soil at planting with compost. Each spring add a 1- to 2-inch thick layer of compost and a balanced organic fertilizer, such as 5-5-5, to help stimulate new growth and flowering. Side dress with another dose of organic fertilizer in early summer.
Trimming & Pruning: Although astilbe can be deadheaded after the flowers fade for a neater appearance, it isn't essential. As with any herbaceous perennial, cut astilbe plants to the ground in fall to clean up the bed. This will reduce the number of diseases and overwintering insects.
If plants dry out and the foliage curls and browns during the summer, cut back the plant to the ground, water well and hopefully it will regrow to be attractive for the rest of the season.
Mulching: Astilbe benefits greatly from an organic bark mulch added each spring. Since astilbe does't like to dry out, the mulch helps maintain soil moisture and adds organic matter over time to the soil. Mulch also prevents weed growth, allowing the plants to fill in quicker.