How to Grow Astilbe

Light: Astible grows best in part shade. It can thrive in full sun, but will need shade in the afternoon in hot summer climates. In full shade, flowering will be reduced.

Soil: Astilbe thrives in moist, well-drained soil that has a slightly acidic pH (6.0). Add organic matter to keep the soil from drying out. If soils dry out the foliage may curl and scorch during the hot summer.

Spacing: Space astilbe plants 18 to 24 inches apart. The clumps will spread quickly when grown in the best conditions and will need dividing every 3 to 4 years to keep them in bounds.

Planting: Plant astilbe in spring or fall. Avoid summer planting due to astilbe's aversion to drying out. Astilbe can be started from seed, but it may be hard to germinate and will take a few years to get a substantial plant. Since astilbe spreads easily, a better way to get new transplants is to divide mature plants.

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.

Dividing & Transplanting needs: Astilbe will spread over time. If the desired result is a swath of plants along a pond, on the edge of a forest or in the garden, then dividing isn't necessary. However, if you want to keep it contained in a flower garden, divide it after the third year of growth or when the plant seems to be growing out of bounds. In spring or early fall, dig up the clump and divide it into 1 foot diameter sections. Replant in compost amended soil in a location with similar light and soil conditions as the mother plant. Keep well watered.

Pests/ Disease: The biggest problem for astilbe is the soil drying out causing the leaves and flowers to curl, brown and die. Planting in well-drained soil and keeping the soil moderately moist, but not soggy, is critical. Chinese species of astilbe have better drought tolerance than other species.

Woodchucks, rabbits and Japanese beetles may chew on the young foliage of astilbe. Two of the main pests of perennials, slugs and deer, seem to care little for astilbe.

To control Japanese beetles, apply beneficial nematodes or milky spore powder in the early summer and fall to kill the c-shaped, white grubs in the soil. These are the larvae of the adult beetles. Use beneficial nematodes in colder areas. To reduce the adult beetle population in summer, set out Japanese beetle traps at least 200 feet away from your garden in a perimeter around your property. In this way the flying beetles will find the traps before your plants. You can also handpick the adults in the morning while they are sluggish and drop them in a pail of soapy water.

Erect a low fence buried 1 foot into the soil to keep rabbits and woodchucks away. You can also spray repellents. Reapply them after a heavy rain and as the foliage grows through the season.

Although hardy to USA zone 4 when grown in the ground, astilbe aren't the best container perennials. But the flowers and leaves are excellent for cutting and using in arrangements indoors.