How to Care for Astilbe

Finding color for a shady garden isn't always easy. Astilbe (Astilbe spp.), a shade-loving perennial that grows in U.S. Department of Agriculture plant hardiness zones 3 through 9, depending on variety and species, fills the need for color and texture in these sometimes troublesome areas. Its feathery and vibrantly colored flowers rise above serrated foliage to create a texture-rich focal point even in heavy shade.

Both Chinese astilbe (Astilbe chinensis, USDA zones 4 through 8) and hybrid astilbes (Astilbe x arendsii, USDA zones 4 through 9), do best in partly shady or areas with full shade but can handle full sun if the soil is kept moist. The soil should be rich, fertile and well-draining, but don't allow it to dry out at any point.

Water an astilbe thoroughly and deeply during periods of drought to keep it healthy and vigorous. Chinese astilbes tolerate dry soil slightly better than hybrids.

Astilbe does best with additional fertilizer and responds well to a high-nitrogen fertilizer in fall. Use an organic fertilizer, such as bat guano, in fall. Apply the bat guano at a rate of 1/4 to 1/2 pound for each 25 square feet of flower bed. Wear a dust mask when spreading the guano. Mix the guano into the soil thoroughly and water the area deeply.

Mulch and compost in spring help keep your astilbe bed fertile. Apply a thin layer -- 1 to 2 inches -- of organic compost, either homemade or store-bought, every spring and top your astilbe bed with a 2-inch layer of mulch. The compost breaks down into the soil, adding nutrients, while the mulch helps reduce evaporation to keep the soil moist.

Astilbe forms new clumps throughout its life. Divide the plants every three to four years in spring. Division encourages healthy plants while also allowing you to create new astilbe beds. Dividing requires digging up the plants and separating the rhizomes with your fingers to form smaller clumps. You have the choice to discard excess astilbe plants or plant them in other parts of your yard.

Dig a trench around the drip line -- how far the leaves extend out on your astilbe. Slice through the roots cleanly with the shovel and work inward toward and under the plant to dig out the root ball. Gently divide the thick roots to form new clumps.

Astilbe doesn't need regular pruning, but deadheading can help neaten the plant and prevent too many new plants from growing if self-seeding is a problem. If you like the way the seed-heads look, you can leave them on the plant or prune them off to tidy the plant.

Pinch dead leaves with your fingers throughout the growing season and cut your astilbe to the ground in early spring to encourage growth. If you decide to cut your astilbe back, disinfect pruning tools by dipping them in a solution of equal parts water and antibacterial household cleaner, then allowing them to air dry.

Astilbe is a tough plant, although it is susceptible to a handful of pests and diseases, none of which cause considerable damage to healthy plants. Pests include Japanese beetles, plant bugs and whiteflies, but they rarely cause enough damage to worry about. Handpick beetles and true bugs. Use a strong stream of water from your garden hose to knock off whiteflies and aphids.

Diseases include cercospora leaf spot, along with powdery mildew. Neither is likely to kill the plant. In the case of fungal powdery mildew and cercospora leaf spot, thin your astilbe plantings to encourage better air circulation. To thin them, prune out select stems and leaves in the astilbe to reduce stem crowding and help allow more air to move through the plant. Also avoid overhead getting astilbe leaves wet when you water -- water with a soaker hose or at the base of the plant. Cut off and destroy infected plant parts -- using sterilized tools -- to reduce the spread of problems you see.