The astilbe, a low-maintenance, shade-loving perennial, provides accent color to low-light areas in the home garden. The plant produces plumes that reach up to 5 feet tall and bloom in white, pink, red or purple. Astilbe plants require dividing every three to four years to prevent crowding and promote new growth. Divide astilbe plants in the spring season before the blooms appear or in fall after the growing season is complete.
Prepare a new planting location for the astilbe plant. Choose a location that has partial to full shade and well-draining soil. Test the soil pH. Astilbe grows best in an acidic soil with a pH of approximately 6.0.
Amend the new planting location two weeks prior to planting. Work ground rock sulfur into the soil to lower the pH if necessary. Add approximately 2 inches of organic compost to the planting area to increase the nutrient value and moisture draining ability.
Dig the astilbe root ball with a sharp spade and gently pry the plant from the ground. Remove as much of the root ball as possible. Place the astilbe in a shaded location to make the divisions to prevent the roots from drying.
Gently separate root clumps that form off the main root crown. Each division should include a healthy section of root and foliage for best results. Discard the root crown if there is no green stem growing from it.
Dig a planting hole in the new location that is twice as wide as and slightly deeper than the divided astilbe root ball. Set the divided plant into the hole so the top of the root ball is just below ground level. Place two divided sections in the hole if the plants are small.
Fill the hole with soil and gently pack to hold the plant in place. Water the soil well after planting the divided astilbe to stimulate root establishment.
Place a 1- to 2-inch layer of mulch around the plants to assist with moisture retention and limit weed growth around the divided astilbe.
Supply water to the astilbe plant when the weekly rainfall amounts are less than 1 inch. Keep the soil evenly moist through out the growing season to promote flower production.