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In rainy climates, additional watering may not be required. For climates that occasionally go without rain for several days to several weeks, additional watering is almost certainly needed. Check the condition of the soil on a regular basis. Once the surface feels dry, you should give the soil a thorough drenching. Never let the roots stay too dry for too long, even after the plant is established. Rather than giving small watering every day, give a heavy watering every few days. Feed the plant with a slow-release fertilizer at the start of spring, and give them an additional dose six to eight weeks later. You can either use an all-purpose fertilizer that contains equal parts nitrogen, phosphorus, and potassium, or you can opt for a fertilizer that contains higher levels of nitrogen and phosphorus. Phosphorus helps with root and flower development, while nitrogen aids in the establishment of full, vibrant foliage. Note that you should only apply fertilizer when the soil is wet. Water the soil upon application so that the fertilizer washes down below the surface. Fertilizer should also be applied during the early morning or evening, when the temperatures have cooled. Following both of these measures will prevent the fertilizer from burning your plant. Use bark chips or any other type of mulch that retains moisture well. Scattering a solid layer of mulch around the plant base helps the soil stay moist and also acts as a type of weed control. Additionally, decomposing mulch can add more nutrients to the surrounding soil. The plants spread quickly, and as they spread, large clumps of root form. The crowns of these clumps tend to rise above the soil. You should cover the crowns with loamy soil to keep the roots from drying out. The most common insects and diseases to attack the Astilbe plant include the tarnished plant bug, powdery mildew, and bacterial leaf spots. Even so, the plant is not especially prone to pests. If any of these problems do emerge, you can apply an appropriate insecticide or fungicide then. Preventative pesticides are not recommended, however. Every spring, you should take divisions of the Astilbe plant's roots to prevent the roots from choking each other out. You can replant these divisions to create new plants, give them to gardening friends, or discard them. You can use your divided plants to form a solid bed of color, or line a shaded garden pathway with your beautiful flowers.

Summary:
Keep the Astilbe regularly watered. Apply fertilizer at least twice per season. Keep a layer of mulch around the plants. Bury the crowns as they rise above the soil. Apply pesticide only as needed. Divide clumps every few years.