How to Prune entire-leaved astilbe?
Cut back stems and foliage before new growth begins in spring

entire-leaved astilbe · Astilbe simplicifolia
Grow in moist but well-drained or boggy soil in dappled shade, or in indirect sun where the soil remains moisture-retentive in summer. Drought intolerant, may be damaged in hot sun. Good for waterside planting. See Astilbe cultivation
Cut back stems and foliage before new growth begins in spring