How to Water saw-toothed hydrangea?
Consistently moist root zone, add extra water during warm dry weather

saw-toothed hydrangea · Hydrangea serrata
Grow in moist but well-drained, humus rich soil, in a lightly shaded spot with shelter from cold, drying winds. Mulch annually in spring. Soil additives may be required to maintain specific flower colours. See shrubby hydrangea cultivation for more detailed advice
Consistently moist root zone, add extra water during warm dry weather