How to Propagate Hydrangea involucrata?
Propagate by softwood cuttings in early summer, or by hardwood cuttings in winter

Hydrangea involucrata · Hydrangea involucrata
Grow in moist but well-drained, humus rich soil, in sun or part-day shade. Mulch in spring, and provide shelter from cold, drying winds. See shrubby hydrangea cultivation for more detailed advice
Propagate by softwood cuttings in early summer, or by hardwood cuttings in winter