Stumbled upon this interesting piece from Ugly Duckling House. It's called How to Propagate Hydrangeas.
It gives us some fascinating ideas. This one, in particular, we thought was worth the share:
Some gardeners swear by rooting them in winter, where they’ll grow more resilient roots versus summer (which also makes sense). So, as of now, I have no recommendation as to what time of year is best. I’m simply taking what I cut off from pruning my hydrangeas in spring and summer and using those cutoffs for propagation.
Give the rest of this interesting article a read ...