To propagate hydrangeas by a process know as ground layering:
- Cut a notch in one of the branches of the main plant or scrape a little bark off the underside.
- Take the same branch, bend it over, and bury it in the ground. Make sure at least one leaf node will be underground.
- Use a brick to hold the branch down and retain moisture.
- When the branch forms its own roots, cut it loose and pot it like a cutting.