Q. How can I overwinter hydragea?
Mop-head and lacecap hydrangeas (H. macrophylla) need winter protection in areas where the temperatures fall below 5 or 10º F. These hydrangeas flower on old wood, i. e. from buds produced the previous summer, and they need to be protected from freezing. Paniculata, and smooth hydrangeas (H. arborescens) only need protection in the coldest locations of the US.
There are several precautions that can be taken to minimize winter damage to hydrangeas: (i) water well in the late fall, (ii) apply a layer of mulch around the plant once the ground is frozen, (iii) water the plants in the winter if the ground does not freeze and (iv) erect a physical barrier around the plant This is usually done by driving a number of wooden stakes into the ground around the plant and then stapling burlap around the stakes to form a cage, An alternative method is to erect a chicken wire cage around the plant and to fill this with dead leaves.
Hydrangeas in containers should be taken indoors to a cool, dry location where they can complete their dormancy during the winter, if possible. If left outside, then the container should also be wrapped, e. g. in bubble wrap, to prevent the roots from freezing.