Hydrangeas need protection from harsh winter temperatures, freeze, thaw, and drying winds. Depending on your climate zone, you may need more or less protection to winterize hydrangeas. Some gardening experts say that H. macrophylla—the common mophead or lacecap hydrangeas in shades of blue and pink—are the only hydrangeas that really need winter protection. Annabelle and Pee Gee (paniculata) do not require this treatment.
Here is a simple blueprint. If winter temperatures do not go below five to 10 degrees Fahrenheit, or only dip into single digits for an hour or so, hydrangeas should be okay without winterizing. But if winter protection is required, the steps are simple and straightforward. Here's what to do.
Step 1 - Assemble Materials
Gather all materials for winterizing when hydrangeas go into dormancy, which is after all the leaves have fallen off.
Step 2 - Lay Out Stakes and Surround with Chicken Wire
For the cage winterization method for hydrangeas, lay out the stakes and pound them into the ground around the plants. Stretch chicken wire around the outside of the stakes. Cut the material to fit and attach with garden clips, wire, or plastic ties.
You can also insulate by wrapping burlap around the stakes.
Step 3 - Tie Back Hydrangeas
Since the object of winterizing mophead and lacecap hydrangeas - which set blooms on old growth wood - is to protect the buds from temperature extremes, tie the branches loosely together inside the chicken wire cage or burlap enclosure.
Step 4 - Surround with Mulch
Next, add the insulating material inside the enclosure, working down to the base of the hydrangeas. Be careful not to damage the tips of the branches, which is where the buds will bloom come spring.
For additional protection, you can add insulation cloth inside the entire cage.
Step 5 - Cover with Styrofoam
This step may not be necessary, but in areas where there is heavy snowfall, it is probably a good precaution. Once the cage has been constructed and insulating material added, cut a one-inch thick piece of styrofoam the diameter of the cage. Place it inside the top of the cage, gently compressing the leaves in the process.
Other Winterizing Methods
For potted hydrangeas, simply cover them with sufficient protective material and keep them out of harsh winter winds. You can lay the pots on their sides on a waterproof tarp and fill with insulating material. Another method involves placing styrofoam cones over the top of the plants.
Alternatively, tape large pieces of one-inch thick foam padding into place around and over the top of the potted hydrangeas. Of course, you can also bring smaller potted hydrangeas inside to a basement or garage that only freezes lightly.