Answer: Snow cover is actually an excellent insulator and not to be feared. Apply a layer of organic mulch about three inches thick over the root area in late fall after a frost or two. Do not allow it to touch the stems, keep it an inch or two away. All of the shrubs, and the perennials, will benefit from mulch.
If you have a Hydrangea arborescens or Hydrangea paniculata shrub, mulch alone would be sufficient protection. These both bloom on new growth of the season so there is no need to worry about protecting the flower buds. The arborescens type is usually cut to the ground in spring, the paniculata needs little pruning unless you want to shape it in some way. If so, do that in late winter or early spring.
If you have Hydrangea macrophylla (big leaf hydrangea), pruning is minimal. Wait until late spring and prune off any winter killed branch tips if necessary. A new hydrangea will not need much if any pruning for the first few years apart from that. Eventually you may need to thin the plant to allow air and light to reach the interior of the plant. Do that right after it blooms.
As far as special winter protection for the bigleaf hydrangea, if you have steady snow cover it may be sufficient to mulch and provide good winter wind protection. If snow cover is not reliable, enclose the plant in a burlap wrap and fill it with a nonpacking insulating material such as dry straw or oak leaves. Top that with a plastic sheet or tarp to keep it dry, but allow gaps on the sides for air circulation. Put this in place in late fall after the plant has gone dormant and remove it in spring so the plant can wake up naturally with the season; be prepared to protect it from any late frosts however.
If you are not certain what type of hydrangea you have, ask your retailer where you purchased the plant. Good luck with your new shrubs!
Q&A Library Searching Tips