Answer: According to the Monrovia web site plant listing, Pink N Pretty (Hydrangea macrophylla 'Monink') is winter hardy in USDA winter hardiness zones 5 through 9; it is also listed as suited to summer heat zones 7-9 which is a separate rating system. So, you should be fine. (Your zip code places you in winter hardiness zone 6A or the coldest part of zone 6 and depending on your microclimate it could actually be as cold as zone 5 just as you described.) I would suggest though that you mulch generously over the root area in late fall after several hard freezes. You may also want to provide a wind break for the plants if they are in a windy location. Do not do any pruning on these until late spring at which point you can trim off any winter damaged stems. Good luck with your hydrangeas!
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