Answer: Big leaf hydrangeas such as Nikko Blue develop flowers on new growth which emerges from old wood. If your plants freeze down to ground level each winter the old growth will be dead and even though you get new growth, it will not flower. Nikko Blue is marginally hardy in your gardening zone. If you can find a garden spot that is protected in the winter (near a building, for instance) the shrubs won't die down to ground level and you will get flowers the following spring. If you can't move your shrubs, consider making cylinders out of chicken wire (or hog wire) to place around each plant and fill the cylinder with fallen leaves or pine boughs to provide some winter insulation. Just cut the plants back to about knee high after the first hard frost of the season, set the cylinder over the branches and stuff leaves or straw or other insulating material in and around the branches. This should help the old wood survive and the following year you should get flowers. Best wishes with your hydrangeas!
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