Answer: Most hydrangeas are perennial but not all will flower year after year in the garden. Common hydrangeas flower on new shoots which develop on old wood so if your plant freezes down to ground level each winter, there will be no old wood on which new flowering shoots will appear. The plant will still grow lush and green, it just won't flower. It's true that blue flowering hydrangeas can be kept blue with the addition of sulfur to alkaline soils, but the amount of product you use will be small and should be applied in the early spring, before the flowers develop. If your plant is in a container it should not need treatment because the potting soil is normally acidic enough to keep the flowers blue. And, because the roots are contained in a small area, they can be burned by the application of sulfur. I think I would plant the hydrangea in the garden to see whether or not it has the strength to recover. If so, you should see new growth in the spring. Wait to see whether or not it blooms and if so, what color the flowers turn. If they are pink, you can apply sulphur to the soil the following spring to acidify it and make the flowers blue.
Best wishes with your plant!
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