Answer: There are lots of varieties of hydrangea. Some are winter hardy in your growing region and some are not. I think your hydrangea is a Florist's Hydrangea (Hydrangea macrophylla). If so, it won't bloom if you plant it outdoors. This is because these types of hydrangeas produce flowers on new shoots which develop from old wood. In your winter climate all the wood will die down to ground level, leaving no old wood on which new flowering shoots can develop. I would plan on keeping the hydrangea indoors during the winter months and outdoors on a porch or patio in spring and fall. By the way, the flowers are huge because the plants have received special care in a greenhouse. Growers manipulate lighting, temperature, fertilizers and growth hormones to make hydrangeas bloom at specific times. The same plant under normal growing conditions would have reasonably sized blooms but nothing quite as spectacular as your plant has now.
Best wishes with your hydrangea.
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