I live in NE Pennsylvania. You can plant your hydrangea in the ground. Make the hole bigger than the pot. Add plenty of water upon planting and do not be discouraged if the plant looks a little wilted at first. The hydrangea grows into a bush -- no need for a trellis.
The plant will die out in the winter. Come spring do not try to remove the dead stalks from last season's flowers. Often new leaves grow on them. Once the plant is in full bloom, then you can easily pull out any dead sticks.
Should the plant begin to get leaves in early spring and if frost comes, try to cover the plant. Frost will not kill the up and coming leaves, but it may mean that you will have no flowers during the summer following the frost. Flowers will come back next year. Good luck!