Answer: You must be refering to Hydrangea arborescens (Smooth Hydrangea). Many other species of hydrangeas would not be hardy in your region. In your region it is best to treat this plant as an "herbaceous perennial"; that is, one that essentially dies back to the crown and regrows each year.
In late winter, cut back the plant right to the ground and fertilize lightly. Although cutting back like this should produce a sturdy stem, there is really nothing you can do to keep the flowers from weighting down the branches. You can, however, use them as cut flowers, or dry them for use in dried bouquets. To dry them, simply cut the flowers at the base when they are fully open and just beginning to fade, strip off the leaves, tie them in a bunch, and hang them in a cool, dry place.
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