As the harder frosts pass in mid March its a good time to dead head your hydrangea. Most species of hydrangea do not require or are not to keen on hard pruning but removing the old flower heads will help the plant to produce flowers for the coming season. Just cut off the old flowering heads that have been overwintering. They can be used for flower arranging by handing them in a warm place once cut upside down in bunches to dry or they can be hung outside under the shelter of a overhanging porch or shed roof to provide your garden birds with some additional winter feed in the form of seeds in the hydrangea flower heads.