Answer: Your hydrangeas are probably the common ones (Hydrangea macrophylla). These plants develop flowers on new shoots that develop on old wood. So, in the early spring you'll want to cut everything down to about knee level. This will be the old wood on which new flowering stems will develop. After the flowers fade you can cut the old flower, along with some of the stem off the plant (to help keep it neat and tidy). Next spring, cut everything down to knee level again and new flowering shoots will develop on the old wood.
Best wishes with your new garden!
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