when should you prune hydrangeas

I can't offer any personal guidance. My climate is pretty different, obviously, but your NC cooperative extension folks have this nice summary: http://www.ca.uky.edu/hla/dunwell/hydprun.html Here is part of his recommendation: "My advice with these is to do what you feel like doing when it comes to pruning. If cautious, prune by only removing some growth each winter. Since most of these shrubs don't seem to demand pruning in order to be attractive, don't prune unless the plants really call for it. In the mountains of NC, after years of observing over a hundred cultivars of macrophyllas, I am convinced that when plants fail to flower in our fields it is usually due to a late frost killing new growth and a slow recovery."

I agree completely that hydrangeas are often overpruned. You need to know what kind of hydrangeas you have, Robyn, but if you mean the mopheads with big blue or pink blooms, it is important to remember that they bloom on buds set the previous year, so you should prune them right after they finish flowering.

I have a guide to pruning all types of hydrangeas here: http://www.walterreeves.com/landscaping/hydrangea-identification-and-pruning/

Walter's hydrangea pruning guide is an excellent summary. I am getting concerned because two of the hydrangeas closest to our house are already showing signs of leaf break for new growth. I may be pruning out cold damage before this season is over.