I understand how intimidating the 'experts' can be on the subject of pruning. Old wood, new wood, pruning groups, yadda yadda yadda. But in the home landscape, it's hard to imagine how you can go wrong if you follow one simple rule of thumb: Prune immediately after bloom (I'm sure there is at least one 'expert' out there that will take exception). In the PNW, right now is prime hydrangea bloom time (my mophead blooms are just beginning to color and my Paniculata's buds are just beginning to swell). So if you prune now, forget about next season's blooms, you'll miss out on the best of *this* season's blooms. Wait until the blooms begin to fade, and while you are deadheading, go ahead and prune the shrub if you really must. Mopheads and lacecaps never 'need' to be pruned except to remove deadwood or to improve appearance, and you should not be pruning any hydrangea to try to control their size. If your hydrangea is too large for the area it is in, transplant or remove it and try one of the smaller cultivars. Having said that, you can improve the appearance of a hydrangea by removing dead branches and any branches that are crossing or rubbing. Simply doing that can reduce the bulk of the shrub significantly. If you do prune it, stick the live cuttings in a pot of soil and grow them to share with friends and family - or take them to a plant trade - I'm having one in Olympia on Sept. 15 (see my posting on the PNW Exchange forum at the link below), and someone is talking about having one in October, and there's the Green Elephant trade in November. Hydrageas are very popular at trades - The ones I grow from cuttings always get snapped up immediately.

Here is a link that might be useful: Sept 15 Olympia Fall Trade

The year we bought our house it cut back a hydrangea that was crowding a walkway when we closed in late September . The next year the area that I cut back had fewer blooms than the rest but otherwise the plant was robust and happy.

Just to simplify.......:-) The hydrangeas that produce the big colored mopheads or lacecaps (H. macrophylla or serrata) bloom on growth that was produced the previous summer, with a few exceptions. Same for oakleaf hydrangeas. Pruning these in our long blooming season can affect flower production the next year - those flowers buds have already begun to be formed.

That said, if you are willing to forgo a bloom season or a reduced bloom, you can prune them back as desired. Late winter/early spring is the recommended time as it is easiest to determine dead wood and winter damage from healthy growth. Or you can undertake a rejuvenation program by cutting back a third of the oldest canes/stems to the ground at that time. This has the advantage of maintaining a decent bloom season, increasing the vigor of the plant by stimulating new basal growth but still reducing overall size, albeit over a period of years and on a temporary basis. That shrub will grow back to its intended size.

Panicle hydrangeas and the Annabelle types bloom on the current season's growth and can be pruned as desired, again best in late winter/early spring before growth begins in earnest. And deadheading - removing old, faded flowers - on any type of hydrangea can be done at any time. Just cut back to the next set of leaves under the flowerhead.