Well, point of fact, I never pruned mine. It develops what I find to be a pleasing shape on its own. It will eventually fill out by new shoots coming up from the roots and the older stems will eventually die. So...maybe pruning is mostly wasted effort ?

If I still thought I wanted to prune, i'd do it while the plant was dormant, just like most shrubs and trees.

Have you tried pinching to make it bushier?

Oakleaf hydrangeas produce invisible flower buds around July-August so you should prune (pruning is not necessary with hydrangeas if planted where they can grow to their advertised height/width at maturity) after it has bloomed but before the end of June. That way you get to enjoy bloomage for a while at least.

They are not particularly bushy shrubs, certainly not producing the same dense, mounded growth habit as say a bigleaf hydrangea. Most will appear a little leggy. And like a bigleaf hydrangea (H. macrophylla), they bloom on growth produced the previous season, so pruning without removing the flowering potential for the next season is tricky. In most areas of the country, these don't start blooming until midsummer, so pruning back after the bloom period (lasts into September in my area) will inevitably remove flowers.

One of the better hydrangea websites offers this advice on when and how to prune both macs and oakleafs (see Method 1).

I am sure I have Oakleaf Hydrangeas. Big oak leaves with drooping flowers like Hydrangea paniculata (wikipedia: http://en.wikipedia.org/wiki/Hydrangea_paniculata ) but it is budding right now and it will be in full bloom by may. the flowers turn pink later. It is a bit leggy and large (7ft?). I have lots of babies (?) underneath from my shaking the flowers under there and the seeds seem to propagate. the bark peels just like my crepe mertle or my river birch. Hmmm are we talking about the same plant? I live in Atlanta. I have never pruned it -tempted though. thank you for the web site suggestion.

Thank you for your help the website was extremely informative.

Hydrangeas in more southerly locations bloom earlier than those located further north. I would expect there to be at least a 6-8 week lag time between Georgia and Ontario :-)

May oakleafs are just starting to leaf out now. I won't see flowers until probably the end of June.