Since Oakleaf overwinters it's flower buds, you may be suffering from bud kill in zone 5. Is your plant in an area where it is exposed to winter winds? If you want reliable blooming in zone 5, you might have to a) move it or b) winter protect it.......yg

Interesting...I don't know much about Oakleaf Hydrangeas. I planted an 'Alice' last year and I thought it was one of the bigger cultivars with a reported mature height and width of around 12'. How wide is your Oakleaf? Would a 15' tall x 4' wide Oakleaf strike others as odd? Are you pretty sure it is an Oakleaf Hydrangea? Do you know if it is a specific cultivar or if it was seed grown?

- Brent

Whew....I totally missed that one!!...Good point Brent. 15 ft in 4-5 years in zone 5?....not likely an Oakleaf at all....yg

strikes me as odd and sure does not sound like the typical shape or growth rate for oakleaf hydrangea. that comes to about 3' of added height per year. none of mine have grown at that rate and i have never seen one that tall. they are usually wider than tall since they sucker.
are you certain it is a hydrangea? maybe a look-a-like shrub or an oak tree? ;-)

The foliage and bark look like the oakleaf hydrangeas that are for sale at our local nursery. I posted a picture in the gallery.

I purchased this plant at the Morton Arboretum Member Plant Sale so I assumed that it was not mislabeled. Actually, the label said, "Sikes Dwarf Oakleaf" which is supposedly even smaller for oakleafs. I put it in this corner because I assumed that it would get winter protection here. I've given it a couple of years to "settle in" (so I haven't really paid much attention to it for the last two years) since it was so little when I planted it and I knew it could be temperamental due to the weather, but it's really gotten away from me and grown into a plant that isn't anything like what I expected.

I went out and looked and don't even see a bud anywhere on the plant. Shouldn't it have buds set by now?

So I'm thinking that if you all think it sounds wrong, and I think it sounds wrong, it probably is not what I'd hoped to be growing here and I should just chop it down, dig out the roots and start over. Unless I've discovered a new sport of hydrangea - tall, skinny plants that don't flower. :-)

Can't tell from that picture. Can you just get a picture of a leaf or a cluster of leaves, perhaps the end of the branch?

The picture is a bit small, but I agree with others that it does not look like an Oakleaf Hydrangea. The Oakleafs that I have seen have large lobed leaves that are about the size of an adult's out stretched hand.

Here is a picture that I pulled off the Internet that shows the leaf shape with a hand for reference:

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The link below is for an image search at Google where you can see more pictures of typical Oakleaf Hydrangea plants.

- Brent

Here is a link that might be useful: Google Search Results