Oakleaf hydrangeas, like H. macrophyllas and serratas, develop invisible flower buds in July-August (July for me in the South and August-ish for you in the North) near the ends of the stems. These buds stay on and open in the Spring when you then get blooms.Since the stems that you have now grew from the base this year, the plant has not had time to produce flower buds until now. The flower buds that it has developed (or is developing) will open in Spring 2017 if the stems do not get killed by winter.

Because flower buds develop during July-August, any pruning that is needed should occur after it has bloomed but before the plant develops flower buds in July-August.

If you prune an oakleaf stem now, there is a chance that you will be cutting off the 2017 Spring blooms. Because oakleaf hydrangeas are hardy to Zone 5 and you are in Zone 5, I would suggest winter protecting to make sure that the flower buds and the stems are not killed during the winter months.

I personally prune in late June when needed. That way, I get to enjoy the blooms
as long as possible. Being further in the north, you can probably wait to prune until mid-July or the start
of August. This can vary every year so play it safe and maybe do it
in early to mid July.

With all growth originating from the crown now, consider your plant as if it was 'newly planted' and expect some
branching later. Be aware that pruning of hydrangeas is typically not
needed unless you have some safety issue, dead stems or the plant is in a small location where it does not fit (in that case try to transplant it elsewhere so you do not have a yearly pruning chore). Except for removal of dead wood or minor aesthetic issues, I normally do not prune any hydrangea.

I had one Alice that died due to root rot during an El Nino Year that dumped lots of rain in my yard and forced me to get a landscaper to fix drainage issues. I now replaced Alice by smaller oakleafs. Enjoy your Alice!

I was probably not clear enough. LAST year it was killed
almost to the ground. THIS year, I had about 18” of live stem when I took the
winter protection off. It had been completely covered all winter. It had leaf
buds along both the sides and the tip when I uncovered it, and it soon leafed
out. There was no die back at all, and I did not trim anything. (THIS winter will be very challenging, as I
need to cover a 5 foot tall skinny stem! I have no idea how I will do that.)

But if flowers are produced on old wood – and I did have 18”
of old wood – I still did not have any flowers. That is part of what has
confused me. I kept thinking I should prune the stem to induce branching, but
was waiting to see flower buds first, so I could prune after; and never saw
any.

I first got interested in oakleafs after seeing some in bloom at the Missouri
Botanical garden in St. Louis. (One zone warmer than me). Though that was in early
October, and everything I have since read seems to indicate that they bloom in
early summer.

Since I have only the 2 stems, where does it produce flowers?
I assume only at the tips, not along the
sides? If so, I will have only 2 flowers next year: assuming I can keep those 2
tips protected from dying over the winter.

Yes, flower buds are produced on old wood but they are not surviving. Typically this mean problems like the flower buds is not surviving winter (so it needs winter protection), it is not getting enough moisture after it develops the buds (so the plant then aborts the buds) or deer ate the flower buds). Branching will not help produce blooms under these scenarios.

It should produce blooms at or very near the ends of the stems.

Hi Linnea, is it possible to bend the branches to the ground without breaking them...put a rock or something heavy on them and bury in leaves,I have done this with my ES, the branches will come right back

Another option might be to take a old barrel,cut the bottom out turn it over fill with leaves