Healthy neighbor #1:

All else being equal, the trouble is likely in the roots. Only way to know is to lift it out. It looks well enough to wait until early, early next spring to check it out. Has it gotten any better or worse since planted?

tj

If it leafs out later (or more slowly) than others and the leaves look normal after their unfurling and enlarging process is complete... such that, its leaves end looking like the leaves of the other oakleaf hydrangeas, I am not sure I would worry. My macs do not all start to leaf out at the same time, speed or rate.

Like tsugajunkie said, it may be a problem with the roots, it may be normal or it might be getting a winter injury that the other shrubs are not getting somehow. For example, I have one oakleaf that leafs out later and has more blooming issues (winter-related problem) than other oakleafs which are in a more protected location. Or ... it may be kind of early for this but... you could check to see if there are any signs of pests like mites that can produce distorted leaf growth. But I am not sure I would consider what is in the pics as distorted though, just very young and still opening leaves. Or maybe I need new glasses! Ha!

It has grown some in the last 3 years snice it's been planted. Once the leaves unfurl, it seems healthy enough but it has never bloomed. There is one behind it that is a year older that is normally covered in blooms. Of the 2 "neighbors" I pictured, 1 bloomed well last year. The other grew a bunch but didn't bloom. Both neighbors have flower buds already this year.

If the one that's slow to wake up doesn't bloom this year, I may lift it as suggested next year to look at the roots.

That just sounds like a winter injury that has killed the flower buds. I have one oakleaf (a Ruby Slippers) that has done the same thing too for the last three years in a row. But a nearby planted PeeWee and Snow Queen shrubs had no issues.

The problem is mild winters. When the plant is subjected to mild winter conditions, it does not make fully go dormant and exposes flower buds to the vagaries of winter. When a big temperature drop finally happens (say, from the 70s to the 20s), the flower buds are not well protected, get zapped and the shrubs produce no blooms.

Try some winter protection to prevent bloomage issues when you have mild winters with large temp fluctuations. Also, make sure that the soil does not go dry during dry winters. If your winter is dry and the plant is not fully dormant, it could easily abort flower buds when it senses dry soil. It also helps to water the night before a big drop well below to the freezing mark.

You could water it once every 2-3 weeks or when a finger inserted to a depth of 4" feels dry. Watering is no longer needed once the soil freezes but you do not get that in Z8.

This type of winter injury can occur randomly to several (or just one) plant in an area so I would not be surprised that only one was affected. Since the problem happens often, I would winter protect it; or transplant it to a more 'protected' location.