Hello, oklahomarose. An "unusually cold winter" as you describe could have damaged the flower buds. You are close to Zone 5 and many mopheads cannot handle Z5 cold (ES can sometimes though). However, if that was the case, I would have expected some stems to have dried out, died and returned from the crown. And I would have expected ES to skip Spring blooming and then start blooming sometime later.

Moisture problems during the winter could have made the shrub abort the flower buds. But I would have expected blooms later on from ES.... unless you still have moisture problems??? Lord, I would hope not.

Pests like deer, rabbit and squirrels might account for some of the damage but it is hard to believe that they got so lucky that they ate all the old wood buds p-l-u-s the new wood buds from ES. Is this a problem where you live?

It would make more sense if the soil had way too much nitrogen (over-fertilized) and that was keeping them nice and green.

oklahoma, I'm not too far away from you--I'm Zone 6a Kansas--which is only 30 miles from OK. I don't know about Endless Summer hydrangeas, but I can assure you that mopheads in general have a hard time blooming in our midwestern zone 6. I'm not sure if it is that the winters are too cold or if it is those later hard freezes we often get after the spring temps have warmed up considerably, but one or both of those conditions almost ensures that most mopheads will NOT bloom in our region most of the time. I planted two shorter ones next to my porch before I knew that--5-6 years later one of those bushes managed to push out THREE blooms--close to the ground. Other than that, they don't bloom. My neighbor planted a half dozen different mopheads a number of years ago. I don't believe they have ever bloomed for her--but she does have one Endless Summer that blooms. Perhaps its earlier blooms also get damaged, but it blooms on the later buds. At any rate, hers is blooming right now, but I don't remember seeing blooms on it earlier.

As far as I am concerned, I will never again buy a mophead. I have my Annabelles for earlier in the summer, and I have a couple paniculata hydrangea (sun lovers) for the second half of the summer--some of those come in pinks. That works fine for me, but mopheads will just disappoint you most years.

Kate

I have 2 ES and 1 Blushing Bride. I planted them last summer. They are blooming fine, without any issue, and we had an extremely cold winter and a blizzard. (I am in a suburb just west of Chicago.) I did not protect them at all. One of them (BB) looked completely dead in the spring, even when ES was starting to grow (no green at ALL). They were even messed with in the spring when we had to have word done in our yard, so they were transplanted. We also had a weird spring (as usual) in which it would warm up, and then we'd get yet another freeze.

I think since ES are supposed to bloom on old AND new season's bloom (and BB new), it seem the winter should not be a problem?

I don't remember when they started to bloom, but it was about the same time, so probably the ES for me is only blooming on new wood. They are going strong right now.

Looks like maybe the overwatering or wet feet could be the issue?

http://www.ehow.com/info_7970932_endless-summer-hydrangeas-not-blooming.html

Here is a link that might be useful: ES