1. The danger comes from scenarios like these: (1) l-o-n-g periods (several days or weeks) of very, very cold temperatures that are unusual for your zone, such as you having Zone 4 cold temperatures or (2) wildly fluctuating temperatures. Wildly fluctuating temps means having long periods (several days or weeks) of unusually warm temperatures that last enough to force the dormant plants to âÂÂawakenâÂÂ; then as the plants begin to "awaken", the warm temps are very quickly replaced by low temps that stay cold long enough to cause damage to the flower buds.

The first scenario usually occurs during the winter months; it would be very rare but not impossible for temps to tank to Z4 levels in Z6b in the Fall for example. The second scenario can occur at any of these times: late in the Fall, anytime in the winter and in the early Spring.

In last year's winter, we had over 24 of these wild fluctuations before year end. As a result, I had very few blooms. However, I should note that the problems that I had were always with mopheads; the oakleaf hydrangeas were not affected. They are winter hardy to Z5 but wild temperature fluctuations could cause problems. So, knock on wood!!!!!

2. Knowing when the flower buds are vulnerable can be difficult since -usually- you really have no visible way of knowing that the plants are either becoming vulnerable or are vulnerable. Obviously, if the plant starts leafing out in winter, the flower buds are vulnerable. But, sometimes you do not âÂÂseeâ any visible signs.

This year in an example of âÂÂearly leaf outâ over here. The mopheads have leafed out (only on the ends of the stems). That tells me that the mopheads flower buds could get wiped out again if a sudden drop to the low 20s (or less) comes aaaand stays cold for a while. It is hard to say whatâÂÂs up with the oakleafs. They finally went dormant about 2 weeks ago and their leaves dried out but they could now be in a state were they are âÂÂawakeâ but have not leafed out.

Last year was an example of the other scenario: I had no visible signs that any hydrangea was breaking dormancy. The mopheads did not leaf out and yet they had no flowers. The oakleaf hydrangeas did not leaf out and they had flowers in the Spring.

So, I am hoping that temps will slowly/gradually get cold, the plants will go dormant again with no damage to the flower buds. So far, the long term forecasts are not worrisome but stay tuned. You may want to go to weather.com and look at your 10-day forecasts.

To help them all, I water the night before cold temperatures hit (if the soil has not frozen) and I make sure that they have 3-4" of mulch. If it snows, I do not remove the snow since snow helps protect the shrubs' roots. If you are concerned, consider winter protecting them as soon as you plant them on their first winter. Or keep them in a garage or shed during the winter and plant them in the Spring (water...

samnsarah, I hope your oak leaf hydrangea(s) are doing well. I'm NE KS, zone 6a, near 5b. I planted 3 hydrangeas on the north side of my house last summer. The other 2 (I think they're Quick Fires) are leafing out nicely, but the oak leaf I planted is not. I have other, established hydrangeas, and they're all showing a little foliage. I know we've had a very late spring, but I'm concerned. Has your oak leaf leafed out? If so, when?

I live in a rather unpredictable, nasty climate. It took 3 years before our newly planted Oakleafs actually bloomed. Last year was the first year and I was so happy. I do find them to be slow growers as well. We have never covered them in the winter.

I planted my Alice last year in spring. It survived a decent winter with coldest being -2F. This spring we had the last freeze on April, 15. I did not cover or protect it all. And here it is now surviving 100+F

Yay! I followed a previous suggestion and waited till the end of May before pronouncing mine dead, dead, dead.

What was the variety that died?

ksmetamaid, yes my oakleaf already leafed out and it now is full of blooms. It's doing very well, but every year I have to spray it with neem oil, because every year it gets brown spot on it.

In answer to my own question: I have not covered my oakleaf hydrangeas once, and so far the flower buds have not been damaged by frosts or late freezes even though we have had them. Perhaps that is because the flower buds don't really develope enough to be affected by a freeze until all danger of freezes has past, which in zone 6b is approximately May 10.

Here is a photo of my Ruby Slippers Oakleaf Hydrangea. The flowers are just beginning to turn red.

Very nice. Similar to mine down here but yours appears larger. I just wish the pinks were stronger as it is more greenish... with a tad of pinks here and there.