Macrophyllas are hardy to Zone 6. How ES does in cold zones is subject to debate. ES is advertised to be hardy in Zones 4-5 but there has been a lot of complaints in the forum from people in those zones so all I can say is to consider Zones 4-5 temps as "problematic".

The other problem that you can have is if temperatures see-saw a lot, stay warm and make the shrub begin to reawaken, just as a cold front drops by and temps take a plunge. That scenario can kill buds even though the cold temps may not get to the levels rated for Zones 4 or 5.

Options: Cover them if they appear to be reawakening (not very useful if temps go down really cold). If your soil has not frozen, water the night before and make sure you have 3-4" of mulch. You can also put some Xmas lights under the sheets. Or just winter protect them (less work than the other options) using hay or mulch.

Sometimes you can tell when plants are reawakening: the stems begin to leaf out. Sometimes you just cannot tell. Last year, I got no blooms (like you) and there was no leaf out. This year, there has been some leaf out on some plants (limited to the ends of the stems only -- but that is where the flower buds usually are).so we will see what happens. Temps have been going down gradually so I am not sure if the shrubs will go dormant again or what...

My oakleaf and paniculata hydrangeas had no issues. They and arborescens hydrangeas have less issues but see-sawing temps can still get the oakleaf and arborescens blooms sometimes.

Luis

Here is a link that might be useful: USDA Zone Temps

This post was edited by luis_pr on Mon, Jan 5, 15 at 18:34

Thank you Luis, this info is very helpful! If my local home depot still has mulch I will pick up a few bags. And I really like the christmas lights idea. The Hydrangeas are in the front of my house and they sure look ugly with out leaves and flowers.

So basically I'm looking out for temps below 0?

If the hydrangea is dormant, somewhere around that. If it is re-awakening (and sometimes one cannot tell) then you can kill the buds with higher than zero but sub-32 temperatures (it is just impossible to tell).

As I previously mentioned, this year mine did re-awaken and have new leaves at the end of the stems so when the temps hit 18 degrees Weds Night, ugh..... I am hoping that a few recent nights below 32 but in the mid to high 20s may make the shrub go dormant before the 18 degrees get here because the temps will get here and stay cold for a while. Sometimes, a dip causes some damage but it is limited if the temps then 'turn around' on the following day.

I am not planning to winter protect the macrophyllas, all of which bloom on old wood. I will see what happens. At least, if your ES flower buds die, you should get bloomage later on (or so the advertising campaign says, right? LOL!). Good luck with your shrubs.