You are on the borderline for hardiness issues with bigleaf hydrangeas, so I'd be reluctant to confirm overwintering one in a container, unless the container could be moved for winter protection. Possibly one with extreme hardiness like Endless Summer (Z4) or the very hardy H. arborescens.

Colored flowers are limited to the bigleaf hydrangeas (H. macrophylla) and the serratas (nearly always lacecaps) - otherwise you get white, but often with tones of rosy pink as they age. Encouraging bluer flowers on the bigleafs requires acid (not alkaline) soil and avilability of aluminum.

Personally, I'd shoot for attempting to get a bigleaf cultivar to overwinter first before I attempted to alter color. Otherwise, Hydrangea arborescens ('Annabelle') is extremely cold hardy and might just work in a container without winter protection.

I think you would need to overwinter the entire plant in the pot in a garage or somewhere warmer.

thanks!

My mom and I each have big, gorgeous Endless Summer hydrangeas that do great in their pots. We both bought ours last summer, and they not only survived the winter (with our Oklahoma ice storms and temps in the teens), but grew bigger and have more blooms this year. I highly recommend this variety, and, if I were you, wouldn't mess with the other bigleaf varieties that only bloom on old wood, and will therefore not have blooms the following year if they freeze. That's just my opinion, though! The Endless Summer bloom for months at a time here in OK.

As was mentioned before, blue hydrangeas do require aluminum sulfate to maintain their color. This can be hard to find, but we finally found it at a farmer's grain store where other fertilizers and chemicals are sold. It can also be ordered online. Be careful with the amount you put in, though, especially in a pot, as aluminum sulfate is very strong and can kill the plant. With the right amount, however, your hydrangea will be a gorgeous blue! There's just nothing else in nature like blue hydrangeas.

I don't know how hot it gets in NJ, but remember to give your hydrangeas morning sun, and shield them from afternoon heat.

Good luck and happy gardening!

-bluehydrangea

bluehydrangea, I believe that there is a huge difference between Oklahoma and New Jersey in terms of the climate, so you can plant a hydrangea in a container. However, if we do this in zone 5 or 6 (where New Jersey is) then you will need winter protection in a pot. Otherwise, it will be too cold and severe outside.

My apologies! I was not familiar with the extremely low temperatures in Zone 5 climates. But, after I looked it up just now (wow, how do you guys deal with that kind of cold?), I have to agree with Ostrich: I would put a potted ES or any other type of hydrangea in the garage for the winter out there.

Hopefully my other info will still be helpful to you, NJmomma, if you decide to pot an ES.

-bluehydrangea

I have two very young Endless Summer plants that are about 8" tall and wide. I have them in 5 gallon containers in my shed for the winter. I'm in zone 6.
They will be protected from wind, but I'm sure it's pretty darn cold out there, shed or no shed. Should I put them in my somewhat warmer garage. It's cold there too, but perhaps not as cold as the detached shed.

Also, they get very little light in the shed. Is that an issue over winter?

I plan on watering them several times through out the winter... Will this suffice?

Can you tell me if I should do anything else / different to help them make it through the winter here in the burbs of Boston? Thx!

I would put them in the warmer location and on top of "something". Do not worry about the light. Leaves need some sunlight to do their thing but the shrubs should have no leaves if they have already gone dormant.

You could wait about 2 weeks after your average date of last frost for your city/state. Others also review the 10-day and longer forecasts to prevent having to bring it indoors again should temperatures suddenly dip a lot.