What type of hydrangeas? And where is your Zone 5b located?

Were these pots purchased at a grocery store or at a florist? Or at a plant nursery?

Florist hydrangeas (they usually just have names like: Hydrangea, Red Hydrangea, Blue Hydrangea) may not be able to handle your cold winters. Some named hydrangeas will also not bloom reliably but be root hardy there either so it would help to know the name of these hydrangeas.

They were cuttings from Nikko blue and summer endless hydrangeas. They grew really well, very healthy, dark green leafs, summer endless did bloom, nikko didn't.

Those are hydrangea macrophyllas and can be grown outdoors on the ground. Blooming is another story.. Nikko can be root hardy but to bloom reliably, it may need winter protection techniques. ES will be root hardy and is supposed to bloom on old and new wood..

But flower buds from old wood will get zapped by z5 winter (the stems will also get killeed unless there is a mild winter) so you end up with new growth every Spring. If this new growth gets old and tall enough to develop flower buds, it will produce blooms in late Summer. In some locations, some people report problems getting blooms from new growth. So, you can plant them in the ground (mulch them well 3-4" of organic mulch for example) and see how they do for you.

Hydrangeas are not happy indoors as houseplants. But they can certainly be stored indoors, especially if grown in containers, for winter protection in a cool but above freezing location. It is best if you wait until the plants are dormant or very close to it before moving inside, so bring in once most the foliage has dropped off. Light is not a concern over winter/through dormancy. The temps in your cold room should be just about right....between 35-45F.