Hello Louise,

Huron county is a hardiness zone 5b/6a. Assuming your hydrangeas are a variety that is hardy in your zone (see list of varieties in this article: https://ohioline.osu.edu/factsheet/hyg-1263) it should be safe to store them in an unheated garage, provided the temperature in the garage remains above freezing.

Your hydrangea’s roots generally will not survive freezing in an unprotected pot above ground in your zone. If your garage will go below freezing, you will need to further insulate the pot to improve the chance of survival.

Styrofoam insulation, bubble wrap or placing the pot in a larger container and surrounding it with mulch or evergreen branches will provide additional insulation and protection. This is a good article on winter storage of potted material: https://extension.psu.edu/overwintering-plants-in-containers

Remember to check soil moisture during storage. The soil should not be wet, but it should not be allowed to thoroughly dry out either.