We have a hydrangea that we moved from the ground to a container. Can we leave it outside all winter, or would it do better inside a garage?
—Don Stewart, Wadsworth, Ohio
Susan Cohan replies: In the ground, many types of hydrangeas can survive your USDA Zone 6 winters. But in a pot exposed on all sides, the roots will suffer more frequent freeze-thaw cycles and need to be given extra protection.
The safest approach is to move the container into an unheated garage and water the soil periodically during the winter. Put it back outside in early spring when the danger of a deep freeze is past.
But if you'd rather leave the pot outside, place it in a spot sheltered from the wind and out of the sun. There's no need to cover the plant, but you can insulate the soil from temperature swings by piling leaf mulch around the outside of the container and holding the mulch in place with burlap. Snow also provides good insulation if the pot is buried in it.
Whether the container spends the winter in a garage or outside, make sure it can survive freezing temperatures. Fiberglass, concrete, stone, metal, and wood are generally frost-proof; ceramic, including terra-cotta, is not.
Also, raise the pot off the ground to prevent ice from plugging the drain hole and turning the soil into a frozen-solid block. If your hydrangea is a reblooming big-leaf variety, like H. macrophylla 'Endless Summer,' cut the stems back to about 6 to 8 inches from the top of the pot in late fall. That will encourage the growth of new stems and more blooms next spring.
Shown: A hydrangea can survive the winter if you take steps to insulate the soil from the freeze-thaw cycles that destroy pots and kill the roots.