Experts and BHG readers answer.
Overwintering a potted hydrangea inside
You will likely have more success overwintering your hydrangea by planting it outdoors and mulching it in well rather than trying to overwinter it in the basement or in the garage. The root zone of the plant is the critical part of the plant to survive. If you bury the roots, they will be insulated against temperature fluctuations. If your can maintain your garage at or just above freezing, it could remain dormant there. However, it usually warms up enough at times that new growth begins which will be killed back by later drops in temperature. At least outdoors, the plant will remain dormant all winter.