The giant blooms from hydrangeas pack a punch in the garden during the summer and fall, commanding attention from all garden goers. As we currently deal with frigid temperatures, it raises the question: How cold is too cold for hydrangeas to survive the season? Mastering the art of winterizing hydrangeas has become essential for any gardener seeking to preserve their vibrant blooms for the following gardening season. Here, we'll break down hydrangea cold tolerance by type, how to tell if your hydrangea has cold damage, and how to protect your hydrangea so they bloom prolifically come summer.
What Cold Temperatures Can Hydrangeas Tolerate?
Bigleaf hydrangea, oakleaf hydrangea, and mountain hydrangea bloom on old wood and have robust root systems, meaning the shrub itself can withstand some harsh winter temperatures down to -15°F, but the dormant flower buds of the canes may be compromised. So, while the shrub itself may be able to endure cold temperatures, a late-season frost or an especially harsh winter could hinder its flowering ability for the remaining lifespan of the shrub.
Hydrangeas that bloom on new wood, like smooth hydrangea and panicle hydrangea, are in a much better position, as any damage from a late-season frost can be pruned off without sacrificing the flowering ability. These hydrangeas can also withstand temperatures as low as -30°F and strong winds, making them an excellent choice for gardeners down to zone 3. The benefit to these hydrangeas is the ability to prune off old canes that may have been damaged late fall, leaving new wood to form and develop flower buds that will bloom come next summer.
How To Tell If Your Hydrangea Has Frost Damage
Hydrangeas are eager to begin their beautiful blooms, with dormant buds starting to emerge in late spring or mid-summer. Unfortunately, a late-season frost or a warm spring can severely hinder the flowering power of your hydrangea after they begin to develop these buds potentially eliminating all flower blooms for the rest of the season. If flowering has already started and temperatures suddenly drop below 32°F, your hydrangea's flowering power could be impacted. Look out for these key signs of frost damage if you got hit with an unexpected cold front:
- Leaves may appear wilted and begin to turn a red or purple color.
- Dark brown/black leaves and buds that are crispy and dry.
- Dried and blackened flower buds.
How To Prevent Winter Damage
There are some easy tips and trips to protect your hydrangeas if they are susceptible to severe winter damage. One of the first is to add a hefty layer of mulch, about 8-12 inches, at the base of your hydrangea during the late fall or after the first freeze. This helps regulate the root environment and can prevent drastic changes to soil temperature. If your hydrangeas are in the ground and temperatures dip below 0°F, it would be a good idea to wrap or cover them to protect them from the cold. While this isn't always necessary for colder, more hardy types of hydrangeas, this could minimize the risk of damage.
If you are growing hydrangeas in containers, bring them inside after the flowering season as soon as temperatures dip below 45°F degrees. Place them in a cool, unheated, dark, and dry place like a garage, basement, or mudroom. If this area stays cool, doesn't freeze, and gets occasional watering, they should be healthy and dormant until spring. As temperatures begin to rise, begin to slowly get your hydrangeas acclimated to warmer temperatures by placing them indoors in direct sunlight during the day in a process called hardening off.
While the type of hydrangea may determine its ability to flower after cold temperatures, some cultivars were created to be exceptionally hardy in areas with brutal winters. View our collection of cold-tolerant hydrangeas HERE.
