Are Hydrangeas Frost Resistant?
Tolerance to cold and frost varies among hydrangeas. Some hydrangea varieties are cold hardy down to negative 20 degrees Fahrenheit (-30 °C), others like the popular Bigleaf variety are especially vulnerable to frost damage.
If you’re growing a variety that’s not cold hardy in your area, you need to think about winter protection measures that will minimize the risk of frost damage to your hydrangeas.
Hydrangeas that bloom from old wood need extra protection during winter to ensure that buds survive. Those that bloom from new wood are said to have a higher frost resistance but even those can be exposed to late frost damage.
Learn how to correctly winterize hydrangeas and read my tips on what to do to help recover a hydrangea damaged by frost.
Will Hydrangeas Survive Frost?
The chances of your hydrangea surviving a frosty winter depends on its variety and cold hardiness.
Some hydrangeas that bloom on old wood are root-hardy down to -20 °F (-30°C), meaning that any damage that frost will do, will usually be superficial and other than interfering with the plant’s blooming in the next season, it won’t cause the death of the plant.
But this is not the case for all hydrangeas. Some hydrangeas can die because of freezing temperatures and cold winter winds that cause the plant to dry out. Cold weather can pull moisture from stems and leaves, causing dehydration.
A late frost in early spring can damage new growth on hydrangeas that bloom on new wood. If it’s cold enough, water in the plant’s cells can freeze, causing tissue damage that leads to parts of the plant dying.
Therefore, you must anticipate these scenarios and create a winter frost and spring frost protection strategy.
Protecting Hydrangeas in Winter
Whether it’s chilly winds or the winter frost, you must protect hydrangea shrubs from both during winter. You can start preparations in late fall when temperatures start to go down, before the first winter freeze sets in.
My method of winterizing hydrangeas includes the following three measures:
- Watering my hydrangea generously before cold weather sets in, this will protect it from dehydration caused by chilly winds
- Laying down a thick layer of mulch over the roots (you can use dried leaves or straw, I find that straw works best)
- Setting up a winter cover for the plant
The winter cover usually involves setting up a wire cage that I cover with burlap or insulation cloth. I sometimes use leaves instead. Other times I set up a polytunnel. Whatever you have handy to create a good enough insulation to protect from winds and frost.
Winter frost damage will not always be apparent. You might only notice it in March or early April when the plant is not producing any new green shoots or if the plant fails to bloom in the new season.
Protecting Hydrangeas from Spring Frost
Frost in early spring can also damage hydrangeas, so you need to prepare for that too. If you’ve set up a winter cover for your hydrangeas, don’t remove it entirely.
I remove the cover during the day when hydrangeas are no longer in danger of experiencing frost or very low temperatures, and put the cover back at night.
I remove the wire cage entirely, only when I’m sure that they’re no longer in danger of freezing, so you need to follow the weather forecast a bit more closely than you normally do.
A late frost can turn leaves purplish, it can cause wilting, or foliage along with buds can turn black and dry.
You may be inclined to prune the damaged parts immediately, but I recommend waiting a bit until you’re absolutely sure there’s no risk of another frost. Newly exposed parts after pruning can be damaged again.
To help a frost damaged hydrangea recover, add a good layer of organic mulch over the roots, water deeply and use a quality fertilizer to stimulate new shoot development.
Your hydrangeas may skip blooming this season, but they’ll come back stronger in the next.
There are a few other tips to consider when looking for ways to protect hydrangeas from winter kill. Most of these are focused on where to plant hydrangeas in your garden to minimize damage:
- Plant in a sheltered place like near a windbreak hedge
- Plant against a south facing wall
- Avoid planting in a frost pocket
Do Hydrangeas Need Frost to Bloom?
No, hydrangeas don’t need frost to bloom. As cold weather sets in in late fall, hydrangeas enter into dormancy. For hydrangeas grown outdoors, this process happens naturally.
Hydrangeas that are grown indoors, require a temperature change to trigger their dormancy. Moving them to a colder room or to the garage, where they are protected from frost, will signal to your potted hydrangeas that it’s time to enter into dormancy.
Potted hydrangeas that are kept outside during summer and fall are also at a risk of frost damage. Taking precautions can prevent damage to them too.
Potted Hydrangeas and Frost
Potted hydrangeas should be moved indoors in a cold room or your garage. The soil in small pots can freeze over quickly, so it’s best to move them inside in late fall.
Move them back outdoors in spring when the risk of frost damage is no longer a threat to them.
If you’re growing hydrangeas in large planters that are too heavy to move, you need to apply the same winter protection methods I recommended for garden planted hydrangeas.
If you create a good enough insulation and apply a thick layer of mulch over the roots, your hydrangeas should stay safe from winds and frost even if they’re grown in planters.
Hydrangeas are frost resistant to a degree. Some hydrangeas will tolerate cold temperatures and frost better than others, but correctly prepping them for winter, will minimize the risk of any serious damage.
Hydrangeas can bounce back from superficial winter damage, but not severe winter dehydration or root damage.
Because it’s easy to protect these plants from winter kill, follow my tips and recommendations, so you can enjoy the marvelous blooms of your hydrangeas every year.