9 Ways to Ensure Your Hydrangeas Survive Winter Freezes

Winter is coming in hot, or cold as the case may be, and it’s time to think about protecting your precious garden from freezing temperatures. Hydrangeas are cold-tolerant shrubs, some more than others, but it doesn’t hurt to give them some protection through the coldest months, especially in cold climate areas. 

The amount of protection your shrubs will need depends heavily on how cold it gets in your zone. The cold tolerance of your specific type of hydrangea is also a factor in its ability to endure. Hydrangea roots may be hardy to temperatures as low as -15°F (-26°C) or even colder. However, the tops of these plants can be susceptible to damage if they aren’t properly prepared. 

Taking a little time out of your busy schedule to prepare your shrubs for the cold will go a long way. With just a bit of extra effort, you can circumvent losing branches to freezing winds and other factors. Here are some easy ways you can ensure that your hydrangeas will make it through the winter unscathed.  

Know Your Hydrangea Type

Hydrangeas are not a one-size-fits-all group of plants. There are several species, but they don’t all have the same climate ranges. In general, species that bloom on new wood are more cold-tolerant. Species that bloom on old wood are less so. 

The reason for this is simple: the buds are not as cold-tolerant as the rest of the plant. Those that bloom on old wood go into the winter months with buds set. Very cold temperatures will wipe out the buds. The plant may survive in a colder zone, but it’s unlikely ever to bloom.

Conversely, those that flower on new wood don’t have buds to worry about during the winter. You can prune them in late winter to early spring, and they will set buds on the new growth. 

Types of Hydrangeas

If you know what type you have, it’s easy to determine how cold-tolerant it is. If you’re not sure, here is a brief guide to the different types:

Bigleaf (H. macrophylla) – Zones 6-11 – Popular ornamentals with large, showy flower clusters and large foliage. They bloom from late spring to fall and reach 2-6 feet tall.

Panicle (H. paniculata) – Zones 3-8 – Cone-shaped flower clusters bloom white and turn pink or red over time. They have great cold tolerance as they bloom on new wood.  They bloom from midsummer through fall. Larger shrubs reach heights of 8-25 feet tall. 

Smooth (H. arborescens) – Zones 3-9 – A new wood bloomer and highly cold-tolerant. Three- to six-foot shrubs produce rounded clusters of white flowers with a green tint.

Oakleaf (H. quercifolia) – Zones 5-9 – Native to the United States. The name comes from the attractive lobed foliage that resembles oak leaves. These are old wood bloomers, so they are less cold-tolerant. They produce large, cone-shaped flower clusters that open white and change to shades of pink as they mature. Lovely fall foliage. 

Mountain (H. serrata) – Zones 6-9 – These lovely small shrubs resemble bigleaf but are more compact. Lovely lace cap flowers bloom throughout the summer. Not all, but some of these bloom on old wood, making them less cold-tolerant. Choose a new wood bloomer in colder areas.

Climbing (H. anomala) – Zones 4-8 – Gorgeous vines can grow up to an impressive 60 feet long. In late spring and early summer, they produce fragrant white flowers with a blue tint that mix with smaller, fertile florets, which attract pollinators. They are well adapted to shaded areas. 

Keep Watering in the Fall

Hydrangeas are big moisture lovers; it’s right there in the name! A dehydrated plant is a weak one that will suffer cold damage more than a hydrated one. For this reason, it’s important to continue to water your shrub through the fall. 

Though they drop their leaves and go dormant in late fall, these plants still need moisture. While they won’t need quite as much, it’s important to get water to their roots until the ground freezes. Water deeply once every two weeks to keep your shrub hydrated and healthy.

If you live in a colder climate where it commonly snows in winter, you won’t need to continue to water through the winter. The snow insulates the roots. In warmer climates, however, you’ll want to water monthly, even during the winter. 

In warmer climates, winter temperatures may still be freezing. Water when the temperature is above 40°F (4°C). Don’t water hydrangeas in the evening if you expect a hard winter freeze.

Avoid Late Season Pruning

Fall is not the ideal time to prune hydrangeas. This especially applies to those hydrangeas that bloom on old wood. Pruning after they set buds will drastically reduce their flowers. Prune these immediately after they finish blooming to give them the maximum amount of time to produce those buds. 

Pruning while the weather is still mild in fall can be an issue for all types, as pruning encourages new growth. If you prune at a time when the plant is not yet dormant, the new growth it produces will be more susceptible to frost. You’ll just end up having to cut it back again in the spring, reducing the overall size of the shrub.

For species that bloom on new wood, you can prune it any time after it enters dormancy. Basically, after it loses its leaves, it’s not going to produce a flush of growth, and the old wood will be fine through the winter. I would still encourage waiting, though, as their flowers will dry on the bush and add interest to the winter landscape. 

Check for Pests and Diseases

Hydrangeas are fairly resistant to pests and diseases, but they aren’t impervious. Common garden pests can weaken your plant, making it more susceptible to the cold. This is a habit you should get into long before fall, but it’s still a good time to treat. This can mean getting off to a stronger start in the spring. 

Good pest and disease management involves proper clean-up. Make sure that you don’t leave debris and damaged foliage on the ground beneath your shrub. Before the plant loses its leaves, inspect and treat for diseases so that they won’t return in the spring with a vengeance. 

Horticultural oils, neem, and dormant oils are all good for shrubs. These oils help eliminate current pests and fungal diseases. They can also prevent future infestations by coating eggs, as some hatch in the spring. 

Stop Fertilizing

Just as pruning can encourage growth, so can fertilizer. You don’t want that new growth going into the winter because it is more vulnerable to the cold. Fertilize mature hydrangeas in the spring, just before they begin their growth phase. 

Depending on the type of fertilizer you use, you can continue to fertilize as often as monthly. But make sure you stop by early fall at the latest. Late July is a good time for the last application. 

Top Dress the Soil

Hydrangeas love compost, and top dressing in the fall will help your plant to stay strong and healthy. Compost or manure will break down slowly, giving your shrub a gentle dose of nutrients through the winter, and be present for a boost in the spring. 

Top dressing is easy. Just spread your compost or other soil amendment on the ground around your plant. The compost should extend out to the drip line to nourish the entire root system. 

Homemade compost is a wonderful substance to work on, but if you don’t have any ready, don’t worry. You can purchase compost, worm castings, and manure to use as well. These organic materials don’t cause a burst of growth the way that concentrated fertilizers will. Just ensure that any organic materials are well rotted before spreading them on your plants.

Cover Roots with Mulch

Mulch is an incredibly valuable tool for protecting hydrangeas and other garden plants from winter freezes. It serves more than one purpose and, if applied at the right time, can significantly improve your plant’s resilience to cold.

Mulch helps the soil retain moisture. As we discussed earlier, hydrangeas are moisture-loving plants, and it’s important to keep those roots hydrated going into the winter. Mulch also prevents moisture from evaporating, so it not only helps the plant but also keeps down your water bill. 

Mulch also insulates the plant’s roots. If you apply it while the soil is still warm, it will help moderate the soil temperature, buffering your plant against extreme temperature shifts.

In many places, the ground freezes and thaws repeatedly over the winter months. A thick layer of mulch will ease these transitions, keeping the soil to a more consistent temperature, which is less stressful for your shrub’s roots. 

Protect Against Wind Damage

If you garden in the upper reaches of the climate zones indicated for shrubs that flower on old wood, wind protection can make all the difference. In warmer climates, this won’t typically be necessary. If you’re in Zone 7 or lower, I wouldn’t worry as much about wind damage. 

One of the most damaging aspects of winter weather is the icy wind. If you recall, the species that bloom on old wood are significantly less cold-tolerant. Even in their upper reaches, an extra-cold winter or a cold, windy day can ruin the developing buds.

The ideal way to handle this is to plant your hydrangea in a spot where it has structural protection from the wind. However, if you have an established plant that has failed to bloom for this reason in the past, there are things you can do.

A simple covering of insulation cloth will protect your plant. If you want to go further, construct a cage from chicken wire and stakes. Then, cover the cage with frost insulation cloth or burlap, or fill the cage with leaves.

There are other, more elaborate methods of protecting your shrub from freezing winds. You can cover it with a box and wrap it with insulation. However, unless your environment has a particular issue with strong winds in winter, this may be excessive. 

Bring Potted Plants Indoors or Protect the Roots

Finally, if you have hydrangeas in containers, it’s a good idea to protect them during freezing winter weather. While they are cold-hardy, plants in containers are more vulnerable to cold. There is less soil surrounding the roots and, therefore, less moisture, which leads to less protection overall. 

If you have a protected space like a shed or garage, these will give your plant sufficient protection. Bringing it indoors or into a greenhouse is great, too. If none of those options are possible, you can insulate the container to help protect those roots. 

There are many ways to insulate your containers. You can dig a hole and sink the pot into it, which will, to a large degree, mimic planting it in the ground. This is a lot of work, though, and there are simpler solutions. 

You can construct a cage around the pot out of chicken wire or hardware cloth and fill it with leaves or another insulating material. Perhaps the simplest solution is to wrap insulation around the container and secure it in place. This is a quick and easy solution that won’t cost much and doesn’t require any digging.