Frost damage to hydrangeas – what to do? Freezing from sub-zero temperatures?

The popular farmer’s and plate hydrangeas thrive as subshrubs. Therefore, the ornamental trees and their numerous conspecifics are considered conditionally hardy. The reason for the frost sensitivity is the partial lignification of their shoots. The twig tips usually do not become lignified. The herbaceous parts of the plant have nothing to counter winter temperatures below zero, so that they actually freeze back every winter down to the woody shoots. However, severe frost does not stop at old wood.

In the worst case, you will be confronted with hydrangeas in spring that have frozen to the ground. The concrete extent of frost damage can be determined at the end of winter. The following vitality test reveals up to which branch sections your hydrangeas have been frozen by sub-zero temperatures. That is how it goes:

• Frozen shoots are pale brown to dark brown
• If in doubt, scrape off a little bark with your fingernail or knife
• Fresh green tissue: living branch
• Pale green, dry tissue: frozen twig

Carry out the vitality test until you encounter living tissue. This way you will later know exactly where to put the scissors. If you don’t see any floral life down to the last pair of eyes, the hydrangea is completely frozen. In this case, dig up the shrub and replace it with a native ornamental shrub that will be better able to withstand a biting frost.

Cut out frost damage

Once you have determined the extent of the frost damage to the hydrangea, please do not hastily reach for the secateurs. Premature pruning can significantly exacerbate the crisis. Wait until the end of February/beginning of March. How to properly cut frozen hydrangea shoots:

• Peasant and plate hydrangeas: cut back withered flowers and frozen shoots to the first pair of healthy buds
• Ball and panicle hydrangeas: shorten faded twigs to two buds
• All hydrangeas: thin out thoroughly

The different pruning is based on the fact that peasant hydrangeas (Hydrangea macrophylla) and plate hydrangeas (Hydrangea serrata) flowered the previous year. The more extensive the pruning after the winter, the more buds fall victim to the scissors. The same applies to velvet hydrangeas (Hydrangea sargentiana) and climbing hydrangeas (Hydrangea petiolaris).

Snowball hydrangeas (Hydrangea arborescens) and panicle hydrangeas (Hydrangea paniculata) cope better with frost damage and the resulting pruning because they only create their buds during the current season. As long as at least one pair of buds can remain on the branch, you can look forward to the romantic blossom festival in summer.

Fix losses from late frost

Late ground frosts are a common scenario in regions outside of mild wine-growing regions. When winter returns in April and May after a warm, sunny start to spring, hydrangea gardeners are on the alert. Since budding and growth have already begun in all species and varieties, the consequences are fatal. If the fresh leaves hang limp and freeze to death on the branch, don’t grab the scissors right away. Slight sub-zero temperatures cannot cause serious damage to the branches. Therefore, only remove the frozen leaves and observe the development until mid-June. With a bit of luck, the affected hydrangeas will sprout again and bloom despite the late onset of winter.

On the other hand, when the ice saints come with minus temperatures of -5 degrees and colder, there is little hope for buds and young foliage. Since the frost usually does not penetrate deep into the existing wood, the blossom magic is only absent for this year on farmer’s and plate hydrangeas. Cut your hydrangeas back into the healthy parts of the branch and continue the care program as usual. By next year, the flowering bushes will have regenerated and bloomed again.

Reblooming hydrangeas, such as the ‘Endless summer’ variety line, can also cope with this setback. If the necessary pruning leaves at least one or two vital pairs of buds, the flowering bushes will try again and bloom this year. However, you have to be patient until the middle/end of August.

Tips for preventive measures

When choosing a location, consider the risk of frost damage. If the favored position in the bed and on the balcony offers sufficient protection from easterly winds and the blazing winter sun, you will rarely have to complain about frozen hydrangeas. Warming rays of the sun bring the flowering shrubs to life prematurely, so delayed ground frosts can do significantly more damage. Furthermore, we recommend the following precautions to mitigate the influence of deep sub-zero temperatures:

• Stop fertilizing after September to allow young twigs to mature
• Do not cut off wilted flower heads in autumn to protect the buds underneath
• Cover root slices in the bed and pot with leaves and brushwood before the onset of winter
• Branches covered with breathable fleece
• Alternatively, stick brushwood all around to absorb cold winter winds

Hydrangeas in pots should ideally be placed in a sheltered niche. A base made of wood or styrofoam serves to protect against frost from below. A winter coat for the pot made of bubble wrap, coconut mats or jute ribbons is also advantageous. Climbing hydrangeas protect you from frostbite with reed mats that you set up in front of the plants.

After pruning at the end of February/beginning of March, please leave the winter protective hood within reach. If the meteorologists announce ground frost by mid/end of May, put garden fleece over the branches in the evening. In harsh regions, you should be prepared for late night frosts by mid-June, when the dreaded sheep cold hits.

Conclusion
Hardly any hydrangea remains unscathed by sub-zero temperatures. The harsher the winter, the more the branches are affected. With the vitality test described here, you can determine the extent of the frost damage. With the recommended winter protection measures, you can effectively prevent devastating frost damage to hydrangeas.