The cold hardiness of hydrangeas
Also marketed under their Latin name “hydrangea”, hydrangeas can be grown in pots, containers or in the ground. Regardless of how they are grown, hydrangeas generally show a good resistance to cold and it is rare for a shrub to freeze completely. But the consequences of the cold can be other:
- As they are semi-shrubs, the current year’s shoots lignify only at the base, which means that in the event of a severe winter, the ends of the stems can freeze and flowering to come to be destroyed.
- A succession of freezing nights and easterly winds can totally destroy the next bloom.
To know if you need to protect your hydrangea, it is necessary to take into account the situations described below.
The variety of your hydrangea
Indeed, depending on their variety, these plants are more or less resistant to cold, for example hydrangea arborescens or semperflorens can withstand temperatures down to -29°which is reduced to -10° for hydrangea seemanii or hydrangea macrophylla ‘Hanabi’.
The place of planting
If you live in an area where the winters are very harsh or if your hydrangea is planted in a north-facing space or in an open space exposed to the wind and the cold, it is essential to protect it.
If you have just planted your hydrangea
It is advisable to protect it during at least the first two years to allow it to take root properly and grow stronger.
Overwintering Potted Hydrangeas
In a region with a temperate climate
If you have hydrangeas in pots or containers, you can leave them outside provided you provide them with adequate winter protection. Here are some protection ideas:
- You can wrap the pot or tray in bubble wrap by doing several rounds. Then install a thick coconut mat around the entire contour and secure it securely with a thread. Make sure that it rises 10 cm above the pot to protect the roots that may be on the surface of the root ball.
- Transfer the pot or tray containing your hydrangea in a shady place, sheltered from wind and bad weather. You can, for example, put it against the wall of your house. However, remember to water it regularly so that the roots do not dry out, but moderately to prevent the water from stagnating.
- If your pot is placed on a surface such as cobblestones, you may slide underneath a polystyrene plate or a thick wooden board.
In regions subject to harsh winters
If you live in an area with rather harsh winters, it is best to bring in your hydrangeas as a precaution. Several solutions are available to you :
- The ideal is to be able to install the pot or tray in a cold greenhouse, that is, in an unheated greenhouse. It is preferable that it be in the shade to avoid the large temperature differences that could cause the winter sun.
- You can install your hydrangea in the dark in a space where the temperature does not rise above 5°. Faced with this situation of hibernation, your plant will adjust its metabolism.
- Conversely, you can choose to put it in a bright and warm place, but the absence of a vegetative state will have a real impact on the next flowering. Your hydrangea will also become more susceptible to scale insect attacks, for example.
Pruning after wintering
Once the time of heavy frosts has passed, you can prune the branches that are dead or have suffered from frost. You can shorten them to a hand’s width above the floor.
Overwinter hydrangeas in the ground
If you’re growing your hydrangea(s) in the ground, you’ve probably chosen a variety that’s right for your area. If this is the case, they generally do not need to be protected in winter, especially if the location is suitable, that is to say in partial shade and with a soil rich in humus.
For the good health of your hydrangea season after season, we advise you to mulch the ground in which it is planted throughout the year. This will allow the ground to stay cooler in the summer and warmer in the winter. In the fall, you can use a thick layer of fallen leaves and pine twigs. In addition to protecting the roots, this mulch will, as it decomposes, provide additional nutrients to your hydrangea. If bigger frosts are announced, you can cover it with a winter sail during this period.
On the other hand, for a hydrangea which has just been planted and which has not yet experienced winter in the ground, winter protection is recommended.
The most frost-resistant hydrangeas
If you want to turn to hydrangeas that benefit from good frost resistance, we recommend that you panicle hydrangea or hydrangea paniculata, hydrangea semperflorensbut also the ball hydrangea or hydrangea arborescens.
They are among the types of hydrangeas with the most high frost resistance, which means that they will not need protection in winter. These varieties form their buds on the new branches, it is enough to carry out a severe pruning in the spring. At the same time, you will remove any damage that the frost may have caused.