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Hydrangeas are among the flowering shrubs that can be cultivated both in the tub and in the bed - however, some species require winter protection in both cases, at least in cold regions, or should be overwintered frost-free. This concerns especially the newer varieties of the peasant hydrangea (Hydrangea macrophylla) and the plate hydrangea (Hydrangea serrata). They are increasingly regarded as potted plants and often even as houseplants - therefore, the frost hardiness is no longer among the priority breeding objectives. However, the old garden species are also slightly sensitive to frost, because these two species are so-called shrubs - this means that this year's shoots only lignify on the base and can largely freeze from the flower-studded shoot tips in cold winters.
Wintering of pot hydrangeas
If you cultivate your hydrangeas as potted plants, you can overwinter them with a corresponding winter protection in a sheltered field in the field. The planter is first wrapped with several layers of insulating bubble wrap and then wrapped in a thick Kokosmatte. Then fix the mat with a string. Make sure that it protrudes about ten centimeters over the edge of the pot and then cover the surface of the root ball with autumn leaves. Place the prepared hydrangea in a shady, wind- and rain-protected place directly on the wall of the house. If the pot stands here on a paved surface, it also needs insulation from below. You can just put it on a polystyrene board or on a thick wooden board.
Pot hydrangeas are overwintered with a well-planted planter in a sheltered spot in the garden
Note that the hydrangeas in rain-protected places occasionally need to be watered in winter, so that the roots do not dry out. If the flowering shrubs freeze above ground, this is no problem for most modern varieties. They float well from below and then form flowers on the new shoot buds in the same year, so you do not have to do without the splendor.
For those who live in a winter-cold region, pot hydrangeas should prefer to spend the winter in the house. The optimal winter quarters is a so-called cold house, ie an unheated greenhouse. It should be well shaded against the winter sun, so that the temperature fluctuations are not too big. In principle, a dark hibernation is possible, but then the temperatures should not exceed five degrees, so that the hydrangeas largely adjust their metabolism. Although a bright, warm wintering is also possible, but not optimal - so the bushes are easily infected by sign lice. In addition, the lack of rest inhibits the formation of new flower buds.
A pruning of the frozen or dead old flower shoots takes place only in spring, when the deep frosts are over. Remontant varieties can be shortened like shrubs to about a hand's breadth above the ground.
Winter protection for outdoor hydrangeas
In winter-mild regions, older peasant and plate hydrangeas planted in the garden generally do not need winter protection - provided that they have a species-appropriate location in partial shade on humus-rich soils. In the continental climate, as it prevails in East Germany, for example, you should mulch the bushes in autumn with a thick layer of leaves covered with fir-brushed rice. In addition, you can temporarily cover the crowns with winter fleece in case of persistent severe frosts. Older varieties of peasant hydrangeas and plate hydrangeas do not remount, so flowering often ceases for a year after severe frost damage. For newly planted hydrangeas, which have not survived winter in the field, winter protection is generally recommended.
These two species are hardy: panicle hydrangea (left) and ball hydrangea (right)
The largest frost hardiness show panicle hydrangeas (Hydrangea paniculata) and ball hydrangeas (Hydrangea arborescens). They get along without any winter protection. Since these species plant their flower buds only on the newly formed shoots, the old flowering shoots are cut back strongly in the spring and at the same time any frost damage is removed.