The winter hardiness of a plant is its robustness enough to survive a winter even with prolonged frost and adverse weather in the respective climatic region. In addition to the cold stress for the plant associated with low temperatures, drought, wind load, frost, sudden drops in temperature and the course of the soil temperature also play a role.
The term is mainly used in horticulture for plants that are grown outside of their natural range.
- The related term frost hardiness , on the other hand, deals with the influence of temperature on plants in their natural or breeding environment.
For the winter hardiness of plants
The temperature specifications for winter hardiness can vary greatly. Some of them relate to the general survival of the plant, but not to all parts of the plant that may be damaged or die. Geographical parameters for the area of origin of the respective plant, such as the climate and vegetation zone , prevailing winds and the altitude of the natural range, are also decisive . These parameters are all the more important the more they differ from the climate in the area of use.
As a concrete measure of hardiness are available for garden owners the Hardiness Zones (WHZ). In Germany they range from 5b (cool, Alpine region ) to 8a (warm, Rhine rift valley ). A recommendation for the corresponding winter hardiness zone can be given for each plant species. In Bavaria there are also cool locations outside the Alps, for example with WHZ 6a near Rosenheim , Amberg and Hof . The warmest regions with WHZ 7b to 8a are on the Untermain .
But this classification is only a rough guide. The respective microclimate is more decisive for winter hardiness . Because even in cooler regions, plants sensitive to the cold can develop well in a protected location. Protection from cold east and north winds in particular increases the chances of survival in winter considerably. For example, a chain of hills , a hedge or a house wall cause noticeably higher temperatures at the location - one reason for the traditional trellis (especially for pears , apricots and peaches ) on the south side of farms .
“Winter hardiness” in other contexts
The word is also increasingly finding its way into everyday language, where it doesn't just refer to plants. The terms hardy and hardy are used almost synonymously, although the first term refers exclusively to plants and the second to inanimate. For example, a grave is made winter-proof by the cemetery nursery by simply leaving hardy plants and covering any vacant areas with fir branches.
Even structures in the open air ( retaining walls , paths, cisterns, etc.) are now often referred to as hardy if they withstand severe frosts. More precise technical terms for this, however, are frost depth and penetration depth as well as frost protection and frost resistance .