Winter hardiness zones

Winter hardiness zones for plants in Europe

The map of hardiness zones for plants in Europe was developed by W. Heinz and D. Schreiber (Released in the German Dendrological Society No. 75) and first published by Bärtels, A., ”Gartengehölze“ for the publishing house Eugen Ulmer, Stuttgart. On our website you will find the hardiness zones of each plant at the end of the description.

Basis

Basis of the hardiness zones are the annual average minima of the air temperature.

Temperature ranges

Temperature ranges for Europe are 11 zones with temperatures declared by 5,5˚C. In Central Europe only the zone 5 to 8 are occurring. Their division into half-zones takes into account the relatively small scaled Central European climate.

Mapping

The mapping in a hardiness zone gives you evidence of the coldest thrive mostly also in the warmer zones. It can be assumed that trees and shrubs have a survival rate of 80 percent in their specified hardiness zone, in the next following warmer zone the survival rate is increasing significantly.

Local climate

Each zone of the map shows the average hardiness of the winter. Within each zone are many local climatic variations. Close to buildings, in particular the urban development, as well as a protected southward hillside, creates much milder conditions. However, hollows, valleys and northern hillsides are less favorable and can get the effect of at least a following zone.

Rivers

In valleys there are relatively mild sections, if the water will be not frozen because of industry influence, heated streams or fast flowing rivers. This heats up the air in cold winters and generates fog, which reduces the further cooling by radiation. Such local climate deviations have mostly the effect of a half zone level.

Extreme

In extremely cold winters, where the average annual minimum of the air temperature drops significantly, more sensitive trees are endangered. Through the choice of right local climate locations and winter protection frost damage can be prevented or reduced.

Frost

Frost hardiness is a hereditary property, but within the genetic variability it is shaped by the locational factors. That includes special soil conditions and the supply of nutrients as well as the weather development in the autumn and winter.

Weather history

A dry autumn encourages an early stop of growing and the ripe off. A warm and very rainy autumn, especially if it lasts long causes the opposite. A gradual increase of the cold stimulates the winter hardiness. An early first night of frost stops the growth and serves the winter-hardiness. But deeper freezing temperatures are very dangerous in this period and damages can be seen only in the following spring.

Continental climate

In continental areas the woody plants get during the vegetation period a higher sum of heat as in maritime Areas. The plants are ripe off more safe, what develop their winter hardiness.

Temperature change

Continental climate is characterized by greater temperature extremes; where native plants are therefore quite frost hardy. The same species are losing this property in the maritime climate, where they tolerate far less deep temperatures. They are especially sensitive for a multiple change between frost and warm periods.