WINTER HARDNESS ZONES ...

... is based on the USA system of the USDA (United States Department of Agriculture).

... refers to the mean annual minimum air temperature.

... indicates the lowest temperature a plant can withstand with a probability of at least 80%.

... depends on the duration of frost : A plant can survive a frosty night with -20 ° C without any problems,

She will not survive a permafrost of -10 ° C for 3 weeks when the ground freezes deeply.

... applies to plants that are planted out and rooted in the ground (spring planting).

... for us refers to the three-year-old wood and the wood in hibernation. If a fig begins to sprout again in the spring,

then the first shoots and leaves are by no means frost-tolerant and freeze to death at low temperatures.

In addition to temperature, winter hardiness also depends on other growth factors:

...Ground:

Plants in dry, sandy soils can withstand more freezing temperatures than in heavy, wet soils.

... water:

Too much water, waterlogged in winter or too little water (drought) reduce winter hardiness.

...Wind:

draws heat from the surface through the wind chill effect (measure of heat loss) and thus ensures evaporation cooling.

The perceived temperature is much colder when there is wind.

...Nutrient:

Reduction of winter hardiness due to a lack of potassium and excess nitrogen.

... Biotic pathogens:

Diseases, pests.

... microclimate:

can be influenced favorably or unfavorably. There can be significant differences even within a few meters

to be felt through solar radiation or shade, heat storage or cold air, sheltered or open location.

http://www.deutsches-pflanze-forum.de/images/klima_karte_gross.jpg