Glossary
Hardiness zones
The hardiness zones are a guide to help gardeners tell which plants can survive winter outdoors in a specific area. They are based on average minimum temperatures observed in that area over many years, which are classified as USDA zones.
Origin and meaning
The hardiness zone system developed by USDA, the US Department of Agriculture, is now used internationally. These categories are also used to grade plant frost tolerance in Europe, including Germany, Austria and Switzerland.
Each zone covers a temperature span of around 5.5°C. The lower the zone number the colder the climate - and the tougher plants need to be.
Table: Overview of hardiness zones
| Zone | Average minimum temperature (°C) | Plant examples |
|---|---|---|
| Zone 9 | -6.7 to -1.1 | Laurel, olive, fig (in very mild regions) |
| Zone 8 | -12.2 to -6.7 | Lavender, rosemary, grapevine |
| Zone 7 | -17.8 to -12.3 | Lilac, apple tree, forsythia |
| Zone 6 | -23.3 to -17.8 | Spruce, hornbeam, rowan |
| Zone 5 | -28.8 to -23.4 | Larch, hawthorn, small-leaved lime |
| Zone 4 | -34.4 to -28.9 | Mountain pine, Siberian alder, peony |
| Zone 3 | -40.0 to -34.5 | Arctic willow, Siberian larch |
(Note: rounded figures based on the USDA system)
Hardiness zones in Central Europe
Most regions of Germany, Austria and Switzerland fall between Zones 6 and 8:
- North German Plain: Zone 7-8
- Central uplands (Mittelgebirge): Zone 6-7
- Alpine Foreland and higher altitudes: Zone 5-6
- Wine-growing regions on the Rhine and in South Tyrol: Zone 8-9
These zones provide a rough guideline only. Local differences caused by microclimates, wind protection, sloping terrain and buildings can have a substantial impact - even within a single garden.
What this means in practice
When buying plants you will often see information like "hardy to Zone 6". This means:
- In areas with milder winters (Zone 7 or 8) the plant will survive winter without any problem.
- In colder areas (Zone 5 or 4) additional winter protection is advisable - or you might need to overwinter your plants in frost-free conditions.
Plants like rosemary, fig and chusan palm, for example, will only thrive outdoors all year round in mild areas of Southern Germany.
To sum up
The hardiness zones are a useful tool to help you pick the right plant - but they aren’t any substitute for your own observations of your own garden. Microclimate, soil, wind protection and plant care are often more important in successful overwintering than the zone number on its own.
