Glossary

Hardiness describes how well a plant can survive frosts and wintry weather without suffering damage. It’s dependent on genetic factors, origin, location and weather patterns – and it’s a key factor in choosing plants for your garden.

What does hardiness mean?

Hardy plants can cope with low temperatures because they adapt to the cold:

• They pump water out of their cells to prevent frost damage. 
• They create antifreeze compounds like sugars and proteins to help prevent freezing.
• They radically slow their metabolism to conserve energy.

These strategies enable them to survive cold spells without cell damage.

Hardiness zones

In Central Europe, plants are graded using the hardiness zones (USDA zones) which indicate the lowest average minimum temperatures a plant can tolerate:

• Zone 8: to –12°C (e.g. lavender)
• Zone 7: to  –17°C (e.g. fig, rosemary in mild regions)
• Zone 6: to –23°C (e.g. apple tree, lilac)
• Zone 5: to  –29°C (e.g. spruce, rowan)

Most regions in Germany fall between Zones 6 and 8. These categories can be a useful guide – but they don’t take all location factors into account.

Key factors

In reality a plant’s hardiness will depend on various factors and conditions:

• Location: Wind, ground moisture levels and sunlight will affect frost tolerance.
• Soil conditions: Waterlogging weakens roots and makes plants more vulnerable.
• Plant health: Diseased or stressed plants are less resilient.
• Weather patterns: Alternating frosts and thaws can be more dangerous than persistent cold weather.

Young plants in their first winters are also generally more vulnerable than older, established specimens.

Fully hardy, frost hardy, or half hardy?

• Fully hardy: survives Central European winter outdoors without protection.
• Frost hardy: tolerates brief frosts, but needs protection during extended cold spells.
• Half hardy: can stay outdoors in mild regions but best overwintered in frost-free conditions elsewhere.

Example: rosemary is hardy in mild locations but vulnerable in areas with harsher climates.

To sum up

Hardiness isn’t a fixed attribute but the product of multiple factors. By factoring in location, planting time and protective measures you can successfully overwinter even your more sensitive plants – for a garden that’s full of life all year round.