USDA Hardiness Zones — how to find your zone

Before you buy a shrub or perennial, one question is worth answering: will this plant survive winter where I live? The simplest, globally recognised tool for that judgement is the USDA hardiness zone. This guide explains what zones mean, how to find yours, and how to choose plants safely on that basis.

What a USDA hardiness zone is

A USDA zone is a simple indicator based on the average annual minimum winter temperature of a location — that is, how cold the coldest night gets in a typical year. The scale was devised by the US Department of Agriculture (USDA), hence the name, but it has become a common language for gardeners worldwide.

Each zone spans about 5.5°C and is split into two halves — “a” (cooler) and “b” (warmer). A few zones relevant to our climate:

Zone	Average winter minimum
5a	−28.9 to −26.1°C
5b	−26.1 to −23.3°C
6a	−23.3 to −20.6°C
6b	−20.6 to −17.8°C
7a	−17.8 to −15.0°C
7b	−15.0 to −12.2°C

The higher the number, the warmer — a zone 7 plant is less cold-hardy than a zone 5 plant. Nurseries and plant atlases usually quote the lowest zone in which a species overwinters in the ground without protection.

How to read the range on a plant card in the atlas

Every plant card in our atlas shows an indicator in the form “USDA min–max” — for example USDA 4–8. Beside it is an “i” icon that opens a popover with an explanation and a schematic map of zones for Poland, Germany, the Czech Republic, Slovakia, the USA and Canada. If you allow geolocation, the map will try to highlight your approximate region and zone.

Read the range like this:

• min — the lowest zone in which the plant safely overwinters in the ground. This is the number that matters most to you.
• max — the upper limit above which the climate may be too warm for the species (mainly relevant for plants that need a cold winter to set buds).

The hardy English yew or Norway spruce, for instance, have a low minimum and cope almost anywhere, while the saucer magnolia needs a milder zone and a sheltered spot.

Finding your zone

To choose plants, you need to know your zone. Rough values for Central Europe:

• Poland: roughly 5b–7b. Coldest in the mountains and the north-east (locally 5a or lower); warmest in the west, along the coast and inside large cities, where buildings create an “urban heat island” and push the zone up to 7b.
• Germany, Austria, Switzerland: highly varied. Western German lowlands can be warmer (7a–8a), while the Alps and high valleys are much colder (4–6).

General rule: the higher the altitude and the further east/north-east, the cooler the zone. Cities are usually half a zone warmer than the surrounding countryside.

How to match plants to your zone

The rule could not be simpler:

A plant will survive winter if your zone is equal to or higher (warmer) than the plant’s minimum.

So if you live in zone 6b, you can safely plant anything with a minimum of 6b or lower — such as 6a, 5b, 4. Plants with a minimum of 7 or 8 become risky without extra protection.

A few forgiving, broadly hardy plants: common juniper, English lavender, panicle hydrangea or rhododendron — all thrive in typical Central European zones, though the rhododendron also needs acidic, moist soil.

Microclimate — your garden isn’t uniform

The zone on the map is an average for the region, but conditions vary within a single plot — these are microclimates. They can shift real hardiness by half, even a full zone:

• Warmer: against a building’s south wall (the wall radiates heat), in spots sheltered from wind, on high ground (cold air drains into hollows).
• Cooler: in dips where cold air pools (“frost pockets”), on open, wind-swept ground, at the foot of a north-facing slope.

Thanks to this, a plant that’s “half a zone too tender” can often still be grown by placing it in the warmest, most sheltered corner of the garden.

Limits of the method — what a USDA zone doesn’t tell you

The zone is a strong simplification and not a guarantee of survival. It accounts only for the lowest temperature, yet overwintering depends on many other factors:

• Snow cover — snow insulates roots and buds; the same plant overwinters more easily under snow than on bare, frozen ground.
• Wind — freezing wind desiccates the shoots of conifers and evergreens (winter desiccation), often more dangerous than frost itself.
• Moisture and drainage — many plants die in winter not from cold but from freezing in wet soil; lavender and juniper prefer a dry, free-draining substrate.
• Temperature swings — alternating thaws and frosts are often more harmful than a stable, hard winter; they de-harden the plant and damage the roots.

So treat the zone as a starting point, not a verdict. Combine it with knowledge of the site, soil and microclimate.

Next steps

You now know your zone and how to read the USDA indicator on plant cards. Take a look at the garden calendar to plan work in step with the season, and before the first frosts read our guide on getting the garden ready for winter — covering tender plants and mulching can shift their real hardiness by half a zone.