Gardening glossary
Frost date
A frost date is a probability statistic, not a guarantee. It's the date by which there's typically a 50% chance the last (or first) freezing temperature of the season has occurred at your weather station. Some sources publish 10% and 90% probability dates as well — useful when you want to plant out conservatively or push the season.
There are two dates every gardener should know for their postcode:
- **Last spring frost** — the average date after which you're unlikely to see another freeze until autumn. This is when frost-tender annuals like tomatoes, peppers, basil, beans, and squash can safely go in the ground. - **First fall frost** — the average date of the season's first freeze, which ends the growing season for warm-weather crops.
Typical US averages by USDA zone:
- Zone 4: last frost late May, first frost mid-September (~120 frost-free days) - Zone 5: last frost around May 5, first frost early October (~150 frost-free days) - Zone 6: last frost mid-April, first frost mid-October (~180 frost-free days) - Zone 7: last frost early April, first frost early November (~210 frost-free days) - Zone 8: last frost mid-March, first frost mid-November (~240 frost-free days) - Zone 9+: largely frost-free year-round
In the UK, last-frost dates range from mid-April in the south coast and London to late May in upland Scotland. First-frost dates run from mid-October (Highlands) to late November (Cornwall, southwest).
Always treat the published date as a midpoint. If the 10% probability date is two weeks later, that's the safer planting target for valuable transplants. I also recommend checking the 10-day forecast — a single late frost can wipe out tomato seedlings even a week after your "average" last-frost date.