Gardening glossary
First frost
First frost is the closing bookend of the growing season. It's the average date — usually defined at 32°F (0°C) — when your location can expect its first overnight freeze of autumn. Crops that aren't frost-hardy need to be harvested or protected before it arrives.
Typical US first-frost dates (50% probability):
- **Zone 3**: late August to early September - **Zone 4**: mid-September - **Zone 5**: late September to early October - **Zone 6**: mid-October - **Zone 7**: late October to early November - **Zone 8**: mid-November - **Zone 9+**: late November or later, often frost-free
Typical UK first-frost dates:
- **Scottish Highlands**: mid- to late October - **Northern England and Scotland (lowland)**: late October - **Midlands**: early November - **Southeast England and London**: mid-November - **Cornwall and southwest**: late November
How to plan around it:
- **Count back days-to-maturity** for any direct-sown fall crop. Spinach at 45 days, sown 60 days before first frost (to give a 15-day shoulder), goes in mid- to late August in Zone 6. - **Garlic** is planted 3–6 weeks before first frost — late September to late October across most of the temperate range. Roots establish before the ground freezes; tops emerge in spring. - **Cover crops** like winter rye and crimson clover go in 4–8 weeks before first frost to establish enough biomass to overwinter. - **Tender crops** (tomatoes, peppers, basil, squash, beans) need to be harvested or protected. Row cover can buy 5–10°F of frost protection and 2–4 extra weeks.
The first frost is usually a light frost (28–32°F) followed by a stretch of mild weather — sometimes called an "Indian summer" in the US. A **killing frost** (below 28°F for several hours) ends the season definitively. Most years there's a 1–3 week gap between the two.