Gardening glossary
Last frost
Last frost is the most-used date in the entire vegetable calendar. Almost every "when to plant" recommendation is expressed relative to it: "start tomato seeds 6 weeks before last frost," "transplant peppers 1–2 weeks after last frost," "direct-sow beans on last frost."
Typical US last-frost dates (50% probability) by zone:
- **Zone 3** (Anchorage, International Falls MN): late May to early June - **Zone 4** (Minneapolis, Burlington VT): mid-May - **Zone 5** (Chicago, Denver, Boston): around May 5 - **Zone 6** (Philadelphia, Kansas City, Seattle): mid- to late April - **Zone 7** (Washington DC, Raleigh): early April - **Zone 8** (Atlanta, Dallas, Portland OR): mid-March - **Zone 9+**: late February or earlier, often frost-free
Typical UK last-frost dates:
- **South coast and London**: mid-April - **Midlands and Wales**: late April - **Northern England**: early May - **Scotland (lowland)**: mid-May - **Scottish Highlands**: late May to early June
Two cautions I drum into Growli users:
1. **The published date is a 50/50 coin flip.** Half of years will see a frost after it. For high-value transplants, wait until the 10% probability date — typically 10–14 days later — or use frost protection (row cover, cloches) if you plant earlier. 2. **Soil temperature matters more than air temperature** for warm-season crops. Even after the last frost passes, tomato roots won't grow until soil hits ~60°F at 4 inches deep, and pepper roots want 65°F. In a cool spring, that can be 2–3 weeks after last-frost date.
Cool-season crops (peas, lettuce, spinach, brassicas, onions, potatoes) go in 4–8 weeks **before** last frost — they tolerate or even prefer the cold.