Last Frost Date London Ontario — When Is It Safe to Plant?
London Ontario's last frost is April 22 — first frost October 18, ~178-day season, Zone 6a. Full planting calendar with indoor start dates and outdoor transplant dates for 20+ vegetables.
London Ontario's last frost date is April 22. First fall frost arrives around October 18, giving London approximately 178 frost-free days — a solid mid-range season for southwestern Ontario. London's position between Lake Erie to the south and Lake Huron to the west gives it a continental climate moderated by both lakes, with warmer temperatures than cities further inland.
That season length handles most standard varieties of tomatoes, peppers, cucumbers, squash, and melons without issue. Use this guide alongside the seed starting calculator to build your full planting schedule.
For a deeper dive on London's frost dates — the neighbourhood breakdown (Thames valley urban core, north and west London, rural Middlesex County, Port Stanley), the Great Lakes microclimate, comparison to Toronto, Windsor, and Hamilton, and frost protection — see the dedicated Last Frost Date London Ontario page.
London Ontario at a glance: Last frost April 22 · First frost October 18 · Growing season ~178 days · Hardiness zone 6a. Safe to transplant tomatoes, peppers, and cucumbers outdoors after May 5–10.
📅 London Ontario Key Frost Dates
London Ontario Planting Calendar — Full Table
All dates calculated from London Ontario's average last frost of April 22.
| Vegetable | Start Indoors | Transplant / Direct Sow | Fall Sow | Notes |
|---|---|---|---|---|
| 🍅 Tomatoes | Mar 1–15 | May 5–15 | — | Most 75–85 day varieties reliable |
| 🌶️ Peppers | Feb 15–Mar 1 | May 10–20 | — | SW Ontario summers = good pepper heat |
| 🍆 Eggplant | Feb 15–Mar 1 | May 15–25 | — | Reliable in a warm corner |
| 🥒 Cucumbers | Apr 1–15 | May 5–15 | — | Direct sow after May 10 works well |
| 🎃 Squash / Pumpkin | Apr 1–15 | May 5–15 | — | Large varieties feasible with 178-day season |
| 🍉 Watermelon | Apr 1–15 | May 15–25 | — | Short-season varieties (75 days) work |
| 🍠 Sweet Potatoes | Mar 15–Apr 1 (slips) | May 20–Jun 1 | — | Feasible — harvest before Oct 18 |
| 🌽 Sweet Corn | — | May 5–20 direct | — | Multiple successions possible |
| 🫘 Beans | — | May 5–Jul 1 direct | — | Succession sow every 2–3 weeks |
| 🥦 Broccoli | Mar 15–Apr 1 | Apr 20–May 10 | Jun 15–Jul 1 | Two crops per year |
| 🥬 Lettuce | Mar 1–Apr 1 | Apr 1–May 15 | Aug 1–Sept 1 | Shade cloth Jun–Aug |
| 🌿 Spinach / Peas | — | Mar 20–Apr 22 direct | Aug 1–15 | Direct sow early — frost tolerant |
| 🥕 Carrots | — | Apr 1–Jun 15 direct | — | Succession sow every 3 weeks |
| 🧄 Garlic | — | Oct 10–25 (fall plant) | — | Harvest July; hardneck varieties |
| 🧅 Onions | Jan 25–Feb 10 | Apr 20–May 5 | — | Long-day varieties for Ontario |
| 🌿 Basil | Apr 1–15 | May 15–25 | — | Cold-sensitive — wait for warm nights |
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🌱 Seed Starting CalculatorLondon Ontario's Climate — SW Ontario Growing Advantage
Between two Great Lakes
London sits roughly midway between Lake Erie to the south and Lake Huron to the west. Both lakes moderate the climate, reducing extreme cold in winter and buffering summer heat — though less dramatically than lakeside cities. The result is a reliable continental climate with earlier springs than inland Ontario cities at similar latitudes.
Thames River valley frost pockets and warm spots
The Thames River valley running through central London creates localized microclimates. Valley bottoms can collect cold air on still nights (frost pockets), while elevated spots above the valley and south-facing slopes are measurably warmer. Gardeners on higher ground often see 1–2 weeks more season than those in low-lying spots near the river.
What London grows well
London's Zone 6a and 178-day season handle the full range of common vegetables. Tomatoes, peppers, cucumbers, beans, squash, and melons are all reliable. Sweet potatoes are feasible in warm years. The strong agricultural region surrounding London (Elgin, Middlesex counties) means excellent access to transplants and local seeds suited to SW Ontario conditions.
How London Compares to Other Ontario Cities
| London | Toronto | Hamilton | Ottawa | |
|---|---|---|---|---|
| Zone | 6a | 6b | 6b/7a | 5a |
| Last frost | Apr 22 | Apr 20 | Apr 25 | May 9 |
| First frost | Oct 18 | Nov 1 | Oct 28 | Oct 12 |
| Season | ~178 days | ~197 days | ~186 days | ~155 days |
| Best for | Tomatoes, peppers, cucumbers, melons | Widest variety, longest season | Sweet potatoes, melons, long-season crops | All-round, garlic, root veg |
Frequently Asked Questions
What is the last frost date in London Ontario ?
London Ontario's last frost date is April 22 (Zone 6a). For frost-sensitive crops like tomatoes and peppers, transplant outdoors around May 5–10. Always harden off transplants for 7–10 days before moving them outside.
What hardiness zone is London Ontario?
London Ontario is Zone 6a — the same zone as Kitchener/Waterloo and slightly cooler than Hamilton (6b/7a) and Toronto (6b). Zone 6a supports all common vegetables and the majority of perennial flowers and shrubs suited to southern Ontario.
When should I start tomatoes indoors in London Ontario?
Start tomato seeds indoors between March 1 and March 15 — 6 to 8 weeks before London's April 22 last frost. Transplant outdoors around May 5–15 after hardening off. London's 178-day season supports most standard and mid-season tomato varieties up to about 80 days.
How long is the growing season in London Ontario?
London Ontario's growing season is approximately 178 frost-free days (April 22 to October 18). This is longer than Ottawa (155 days) and Kitchener (170 days), and comparable to Hamilton (186 days). The 178-day season reliably supports tomatoes, peppers, squash, melons, and most common vegetables.
📖 Related Guides & Calculators
Plan your London Ontario garden from seed to harvest.