Last Frost Date Ottawa — When Is It Safe to Plant?
Ottawa's last frost is May 9 — first frost October 12, ~155-day season, Zone 5a. Full planting calendar with indoor start dates and outdoor transplant dates for 20+ vegetables.
Ottawa's last frost date is May 9 — the anchor date for your entire planting schedule. First fall frost arrives around October 12, giving Ottawa approximately 155 frost-free days in Zone 5a. Comfortably between the Prairie cities and Toronto, Ottawa's season is long enough for tomatoes, peppers, butternut squash, and even short-season sweet corn.
Ottawa's Ottawa Valley location brings its own climate quirks: cold, snowy winters, hot and humid summers, and springs that can be unpredictable. Getting the timing right — starting seeds indoors in February and March, watching for late May cold snaps, and taking advantage of a warm October — makes the difference between an average Ottawa garden and a great one. Use this guide alongside the seed starting calculator to build your full planting schedule.
Ottawa at a glance: Last frost May 9 · First frost October 12 · Growing season ~155 days · Hardiness zone 5a. Safe to transplant tomatoes and peppers after May 20–25. Keep frost cloth ready until June 1.
Last Frost Date Ottawa — Historical Average
The historical average last frost date for Ottawa is May 9, based on Environment and Climate Change Canada climate normals (1991–2020). The full historical range spans from April 25 (earliest recorded) to May 25 (latest), reflecting year-to-year variation.
Ottawa's hardiness zone is 5a — slightly colder than Toronto (6b) and matching Montreal's outer suburbs. The frost-free growing season averages 155 days from last spring frost (May 9) to first fall frost (October 12). This is shorter than Toronto's 197 days, which is why Ottawa gardeners need to time heat-loving crops carefully — start indoors early, transplant on schedule.
For frost-sensitive crops (tomatoes, peppers, basil, eggplant, squash), wait until May 20–25 to transplant — about 2 weeks past the average to absorb late-spring frost risk. For cool-season crops (peas, lettuce, spinach, kale, broccoli), sow as early as late April when soil reaches 4°C. Use the frost calculator for adjusted dates if you're outside the urban core (Kanata, Orléans, rural Ottawa Valley).
For a deeper dive on Ottawa's frost dates — suburb-by-suburb breakdown (Kanata, Barrhaven, Orléans, Stittsville, Gatineau, Hull), Leda clay soil's effect on safe planting dates, and how Ottawa compares to Montreal and other Canadian cities — see the dedicated Last Frost Date Ottawa-Gatineau page.
📅 Ottawa's Key Frost Dates
Ottawa Planting Calendar — Full Table
All dates calculated from Ottawa's average last frost of May 9. "Start indoors" counts backward by the recommended weeks. "Direct sow" is when it's safe to plant seeds in the garden.
| Vegetable | Start Indoors | Transplant Out | Direct Sow | Days to Harvest |
|---|---|---|---|---|
| 🍅 Tomatoes | Mar 14–28 | May 9–20 | — | 55–80 days |
| 🌶️ Peppers | Feb 27–Mar 13 | May 19–29 | — | 60–80 days |
| 🍆 Eggplant | Feb 27–Mar 13 | May 19–29 | — | 65–75 days |
| 🥒 Cucumbers | Apr 18–25 | May 16–23 | May 16–23 | 50–65 days |
| 🎃 Zucchini / Summer Squash | Apr 18–25 | May 16–23 | May 16–23 | 50–60 days |
| 🎃 Winter Squash / Butternut | Apr 11–18 | May 16–23 | May 16–23 | 85–100 days |
| 🌽 Sweet Corn | — | — | May 9–24 | 65–80 days |
| 🥦 Broccoli | Mar 21–Apr 4 | Apr 25–May 9 | — | 60–80 days |
| 🥬 Cabbage | Mar 14–28 | Apr 25–May 9 | — | 70–120 days |
| 🧅 Onions (from seed) | Feb 7–21 | Apr 25–May 9 | — | 100–120 days |
| 🧅 Onions (sets) | — | — | Apr 25–May 9 | 65–75 days |
| 🥕 Carrots | — | — | Apr 20–Jun 15 | 70–80 days |
| 🫘 Bush Beans | — | — | May 9–Jul 1 | 50–60 days |
| 🟢 Peas | — | — | Apr 10–May 1 | 55–70 days |
| 🥬 Lettuce | Mar 21–Apr 4 | Apr 20–May 9 | Apr 15–May 20, Aug 1–Sept 1 | 45–60 days |
| 🌿 Spinach | — | — | Apr 10–May 15, Aug 1–Sept 1 | 40–50 days |
| 🥦 Kale | Mar 21–Apr 4 | Apr 20–May 9 | Apr 20–May 15, Aug 1 | 55–75 days |
| 🌿 Basil | Apr 11–18 | May 19–29 | — | 60–90 days |
| 🫚 Garlic | — | — | Plant Oct 1–15 | Harvest Jul–Aug |
| 🥔 Potatoes | — | — | Apr 25–May 15 | 70–120 days |
| 🌸 Marigolds | Mar 28–Apr 11 | May 9–20 | May 9–20 | 50–60 days |
Get Your Personalized Ottawa Planting Schedule
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🌱 Free Seed Starting Calculator🍅 Growing Tomatoes in Ottawa
Ottawa's 155-day season supports tomato varieties up to about 78–80 days — significantly more flexibility than Prairie cities but slightly less than Toronto. You can grow most popular heirlooms, large slicers, paste tomatoes, and cherry types with confidence. Like Toronto, Ottawa's hot humid valley summers create blight and fungal disease pressure — disease-resistant varieties and good airflow matter.
Best Tomato Varieties for Ottawa
💡 Ottawa tip: Ottawa's Ottawa Valley location creates a humidity trap in summer — hot, moist air sits between the Gatineau Hills and the escarpment. This is ideal for fast tomato ripening but also accelerates blight. Remove lower leaves from tomato plants once they reach 60 cm tall, space plants 60–75 cm apart, and never water overhead.
Ottawa's Sweet Spot: What Zone 5a Gets Right
Ottawa's position at Zone 5a opens up crops that Prairie cities can't reliably grow, while its cooler climate compared to Toronto means better cool-season crops and less summer stress on leafy greens. Here's what Ottawa does especially well:
Winter Squash
Butternut, acorn, delicata, and spaghetti squash all fit comfortably in Ottawa's 155-day season. Start indoors mid-April, transplant mid-May, harvest in October.
Sweet Corn
Ottawa Valley is excellent corn country. Direct sow mid-May after soil warms and harvest in August. Both early (65-day) and mid-season (75-day) varieties work reliably.
Brassicas
Ottawa's cool springs and falls are ideal for broccoli, cabbage, Brussels sprouts, and cauliflower. Start in March for spring crops and again in June for fall harvests that run through October.
Heirloom Tomatoes
80-day varieties like Brandywine and Cherokee Purple are within Ottawa's reach — not feasible in Calgary or Winnipeg. Transplant by May 9–15 and they'll ripen well before the October 12 first frost.
Root Vegetables
Carrots, beets, parsnips, and turnips thrive in Ottawa's climate. Cool September and October nights build exceptional sweetness — especially in parsnips and carrots left in the ground until after the first light frosts.
Hardneck Garlic
Plant in early October, mulch with 10–15 cm of straw, and harvest the following July. Ottawa's cold winters produce excellent bulb development. This is one of the highest-value crops an Ottawa gardener can grow.
Ottawa-Specific Gardening Tips
Watch for late frosts in mid-May
May 9 is an average. Ottawa regularly sees cold nights into the third week of May — Environment Canada records show frost has occurred as late as May 24 in some years. Don't transplant frost-sensitive crops without checking the 14-day forecast first, and keep frost cloth ready until May 20.
Start onions in February — most Ottawa gardeners start too late
Onions from seed need 10–12 weeks indoors before transplanting. With a May 9 last frost, that means starting in early February. Most Ottawa gardeners wait until March, end up with small transplants, and wonder why their onions are disappointing. Set a February 7–21 calendar reminder and you'll have the best onions of your life by August.
Use Ottawa's long fall — October is productive
Ottawa's first frost averages October 12, which means September and the first two weeks of October are fully productive. Tomatoes, peppers, cucumbers, and beans continue yielding through September. Cold-tolerant crops — kale, spinach, arugula, chard — actually improve after light October frosts and can be harvested well into the month.
Ottawa's clay soil benefits from raised beds
Much of Ottawa — particularly Kanata, Barrhaven, and the western suburbs — sits on heavy Leda clay. This soil drains poorly, compacts easily, and stays cold well into spring. Raised beds are especially valuable here: they warm up 2–3 weeks earlier, drain freely, and let you fill with your choice of soil mix. Use the raised bed calculator to plan yours.
Succession sow beans every two weeks
Ottawa's long season makes succession sowing beans highly worthwhile. Sow your first batch May 9, then every two weeks through July 1. Each sowing gives you a 2-week harvest window, meaning you can have fresh beans from late June through early October. Three or four sowings fill a family's summer bean supply without a glut.
Month-by-Month Ottawa Garden Calendar
- Start onions and leeks indoors (early February)
- Start peppers and eggplant indoors (late February)
- Order seeds — popular varieties sell out by March
- Start tomatoes indoors (mid-March)
- Start broccoli, cabbage, kale (late March)
- Start lettuce for early transplant (late March)
- Direct sow peas outdoors under frost cloth (late March)
- Start cucumbers, squash, basil indoors (mid-April)
- Transplant cold-tolerant crops outdoors (broccoli, kale, lettuce, onions)
- Direct sow carrots, spinach, peas outdoors
- Harden off tomato seedlings
- Transplant tomatoes after May 9
- Direct sow beans and corn (mid-May)
- Transplant cucumbers, squash, basil (mid-May)
- Transplant peppers and eggplant (late May)
- Keep frost cloth ready until May 20
- Harvest peas, lettuce, early beans (June)
- Harvest tomatoes, cucumbers, zucchini (July onward)
- Succession sow beans every 2 weeks through July 1
- Sow fall lettuce, spinach, kale (early August)
- Continue harvesting tomatoes, peppers, cucumbers through September
- Harvest winter squash before October 12
- Harvest fall kale, spinach through frost
- Plant garlic (October 1–15)
- Clear beds and add compost layer
Frequently Asked Questions
What is the last frost date in Ottawa?
Ottawa's last frost date is May 9 (Zone 5a). For frost-sensitive crops like tomatoes and peppers, add a 1–2 week buffer and transplant outdoors around May 20–25. Always harden off transplants for 7–10 days before moving them outside.
When is the last frost in Ottawa?
Ottawa's average last spring frost is May 9. It can range from late April in warm years to late May in cold years. Keep frost cloth ready until May 20 and check Environment Canada's forecast before transplanting frost-sensitive crops.
When should I start tomatoes indoors in Ottawa?
Start tomato seeds indoors between March 14 and March 28 — 6 to 8 weeks before Ottawa's May 9 last frost. Ottawa's 155-day season supports varieties up to 80 days, including most heirlooms. Use the seed starting calculator for a full schedule by vegetable.
What hardiness zone is Ottawa?
Ottawa is Canadian Hardiness Zone 5a. This puts it between Toronto's Zone 6b and the Prairie cities at Zone 3–4. The Gatineau side of the river (Quebec) is sometimes listed as Zone 4b due to slightly colder temperatures.
Can I grow butternut squash in Ottawa?
Yes — butternut squash fits comfortably in Ottawa's 155-day season. Start indoors in mid-April, transplant mid-May, and harvest in late September to early October before the October 12 first frost. This is not reliably feasible in Prairie cities.
How does Ottawa compare to Toronto for gardening?
Toronto has about 42 more frost-free days than Ottawa (197 vs 155). Toronto can grow sweet potatoes, watermelons, and 90-day heirlooms that Ottawa can't reliably manage. Ottawa's cooler climate is actually better for cool-season crops — lettuce, spinach, and kale last longer in the garden before bolting compared to hot Toronto summers. See our lettuce planting guide for Ontario for spring and fall sowing windows by city.
Trees & Shrubs for Ottawa (Zone 5)
Ornamental shrubs and trees suited to Ottawa's Zone 5a climate — including the species that line Commissioners Park and thrive in the Capital's cold winters.
📖 Related Guides & Calculators
Plan your Ottawa garden from seed to harvest.