Ontario Seed Starting Schedule 2026
Published: April 24, 2026
Ontario indoor seed starting begins in late January with onions and leeks, ramps up through February (peppers, eggplant), peaks in March (tomatoes, brassicas, celery), and wraps up in April (cucumbers, squash, basil). The exact dates shift by 2–3 weeks between Toronto (earlier) and Ottawa (later) reflecting their different last-frost dates. This guide provides a month-by-month schedule for every Ontario city with equipment requirements, hardening off procedure, and the common mistakes that cause seed starting failures even with good intentions.
Ontario Seed Starting Calendar — Master Table
This master table shows Toronto and Ottawa indoor start dates for each common vegetable. Other Ontario cities fall between these two: Hamilton follows Toronto; London follows Toronto plus 1 week; Kitchener same as London; Kingston follows Ottawa; Windsor 1 week earlier than Toronto; Niagara 1–2 weeks earlier than Toronto; northern Ontario (Sudbury, Thunder Bay) 2–3 weeks later than Ottawa.
Dates are calculated by counting back from each city's last frost date: onions 10–14 weeks, peppers 8–10 weeks, tomatoes 6–8 weeks, brassicas 4–6 weeks, cucumbers and squash 2–4 weeks. Earlier starts produce rootbound stressed seedlings; later starts produce undersized transplants that take longer to establish. The middle of each window is the target.
| Crop | Toronto (Last Frost April 20) | Ottawa (Last Frost May 6) |
|---|---|---|
| Onions, Leeks, Shallots | January 20–February 3 | February 5–19 |
| Celery, Celeriac | February 10–24 | February 25–March 10 |
| Peppers, Eggplant | February 15–March 1 | March 3–17 |
| Tomatoes | March 1–15 | March 17–31 |
| Broccoli, Cauliflower | March 15–April 1 | April 1–15 |
| Cabbage, Kale, Brussels Sprouts | March 15–April 1 | April 1–15 |
| Lettuce, Greens (for transplant) | March 15 | April 1 |
| Basil | March 22–April 5 | April 8–22 |
| Cucumbers, Zucchini | April 15–22 | May 1–8 |
| Winter Squash, Melon | April 15–22 | May 1–8 |
| Direct-sow outdoors after frost | Carrots, beets, beans, corn | Same list, 2 weeks later |
January: The Overlooked Start Month
Ontario seed starting begins in late January with alliums (onions, leeks, shallots). These slow-growing crops need 10–14 weeks indoor time to reach transplant-ready size. Toronto gardeners sowing January 20–February 3 will transplant mid-April onions that bulb up through summer for harvest in August–September. Skip the January start and you'll need to buy onion sets instead (which work fine but limit variety choice).
January daylight in Toronto: 9–10 hours. Even on the brightest January days, windowsill growing is inadequate for healthy seedlings. Grow lights are mandatory for January-February seed starting. Running lights 14–16 hours daily compensates for the short natural photoperiod.
What else to do in January: inventory seeds from previous years, order any varieties needed for upcoming starts, clean and sanitize seed trays and pots from last season, set up and test grow light rigs before the March rush, plan garden layout on paper. A well-organized January sets up the productive February–April seed-starting months.
Why Ontario gardeners skip January starts: most home gardening literature focuses on tomato and pepper starts (February–March), giving the impression that January is too early. For onions and leeks specifically, January is correct timing. Leek varieties like American Flag and Giant Musselburgh are worth the January investment for their strong flavour and long winter storage.
February: Peppers, Eggplant, and Slow Growers
Peppers need 8–10 weeks indoors — Toronto starts February 15–March 1; Ottawa March 3–17. Heat mat strongly recommended for pepper germination (21–27°C soil required). Without a heat mat, February pepper starts often fail at germination because Ontario homes are too cool. See our /when-to-plant-peppers-ontario guide for detailed pepper seed-starting.
Eggplant: same timing as peppers. 8–10 weeks indoors. Similar challenges — cool germination temperatures in Ontario homes. Heat mat essential. Varieties for Ontario: Black Beauty (80 days) for Toronto/southern Ontario; Early Midnight (55 days hybrid) for Ottawa and short-season areas.
Celery and celeriac: 10–12 weeks indoors. Toronto starts February 10–24; Ottawa February 25–March 10. Celery requires 21°C for germination and is famously slow and finicky. Many gardeners skip celery from seed and buy transplants. Worth trying if you want specific heirloom varieties unavailable as transplants.
February growing conditions: 10–11 hours of natural daylight in Toronto, cloudy much of the month. Grow lights at 14–16 hours daily. Room temperatures of 18–22°C are fine for most seedlings if heat mat is used for germination. Begin hardening off any indoor-sown plants that will transplant in late April — brief periods on a sunny windowsill (not yet outdoors).
March: The Main Event — Tomatoes and Brassicas
Toronto gardeners start tomatoes March 1–15; Ottawa gardeners March 17–31. This is 6–8 weeks before transplant — the standard tomato indoor window. Tomato germination is reliable at 18–22°C ambient (heat mat helpful but not essential). See our /when-to-plant-tomatoes-ontario guide for complete tomato timing and variety selection.
Brassicas (broccoli, cauliflower, cabbage, kale, Brussels sprouts): 4–6 weeks indoors. Toronto starts March 15–April 1; Ottawa April 1–15. Brassicas germinate in 5–10 days at cooler 15–21°C, making them easier than heat-loving crops. Transplants go outdoors 2–3 weeks before last frost (they tolerate light frost once hardened off).
Lettuce and greens for transplant: Toronto starts March 15; Ottawa April 1. Optional — many gardeners direct-sow lettuce outdoors instead, saving indoor space. Direct-sow outdoors 2–3 weeks before last frost once soil is workable. Indoor-started lettuce transplants produce about 2 weeks earlier than direct-sown for those who want the earliest harvests.
March is the busiest indoor growing month in Ontario. Space becomes tight on grow light racks. Peppers started in February are ready to pot up from cells to 4-inch pots in early March, requiring double the previous space. Tomatoes sown in early March germinate and need lit growing space within 10 days. Plan grow-light rig capacity for peak March loads.
April: Cucumbers, Squash, and the Final Push
Cucumbers, zucchini, summer squash: 2–4 weeks indoors only — these grow fast and become rootbound quickly. Toronto starts April 15–22; Ottawa May 1–8. Direct sowing outdoors is equally effective and skips the indoor step entirely. Many Ontario gardeners start half from seed indoors (for early harvests) and direct-sow the other half (for continuous production).
Winter squash and melons: same timing as cucumbers and summer squash. 2–4 weeks indoors max. Transplant outdoors after last frost when soil is 15°C+. For winter squash, this is the last indoor-start crop of the season — after April, everything else goes direct to garden.
Annual herbs: basil goes in last (April) — Toronto April 1; Ottawa April 8–22. Basil is cold-sensitive and grows quickly; 4–5 weeks indoors is adequate. Other annual herbs (cilantro, dill) direct-sow outdoors after last frost.
Hardening off begins in April for earlier-started crops. Onions and leeks sown in January are ready for outdoor adjustment in mid-April. Brassicas sown in mid-March are ready for hardening by mid-April. Peppers and tomatoes begin hardening in late April to early May depending on transplant target date. See the hardening off section below.
Equipment Guide for Ontario Seed Starting
Grow lights: T5 fluorescent fixtures ($80–150 for a 4-tube fixture) or LED grow panels ($60–200). Both work well. LED panels use less electricity, last longer (20,000+ hours), and run cooler. T5 fluorescents are older technology but produce excellent light spectrum for seedlings. Whichever you choose, run lights 14–16 hours daily, positioned 5–10 cm above seedlings, raised as plants grow.
Heat mats: $25–80 depending on size and thermostat control. Essential for peppers and eggplant; helpful for tomatoes, basil, and cucumbers; unnecessary for most cool-season crops (brassicas, lettuce, onions). Budget option: basic un-thermostated heat mat ($25–35). Best option: thermostat-controlled mat ($60–80) that maintains precise 24–26°C soil temperature.
Seed starting mix: Pro-Mix, Jiffy Mix, Black Gold, or Miracle-Gro Seed Starting Mix. Do NOT use garden soil (contains pathogens, weed seeds, drains poorly in trays). Seed starting mix is sterile, finely textured, and drains well. A single 10L bag covers 100+ 4-inch pots.
Potting soil (for transplanting up): standard potting mix with fertilizer. Brands: Pro-Mix, FoxFarm Ocean Forest, Miracle-Gro Potting Mix. Use after seedlings have 2–3 true leaves when potting up from cells to 4-inch pots.
Trays and pots: 1020 seed trays (standard 25×50 cm flats), 72- or 50-cell inserts for germination, 4-inch pots for potting up, clear humidity domes for seed trays during germination. Bottom-watering from a reservoir tray prevents damping off and keeps seed-starting mix evenly moist.
Bottom watering: fill tray bottom with 1–2 cm water, let pots absorb upward, drain excess after 30 minutes. This keeps surface dry (preventing damping off fungal disease) while supplying even moisture. Top-down watering splashes soil and creates conditions for disease.
Hardening Off — Ontario's Most Skipped Step
Hardening off is 7–10 days of gradual outdoor exposure before final transplant. Indoor-grown seedlings have soft cuticles, large delicate leaves, and no adaptation to wind, UV, or temperature fluctuation. Moving them directly from indoor conditions to full-sun outdoor garden kills most of them within 3 days or damages all of them permanently.
Day 1–2: 1–2 hours in protected shade (north side of house, under a tree). Bring back indoors for remainder of day.
Day 3–4: 3–4 hours in dappled or partial sun. Still bringing back indoors overnight. Begin morning sun exposure.
Day 5–6: 5–6 hours outdoors including morning sun. If overnight temperatures above 10°C, leave outdoors overnight in sheltered location.
Day 7–10: full outdoor conditions including full sun. Plants should be outdoors 24/7 in their transplant location by day 7–10. Check overnight forecasts — bring indoors if frost threatens.
Cold snap exception: if forecast overnight lows fall below 8°C during hardening off, bring plants indoors overnight. Ontario's late-May cold snaps occasionally damage hardening-off plants even at this stage. Better to extend hardening off by a few extra days than lose plants to cold.
Ontario's most skipped step: many gardeners transplant directly from 21°C indoor growing conditions to the garden, producing transplant shock that stalls growth for 2–3 weeks. Hardening off is 7–10 days of modest effort that prevents this shock and sets plants up for immediate productive growth after transplant.
Frequently Asked Questions
When should I start seeds indoors in Ontario?
Depends on the crop. Onions and leeks: late January to early February. Peppers and eggplant: mid-February to early March. Tomatoes: early to mid March. Brassicas (broccoli, cabbage, kale): mid-March to early April. Cucumbers and squash: mid to late April. The general rule: count back 6–8 weeks from your city's last frost date for tomatoes; longer for slow-growing crops (peppers 8–10, onions 10–14); shorter for fast-growing crops (cucumbers 2–4).
Do I need grow lights to start seeds in Ontario?
Strongly recommended for any January–March starts. Ontario winter daylight is 9–11 hours with significant cloud cover, producing low total light that results in leggy weak seedlings even on south-facing windowsills. Grow lights running 14–16 hours daily produce compact sturdy transplants. T5 fluorescent fixtures or LED grow panels both work; budget $80–200 for a basic setup. April starts (cucumbers, squash) can succeed on sunny windowsills.
Can I start tomatoes indoors in February in Ontario?
Generally no — too early. February-started tomatoes become leggy, rootbound, and stressed by the time Ontario transplant dates arrive in mid-May. Toronto gardeners should start tomatoes March 1–15 (6–8 weeks before transplant). Exceptions: gardeners using greenhouses or polytunnels for early transplanting can start in mid-February. Standard outdoor gardens should wait for March.
What seeds can I start earliest in Ontario?
Onions and leeks are the earliest, starting January 20–February 5 in Toronto. These alliums need 10–14 weeks indoors to reach transplant size. Shallots follow the same schedule. Celery and celeriac start in mid-February (10–12 weeks indoors). Peppers and eggplant start mid-February to early March (8–10 weeks). Tomatoes start early to mid-March (6–8 weeks). Fast-growing cucumbers and squash start in April.
How long before last frost do I start seeds in Ontario?
Varies by crop. Onions: 10–14 weeks before last frost. Peppers, eggplant, celery: 8–10 weeks before. Tomatoes: 6–8 weeks before. Brassicas (broccoli, cabbage, kale): 4–6 weeks before. Lettuce and greens: 4–6 weeks before. Basil: 4 weeks before. Cucumbers, squash, melons: 2–4 weeks before. The general principle: slower-growing crops need more indoor time to reach transplant-ready size.
About the Author
Landscaping Expert & Writer · Raleigh, North Carolina · North Carolina State University
Jennifer Hall is a professional landscaper and lawn care writer based in Raleigh, North Carolina. She studied landscape horticulture at North Carolina State University, home to one of the country's leading turfgrass programs, and went on to build a specialized landscaping service serving the greater Raleigh-Durham region. Jennifer's expertise spans the Southeast and Mid-Atlantic transition zone, where she advises homeowners on warm-season grass selection, seasonal lawn care calendars, landscape design, and water-efficient gardening. Her writing brings together professional horticultural training and real-world experience in one of America's most challenging grass-growing climates.