When to Start Seeds Indoors
Calculate the perfect time to start seeds indoors based on your last frost date. Get a complete planting schedule for 30+ vegetables.
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When to Start Seeds Indoors in Canada
Starting seeds indoors is how Canadian gardeners beat the short growing season. With cold winters and late spring frosts across most of the country, waiting to direct sow everything outdoors means your tomatoes won't ripen, your peppers will barely fruit, and your growing season will be cut short before many crops reach maturity. Starting seeds 6–12 weeks before your last frost date gives plants a head start that simply isn't possible any other way.
The key is working backward from your last frost date — the average date it's safe to transplant outdoors. Every vegetable has an ideal window: tomatoes need 6–8 weeks, peppers 8–10, onions 10–12. Start too early and you'll have leggy, root-bound seedlings. Start too late and you lose the advantage. This calculator takes the guesswork out.
Frequently Asked Questions
When should I start tomato seeds indoors in Canada?
Tomato seeds should be started indoors 6–8 weeks before your last frost date. For Toronto (last frost ~May 9), that means starting seeds around mid-March. For Calgary (last frost ~May 23), start around late March to early April. For Winnipeg (last frost ~May 25), start the first week of April. Use our calculator above to get your exact date.
What seeds should I start indoors vs direct sow?
Start indoors: tomatoes, peppers, eggplant, broccoli, cabbage, cauliflower, kale, onions, leeks, celery, and herbs like basil. Direct sow outdoors after frost: carrots, radishes, beets, peas, beans, corn, spinach, arugula, and turnips. These root vegetables don't transplant well and prefer to germinate in place.
Do I need a grow light to start seeds indoors in Canada?
Yes — for most of Canada, a grow light is almost essential. In February and March when you're starting seeds, winter light through windows is too weak and too short to produce healthy, stocky seedlings. A basic LED grow light ($30–$80) positioned 2–3 inches above seedlings for 14–16 hours a day makes an enormous difference. South-facing windows work in a pinch but usually produce leggy seedlings.
What is hardening off and why does it matter?
Hardening off is the process of gradually introducing indoor seedlings to outdoor conditions over 7–10 days before transplanting. Seedlings grown indoors are accustomed to stable temperatures, no wind, and artificial light. Moving them directly outside shocks the plant and can cause wilting, sunscald, or death. Start with 1–2 hours in a sheltered, shaded spot and increase time and sun exposure each day before leaving them out overnight.
What soil mix is best for starting seeds?
Use a dedicated seed-starting mix, not regular potting soil or garden soil. Seed-starting mixes are finer, lighter, and better-draining, which gives delicate seedling roots room to establish. Regular potting soil is too dense and retains too much moisture, inviting damping off — a fungal disease that kills seedlings at the soil line. Many Canadian gardeners make their own mix using equal parts peat moss (or coco coir), perlite, and vermiculite.
How do I know my last frost date in Canada?
Use our Frost Date Calculator to find your exact last frost date by city. Last frost dates for major Canadian cities: Vancouver ~April 15, Toronto ~May 9, Ottawa ~May 14, Calgary ~May 23, Winnipeg ~May 25, Regina ~May 27, Halifax ~May 6, St. John's ~May 25.
💡 Light Requirements
Seedlings need 12–16 hours of light daily. Use grow lights positioned 2–3 inches above seedlings. Rotate trays daily for even growth.
🌡️ Temperature
Most seeds germinate best at 18–24°C. Use a heat mat for faster germination. Once sprouted, slightly cooler temps (15–21°C) prevent legginess.
💧 Watering
Keep soil moist but not soggy. Water from below to prevent damping off disease. Mist delicate seedlings gently. Use room temperature water.
🌿 Hardening Off
Gradually expose seedlings to outdoor conditions 7–10 days before transplanting. Start with 1 hour in shade, increase daily. Bring in at night initially.
📚 Related Guides
Everything you need to go from seed to harvest.
🌱 Next: Get Your Crops in the Ground
The dates above assume the seed actually germinates on schedule, and that is where a cold Canadian house quietly costs you two weeks. Tomato seed wants 21–27 °C of soil and pepper seed 27–29 °C — warmer than almost any March windowsill. A heat mat under the tray fixes it; move it from the tomatoes to the peppers once the first flat is up, since they do not need it after germination.
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More Garden Planning Tools
📱 Free Embeddable Widget — Seed-Starting Countdown
Add our free seed-starting countdown to your garden club, blog, or community-garden site. It shows visitors exactly when to start each crop indoors for their own Canadian city (timed to that city's ECCC frost dates) and counts down live through the season. Copy the code below.
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Change city=Toronto to any Canadian city, or let visitors pick from the dropdown inside the widget. Free to use — please keep the GrowersGuide.ca credit link.