Starting seeds indoors is how Canadian gardeners beat a short season, you get a head start indoors while it is still frozen outside. The whole method comes down to one thing: counting back the right number of weeks from your last spring frost. Get that date right and everything else falls into place.
Step one: find your last frost date
Your last spring frost is the anchor for every indoor sowing date. It varies enormously across Canada, from March on the south coast of BC to well into June in the North. Look up your city's average last frost first, then count backward from it. You can find last frost dates for cities across Canada here.
Remember it is an average, not a guarantee. Keep the seedlings indoors until the danger of frost has actually passed for the year, and always check the forecast before moving anything out.
Step two: count back the weeks by crop
Different crops need different head starts. Here is the standard timing, measured in weeks before your last frost:
- Onions and leeks: 10 to 12 weeks before last frost (the earliest of the bunch).
- Peppers and eggplant: 8 to 10 weeks. They are slow and love warmth.
- Tomatoes: 6 to 8 weeks. Started too early they get leggy and root-bound.
- Broccoli, cabbage, cauliflower: 5 to 7 weeks.
- Basil and most herbs: 4 to 6 weeks.
- Cucumbers, squash, melons: just 2 to 3 weeks, and only if you start them indoors at all; they resent transplanting and often do better direct-sown after frost.
So if your last frost is around May 20, you would start onions in early March, peppers in mid-to-late March, and tomatoes in early April.
Step three: what direct-sows instead
Plenty of crops skip the indoor stage entirely, they go straight into the ground. Carrots, beets, radishes, peas, beans, lettuce, spinach, and corn are all better direct-sown. Cold-hardy ones (peas, spinach, lettuce) can go out a few weeks before last frost; warm ones (beans, corn) wait until after.
A few things that make or break seedlings
- Light, not a windowsill. A south window is rarely enough this far north; seedlings stretch and flop. A cheap shop light or LED a couple of inches above them makes all the difference.
- Warmth to germinate. Peppers and tomatoes want warm soil to sprout; a heat mat speeds things up.
- Do not start too early. The most common mistake is starting tomatoes in February and ending up with tangled, root-bound plants weeks before it is safe to plant out.
- Harden off before transplanting. Give seedlings a week of gradually increasing time outdoors before they move to the garden, or the sun and wind will shock them.
That is the entire system: find your last frost, count back the weeks for each crop, and start them under a light. Do it in the right order and you walk into spring with strong transplants ready to go the moment the weather turns.