A hardiness zone tells you whether a perennial is likely to survive winter. It does not tell you when to plant lettuce. Annual vegetables are scheduled instead from two local dates: the average last spring frost and the average first fall frost. The zone is useful background, but the frost pair drives the calendar.

Tomato seedlings growing in a seedbed before transplanting
Warm-season seedlings are started indoors weeks ahead, then transplanted only after frost risk passes. Photo: Wikimedia Commons (CC BY-SA 4.0).

Step one: find your two dates

Look up your municipality's plant hardiness zone through Natural Resources Canada, then find your average frost dates by postal code with a tool such as the Old Farmer's Almanac planting calendar. The gap between the two frost dates is your frost-free window — the number of days warm-season crops have to grow outdoors.

Step two: separate cool-season from warm-season crops

The single most useful split in a Canadian garden is by temperature tolerance:

  • Cool-season crops — peas, radishes, lettuce, spinach, kale, broccoli, carrots, beets. These germinate in cold soil and tolerate light frost, so they can be sown around or slightly before the last frost.
  • Warm-season crops — tomatoes, peppers, cucumbers, beans, zucchini, squash. These are damaged by frost and sulk in cold soil, so they wait until after the last frost and until soil has warmed to roughly 10–15 °C.

Soil temperature is a better signal than the calendar. Air can feel warm while the soil stays cold; a simple soil thermometer at planting depth removes the guesswork for beans, cucumbers, and squash.

Step three: count backward for indoor starts

Long-season crops are started indoors and counted back from the last frost. A common pattern:

Last frost = anchor date Tomatoes start indoors 6-8 weeks before last frost Peppers start indoors 8-10 weeks before last frost Broccoli/cabbage start indoors 5-6 weeks before last frost Lettuce start indoors 4 weeks (or direct sow)

For example, with a last frost near May 25 on the prairies, tomatoes started indoors in the first half of April are the right size to transplant in early June, once the cold-snap risk has passed.

Worked example: a short prairie season

Saskatoon and Winnipeg both average their last frost around May 25, with a first fall frost in mid-to-late September — roughly 110–120 frost-free days. That is enough for short-season tomatoes, bush beans, cucumbers, and the full range of cool-season and root crops, but not for long-season pumpkins or melons. Cool-season crops go in through May; tender transplants wait until early June with frost cloth kept on hand.

Worked example: a longer southern-Ontario season

Toronto averages its last frost near April 20 and first fall frost near the end of October — close to 190 frost-free days. That longer window allows succession sowing (a second round of fast crops like lettuce and radishes), warm-season crops direct-sown by late May, and time for long-maturity varieties that would not finish further north.

Step four: stagger and extend

Two habits stretch a Canadian season at both ends:

  1. Succession sowing. Sow small batches of fast crops every two to three weeks instead of all at once, so the harvest arrives in a steady stream rather than a glut.
  2. Season extension. Row covers, cold frames, and cloches buy days in spring and fall, which matters most where the frost-free window is short.

Keep your own dated notes each year. Local microclimate — a south-facing wall, a valley, proximity to a large lake — can shift effective timing by a week or more from the published averages.

Continue: raised beds and watering basics · harvest timing by zone.