Calendars
Growing calendars for northern zones
A growing calendar in Canada is built from two local numbers: your hardiness zone and your average last spring frost. Everything else — when to start basil indoors, when to move transplants out, when to direct sow carrots — counts backward or forward from those two anchors.
Two anchors: hardiness zone and frost date
Canada's plant hardiness zones run from 0 in the far north to 9 on parts of Vancouver Island, based on climate factors such as temperature, precipitation, and frost duration. The zone is most useful for deciding which perennial herbs and shrubs are likely to survive winter outdoors.
For annual sowing, the more important number is the average last spring frost for your municipality. That date marks roughly when it becomes safe to move tender transplants outside, and it is the point most seed-starting schedules count backward from.
Counting backward to start seeds indoors
Short Canadian seasons reward a head start. Many warm-season crops and several herbs are sown indoors weeks before the last frost so they are large enough to transplant once the soil warms. Typical indoor lead times include:
| Crop | Start indoors before last frost | Notes |
|---|---|---|
| Onions, leeks | 10–12 weeks | Slow to size up from seed. |
| Peppers, eggplant | 8–10 weeks | Need warm soil to germinate. |
| Tomatoes | 6–8 weeks | Avoid starting too early or seedlings get leggy. |
| Basil | 6–8 weeks | Sensitive to cold; transplant only after frost. |
| Parsley | 8–10 weeks | Germinates slowly. |
Light matters. Indoor seedlings generally need bright supplemental light for many hours a day to stay compact; a sunny windowsill alone is often not enough in late winter at northern latitudes.
What to direct sow instead
Not everything benefits from an indoor start. Root crops and several fast cool-season vegetables resent transplanting and are usually sown straight into the ground once conditions allow:
- Carrots, radishes, beets, and turnips — sow in place; they dislike root disturbance.
- Peas, beans, and spinach — germinate readily outdoors in cool soil.
- Cilantro and dill — bolt quickly, so successive small sowings outdoors work well.
A worked example
Suppose your average last frost is in mid-May. Counting backward, tomatoes would be started indoors around late March, peppers a couple of weeks earlier, and onions in early March. Hardy direct-sown crops like peas could go into the ground a few weeks before the frost date, while basil and other tender plants wait until nights stay reliably above freezing.
Extending a short season
Where the frost-free window is tight, common low-tech extensions include row covers, cold frames, and raised beds that warm earlier in spring. Choosing early-maturing varieties with low "days to maturity" figures also helps crops finish before the first autumn frost.