How to Grow Onions in Canada
How to grow onions in Canada starts with a question most guides skip: whether the crop fits your season at all. Onions need 100-120 days to maturity, so compare that against your frost-free days before anything else. Start indoors February-March to maximize bulb size before the summer solstice. Give them full sun and space them 8-10 cm (3-4 in) within row, 30-40 cm (12-16 in) between rows.
Do onions fit your Canadian season?
Subtract days to maturity from your frost-free days. If the answer is not comfortably positive, the crop will not finish — no amount of good technique fixes an arithmetic problem. Onions need around 120 days from sowing or transplanting.
| Season band | Frost-free days | Days to maturity | Does it fit? |
|---|---|---|---|
|
Long season Zones 7-9 |
150-222 frost-free days | 100-120 days to maturity | Comfortable fit — room for a slow start. |
|
Medium season Zones 4-6 |
130-170 frost-free days | 100-120 days to maturity | Fits, but with little margin. Choose a faster cultivar. |
|
Short season Zones 2-3 |
90-130 frost-free days | 100-120 days to maturity | Too long for the shortest seasons in this band — start indoors, use season extension, or pick a short-season cultivar. |
When to plant onions in Canada
Timing runs from your local last spring frost: roughly 28 March in Vancouver, around 20 April to 10 May in Toronto, 3 May in Montreal, 7 May in Edmonton and 23 May in Calgary. Start indoors February-March to maximize bulb size before the summer solstice.
Season extension for a short Canadian season
- Black plastic mulch laid two to three weeks before planting lifts soil temperature by several degrees — often the difference between a crop and a failure on the Prairies.
- Floating row cover adds roughly two to four weeks at each end of the season and keeps early pests off at the same time.
- Low tunnels and cold frames let hardy crops carry on well past the first frost, and let hardy sowings start earlier.
- Short-season cultivars are the cheapest form of season extension. Choosing one that matures two weeks earlier costs nothing and removes the risk entirely.
Soil and site
Well-drained soil, pH 6.0-7.0. Light feeder.
Watering
Even, consistent moisture through bulb formation; taper off as tops begin to fall over.
Spacing and layout
Space onions 8-10 cm (3-4 in) within row, 30-40 cm (12-16 in) between rows. Crowding is the most common cause of disappointing yields — plants compete for light and water, and poor airflow between them raises disease pressure sharply.
Companion planting
Carrots (VOC masking works both directions).
Common problems
Onion maggot. Day-length variety matters at Canadian latitudes — long-day varieties are the reliable choice nationwide.
Cold spring soil is behind more Canadian failures than any pest. Seed sown below its germination minimum rots rather than sprouts, and a warm-season transplant set out into cold ground is stunted for the rest of the season even if it survives. Waiting a week is almost always cheaper than re-sowing.
Turn growing onions into a written plan. The Canada Vegetable Garden Planner (printable PDF) has frost-date planning pages, bed layouts, crop rotation, a sowing log and a harvest tracker — 70 printable pages.
Frequently Asked Questions
Can I grow onions in Canada?
Onions need around 120 days, so compare that against your frost-free days — roughly 90-130 on the Prairies, 130-170 through Central Canada and the Maritimes, and 150-222 on the coast.
When should I plant onions in Canada?
Start indoors February-March to maximize bulb size before the summer solstice. Work from your local last frost — around 28 March in Vancouver, 20 April to 10 May in Toronto, 3 May in Montreal and 23 May in Calgary.
How far apart should onions be planted?
Space them 8-10 cm (3-4 in) within row, 30-40 cm (12-16 in) between rows.
What usually goes wrong with onions in Canada?
Onion maggot. Day-length variety matters at Canadian latitudes — long-day varieties are the reliable choice nationwide. Cold spring soil is the other common cause of failure — sowing before the soil has reached the crop's germination minimum causes seed to rot rather than sprout.
Last updated 25 August 2026
Tools That Help With This Crop
Use these links when the guide moves from reading into sowing, planting, watering, and keeping the crop healthy.
Plan the next step
Use the printable SoilCommander planner for your region to turn this guide into sowing dates, bed layouts and weekly garden tasks.