When to Plant Onions in Canada 2026 | Zone-by-Zone Guide

Onions are a kitchen staple, but in Canada they demand precise timing. Miss the planting window and you'll harvest marble-sized bulbs instead of the big, storage-worthy onions you were counting on. This guide gives you exact indoor start dates, transplant timing, and variety recommendations for Canadian zones 3 through 7.

Why Timing Is Everything for Canadian Onions

Onion bulb formation is triggered by day length, not temperature. When days reach a critical threshold, the plant shifts energy from leaves to bulb. The more leaf mass the plant has built before that trigger, the bigger the bulb you harvest.

In Canada, that day-length trigger arrives in mid-June. Plants transplanted in late May or June have almost no time to build leaf mass before bulbing begins — the result is small, disappointing onions.

The rule: Get onions in the ground as early as possible in spring. In zones 5 and 6, that means transplants in the soil by late April to mid-May.

Long-Day vs. Short-Day Onions — What Canadians Need

All Canadian gardeners (zones 3–8) should grow long-day onions, which require 14–16 hours of daylight to bulb. These are bred for the long summer days of northern latitudes.

Short-day onions (common in US Southern states) won't form proper bulbs in Canada — avoid them unless growing for greens only.

Recommended long-day varieties for Canada:

• Copra — excellent storage, reliable in zones 4–6
• Sturon — disease-resistant, great for zone 5 Ontario
• Patterson — top storage variety, stores up to 12 months
• Red Baron — flavourful red onion for zones 5–7
• Candy — intermediate-day type that works well in zone 6 transition areas

When to Start Onions Indoors — By Zone

Starting from seed gives you the widest variety selection and the best head start. Onion seedlings need 10–12 weeks indoors before transplanting.

Tip for zone 3–4 gardeners: If you missed the seed-starting window, purchase onion transplants or sets from a local nursery in April. Sets are less reliable for storage onions but are a good backup.

When to Transplant Onions Outside

Onions are cold-hardy and can handle light frosts down to about -4°C. You don't need to wait for your last frost date — you need the soil workable and daytime temps consistently above 7°C.

• Zone 3 (Edmonton, Winnipeg): Transplant mid-May, after the May long weekend
• Zone 4 (Calgary, Saskatoon): Transplant early May — soil workable, light frosts still possible but onions handle them
• Zone 5 (Ottawa, Toronto, Montreal): Transplant late April to early May
• Zone 6 (Niagara, Windsor): Transplant mid to late April — the earlier the better
• Zone 8 (Vancouver, Victoria): Transplant late March to early April

Growing Onions from Sets

Onion sets (small dormant bulbs) are the easiest starting point for backyard gardeners. Plant sets pointed-end up, 2–3 cm deep, 10–15 cm apart in rows 30 cm apart.

Sets can go in the ground 2–3 weeks before your last frost date and tolerate late cold snaps well.

The trade-off: Sets give you less variety choice and are prone to bolting if they're too large. Look for sets smaller than a dime — these are least likely to bolt prematurely.

Soil Prep and Spacing

Onions need well-drained, loose soil. Heavy clay restricts bulb expansion — amend with compost before planting.

• pH: 6.0–7.0
• Spacing: 10–15 cm between bulbs (closer = smaller bulbs, good for green onions)
• Depth: 2–3 cm for sets; just covering the roots for transplants
• Fertilizer: Balanced fertilizer at planting, then a nitrogen-rich side-dressing when plants are 15 cm tall

Stop fertilizing once bulbs begin to form — you'll see the neck of the plant swell slightly as a signal.

When to Harvest

Onions are ready when about half the tops have fallen over naturally. Push the remaining tops over and let the bulbs cure in dry weather for a few more days, then lift and cure in a warm, ventilated spot for 2–3 weeks before putting them into storage.

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Use the free planting date calculator at mygardenplanner.ca to get personalized indoor start and transplant dates for onions and 28+ other crops based on your zone and last frost date. The season planner lets you map your full crop schedule so nothing gets planted too late again.