CANADA PLANTING GUIDE

Growing Onions in Canada — Long-Day Varieties, Sets vs Transplants & Storage

Why long-day varieties are the only ones that bulb in Canadian gardens, the three planting methods (sets, transplants, direct seed) and which to choose by region, curing for winter storage, and defending against onion maggot, neck rot, and downy mildew.

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Onions look easy and mostly are — but two upstream decisions determine whether you get a pantry full of storage onions or a tray of disappointing scallions: choosing a long-day variety, and picking the right planting method for your region. Get those right and a 4-foot row of transplants yields 100-150 onions that store 6-12 months at $0 a kilo.

What follows is onion growing for actual Canadian conditions: the long-day rule, sets vs transplants vs direct seed, planting and care, harvest signals, the 2-3 week cure, winter storage, and the 5 most common Canadian onion problems — led by onion maggot.

The Long-Day Rule — Why It Matters

Onions start forming bulbs when day length reaches a variety-specific threshold. Canada sits at 43°N to 70°N, so summer days are 14-16+ hours long — only long-day varieties bulb properly here.

⚠️ Why short-day onions fail in Canada. Short-day varieties trigger bulbing as soon as day length hits 10-12 hours — that happens in March in southern Canada, before any meaningful leaf growth. Every leaf that emerges before bulbing becomes one ring of the bulb. Short-day onions in Canada start bulbing with 2-3 leaves and produce scallion-sized bulbs or none at all. Always check the seed packet or catalogue label — American garden brands often stock all three types side-by-side. Canadian seed houses (Veseys, William Dam, West Coast Seeds) only stock long-day + day-neutral.

Sets vs Transplants vs Direct Seed

Best Canadian Onion Varieties

Planting Window by Canadian Region

Planting and Care

1. Bed prep: loose well-drained soil. Work in 5 cm of compost. Soil pH 6.0-6.8. See Composting in Canada.
2. Spacing: transplants and sets 10-15 cm apart for storage bulbs (wider = bigger bulbs); 5 cm for green onions. Rows 30 cm apart.
3. Planting depth: shallow! Plant transplants and sets so the top of the bulb sits at soil level — deeper and bulbs stay small. Direct seed 1 cm deep.
4. Row cover immediately — from day one until early July. Blocks onion maggot adults (the #1 Canadian onion pest) and increases spring soil temperature.
5. Water consistently: 2.5 cm/week, more in hot dry weather. Drip or soaker preferred. Stop watering when tops start to flop (2-3 weeks before harvest) — helps cure-readiness. See Watering in Canada.
6. Feeding: light side-dress of balanced organic fertilizer at 6 weeks. Stop feeding by mid-summer — late nitrogen produces lush tops at the expense of bulb formation and storage life.
7. Weed often, weed shallow — onions have shallow roots; deep cultivation damages them. Hand-pull within 5 cm of plants. Mulch lightly with straw after bed warms.

Onion Maggot — Canada's #1 Onion Pest

Delia antiqua — the onion root maggot — is the single biggest Canadian onion threat, especially in Ontario, Quebec, and the Maritimes. Three generations per summer can destroy a row. Defence is preventive only — once larvae are inside the bulb, nothing reaches them.

• Row cover from day of planting until early July — the most effective control. Adult flies cannot reach the plants to lay eggs.
• Crop rotation — never plant onions/garlic/leeks/shallots in the same bed two years running. Overwintering pupae emerge from previous Allium soil.
• Transplants beat sets and direct seed — healthier larger plants tolerate light damage better.
• Diatomaceous earth ringed around plants at planting deters egg-laying.
• Beneficial nematodes (Steinernema feltiae) applied to soil at planting in heavy-pressure areas.
• Avoid fresh composted manure near onions — the ammonia attracts adult flies.
• Onion + carrot interplant — the volatile oils confuse onion maggot and carrot rust fly. Less effective alone than row cover but stacks well.

Harvest, Cure, Store

Harvest signal

Tops have yellowed and 50%+ of the tops have flopped at the neck. Do NOT bend tops over manually — the old "bend tops" advice is wrong. Bending interrupts the natural curing process and shortens storage. Let them fall on their own. Wait for a dry day; harvest before fall rains — wet bulbs at harvest is the #1 cause of neck rot in storage.

Cure 2-3 weeks

Lay or hang harvested onions in a single layer in a dry well-ventilated shaded area at 20-30°C, 60-70% humidity. A garage, covered porch, shed, or attic works. Direct sun cooks the bulbs; damp basements grow mold. Use a fan to improve airflow indoors. Done when: outer skin paper-dry and tight, neck dry and shrunken, tops fully brown halfway down.

Trim and store 6-12 months

After curing, cut tops 2-3 cm above the bulb. Store at 0-4°C, 60-70% humidity, complete darkness. Mesh bags, paper bags, braided strings, ventilated crates — never plastic. Unheated basement, root cellar, attached garage in mild winters, or insulated shed. Check monthly — remove any soft, sprouted, or moldy bulbs (one bad onion ruins the bag). DO NOT store with potatoes (release moisture). Garlic and winter squash store well alongside.

Where to Buy Canadian Onion Seed, Sets, and Transplants

• Veseys Seeds (Charlottetown, PEI) — sets, seed, and transplant bundles. Ships nationally. The standard.
• Dixondale Farms (Texas, ships to Canada) — the largest onion-transplant supplier in North America. Order by January for spring delivery.
• William Dam Seeds (Dundas, ON) — broad seed selection.
• West Coast Seeds (Delta, BC) — BC + Coastal varieties.
• Eagle Creek Farms (Bowden, AB) — Prairie-adapted varieties.
• Solana Seeds (Quebec) — specialty + heirloom.

5 Most Common Canadian Onion Problems

Related Canadian Guides