Growing Sweet Corn in Canada — Sow Dates & Sugar Genetics
Direct sow at 15°C soil. Block-plant (not rows) for full pollination. Pick the right sugar-gene variety (su / se / sh2) for your season and storage needs. Sow dates by city, succession schedule, raccoon defence.
Sweet corn is one of the most reliable Canadian summer crops if you plant a real block (not a row) and pick a variety that finishes inside your frost-free window. It's also one of the most frustrating crops if you don't — rows of poorly-pollinated cobs with scattered missing kernels are the most common backyard-corn failure across Canada. The fix is simple: 16+ plants in a block (4×4 minimum), the right sugar-gene type for your needs, and warm-enough soil at sowing.
Three decisions matter most. Soil temperature at sowing (15°C for normal sugary, 18°C for supersweet sh2). Variety days-to-maturity (60-day Polar Vee for Prairies, 94-day Silver Queen for southern Ontario). Block planting — corn is wind-pollinated and a single row will not produce full ears no matter how many plants are in it.
Sweet corn in Canada at a glance: Direct sow only after last frost when soil reaches 15°C (18°C for supersweet sh2). Coastal BC: late May. Toronto/Windsor: May 25–June 5. Ottawa/Montreal: June 1–10. Calgary/Edmonton/Winnipeg: June 5–15. Halifax: late May–early June. Plant in a block (4×4 minimum, 5×5 better), not a row — corn is wind-pollinated and rows produce ears with missing kernels. Match variety to season: 60–70 days for Prairies (Polar Vee, Early Sunglow), 75–85 days for Ontario/Quebec (Peaches & Cream), 90+ for coastal BC (Silver Queen). Harvest 17–24 days after silks first appear, when silks brown and a punctured kernel runs milky.
When should you plant sweet corn where you garden?
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Sweet Corn Sow Dates by Canadian City
Sweet corn needs warm soil more than most cool-season crops — the practical sow date is 1–2 weeks after last frost when soil temperature has reached 15°C at 5 cm depth. Supersweet sh2 varieties need warmer soil (18°C) and weaker seedling vigour, so push their sow dates back another week. The max-maturity column shows the longest variety that reliably finishes before first fall frost in each region.
| Region (City) | Zone | Last Frost | Sow Window | Max Days |
|---|---|---|---|---|
| Coastal BC (Vancouver) | 8a | Mar 15 | May 20–Jun 1 | 95 days |
| Vancouver Island (Victoria) | 8b | Mar 10 | May 15–Jun 1 | 95 days |
| BC Interior (Kelowna) | 6b | May 5 | May 25–Jun 5 | 90 days |
| Windsor (S. Ontario) | 7a | Apr 20 | May 20–Jun 1 | 100 days |
| Toronto / GTA | 6b | Apr 20 | May 25–Jun 5 | 95 days |
| Hamilton, Niagara | 6b/7a | Apr 25 | May 25–Jun 5 | 95 days |
| Ottawa | 5b | May 9 | Jun 1–10 | 85 days |
| Montreal | 5b | May 9 | Jun 1–10 | 85 days |
| Quebec City | 4b | May 17 | Jun 5–15 | 75 days |
| Calgary | 3b/4a | May 23 | Jun 5–15 | 68 days |
| Edmonton | 4a | May 14 | Jun 1–10 | 75 days |
| Saskatoon, Regina | 3b | May 21–25 | Jun 5–15 | 70 days |
| Winnipeg | 3b/4a | May 25 | Jun 5–15 | 75 days |
| Halifax | 6a | May 10 | May 25–Jun 5 | 90 days |
Sugar Genetics: su vs se vs sh2
Modern sweet corn comes in three sugar-gene types that determine sweetness, storage life, and seedling cold tolerance. Choosing the wrong type for your soil temperature or planting plan is the most common reason a packet of seeds disappoints.
| Type | Sweetness | Storage | Sowing soil | Examples |
|---|---|---|---|---|
| su (normal sugary) | Traditional | Hours (eat same day) | 10°C OK | Polar Vee, Golden Bantam, Early Sunglow |
| se (sugary enhanced) | Sweet | 2–4 days | 13°C+ | Peaches & Cream, Kandy Korn, Bodacious |
| sh2 (supersweet) | Very sweet (2–3× su) | 1+ week | 18°C+ | Honey Select, Mirai, Xtra-Tender |
Critical isolation rule: sh2 (supersweet) cross-pollinated by su or se produces tough, starchy kernels. If you grow more than one type, separate them by at least 8 metres OR stagger sowing dates by 14+ days so they don't tassel at the same time. Most home gardens are better off picking a single sugar-gene type and sticking with it across all blocks.
Block Planting: Why Rows Don't Work
Corn is wind-pollinated. Each ear holds 500+ kernels, and each kernel only develops if a pollen grain from the tassel (top of the plant) lands on its silk (one silk per kernel). A single long row of corn lets pollen blow off the side — most silks never get pollinated, and you get cobs with scattered missing kernels (sometimes called "gappy ears").
The minimum effective planting is 4 short rows of 4 plants — a 4×4 block (16 plants). For full-size ears across the whole block, 5×5 or 6×6 is better. Spacing:
- 30 cm between plants in the row
- 45 cm between rows
- Block dimensions: a 4×4 block fits in 1.4 m × 1.4 m (about 2 m²)
- For very small gardens (1–3 m²), hand-pollinate by bending tassels and tapping pollen onto silks at mid-morning peak shedding, or skip corn and grow something more space-efficient
Plant 2 seeds per hole at 2–3 cm depth (corn seeds are large and need to be buried), then thin to one seedling per hole once true leaves develop. Keep soil moist until germination — 7–14 days at 15°C, faster in warmer soil.
Sources: corn wind pollination — common gardening practice; consistent with this site’s growing-sweet-corn guide.
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Continuous Harvest: Succession Planting vs. Variety Stagger
One block of corn matures within a 7–10 day window, then it's done. Two methods extend the harvest:
- Succession planting: sow a new block every 14 days from your first safe sow date through July 1 (June 15 on the Prairies). Each block matures 14 days after the previous one — 6–8 weeks of fresh corn from 3–4 plantings. Best for medium-to-large gardens.
- Variety stagger: sow a short-season, mid-season, and long-season variety on the same day. June 1 sowing of Early Sunglow (62 days), Peaches & Cream (83 days), and Silver Queen (94 days) harvests August 2, August 23, and September 3 — a month of harvest from one planting day. Best for small gardens (one prep day).
Variety stagger is space-efficient but limits each variety to a single small plot (raising the gappy-ears risk). Succession planting allows full block size for each sowing. Most Canadian gardens with 5+ m² of corn space use succession; smaller plots use variety stagger.
Pests: Raccoons, Earworms, and Birds
Raccoons (the #1 destructive pest)
A family of raccoons can wipe out a 50-plant patch overnight when corn is at peak ripeness. The classic disaster: ears are 1–2 days from harvest, you walk out in the morning, and the whole block is shredded with raccoon prints around the base. Defences in descending effectiveness: electric fence (single strand at 15 cm and 30 cm above ground, runs the perimeter of the corn block), motion-activated sprinklers, harvesting at first ripeness (don't leave a single mature ear overnight), fencing tomato cages around individual maturing ears. Repellents (predator urine, hair clippings) rarely work for long.
Corn earworm (Helicoverpa zea)
Brown-and-grey caterpillars that feed on the developing kernels at the silk end of the ear. Visible as 2–3 cm grubs when you peel back the husk; damage is the top 3–5 cm of kernels (which can be cut off and the rest eaten). Control: spray BT (Bacillus thuringiensis kurstaki) on silks every 5 days from silk emergence through harvest, OR apply 4–5 drops of mineral oil directly into the tip of the silks 12–15 days after silking — this suffocates emerging caterpillars without affecting pollination (which is complete by then).
Birds and European corn borer
Sparrows and crows pull up newly-germinated seedlings to eat the kernel. Cover sowings with floating row cover until corn is 15 cm tall. European corn borer (white caterpillars in stalks and ears, mainly Ontario and Quebec) is controlled by the same BT treatment as earworms.
Harvest: The Milk Test
Sweet corn is ready 17–24 days after silks first emerge from the husk. Three signs together confirm ripeness:
- Silks are brown and dry. Bright green silks = too early.
- The ear feels full and firm when you squeeze gently through the husk.
- The milk test: peel back a small section of husk near the top, puncture one kernel with a thumbnail. Clear liquid = too early. Milky white liquid = ready. Doughy/no liquid = past prime (still edible but starchy).
Harvest in the early morning when sugars are highest. Snap the ear downward from the stalk with a sharp twist. Eat within hours (su varieties) or refrigerate immediately. For freezing, blanch ears 4 minutes in boiling water, cool in ice water, cut kernels off the cob, and freeze in single-layer trays before bagging. A late-season glut is classic relish material — our sister site has the tested recipe: HarvestGuide.ca — how to make corn relish →
📍 Related Canadian Garden Resources
Plan Your Sweet Corn Block
Use the frost calculator for your exact postal code, then add 1–2 weeks for soil warming. The harvest calculator confirms whether your chosen variety finishes before first fall frost.
Frequently Asked Questions
When should I plant sweet corn in Canada?
Direct sow sweet corn after last frost when soil reaches 15°C (10°C absolute minimum for su varieties; 18°C for sh2 supersweet). Coastal BC (Vancouver, Victoria): late May. Southern Ontario (Toronto, Windsor, Hamilton): May 25–June 5. Eastern Ontario and Quebec (Ottawa, Montreal): June 1–10. Prairies (Calgary, Edmonton, Winnipeg, Saskatoon): June 5–15. Halifax: late May–early June. Sweet corn needs warm soil; sowing into cold wet soil rots seeds before they sprout (especially the supersweet sh2 varieties, which have weaker seedling vigour). Always direct sow — corn is a grass with sensitive roots that resent transplanting.
What sweet corn varieties grow best in Canada?
Match days-to-maturity to your growing season. Short-season Prairies (60–70 days): Polar Vee (55 days, white), Early Sunglow (62 days, yellow), Trinity (68 days, bicolour) — choose Polar Vee for Calgary, Edmonton, Winnipeg, Saskatoon. Southern Ontario/Quebec (75–85 days): Peaches & Cream (83 days, the Canadian classic bicolour), Kandy Korn (89 days, yellow se), Honey Select (78 days, supersweet sh2). Coastal BC and Niagara (90+ days): Silver Queen (94 days, classic white), Mirai 350 (78 days, premium sh2). Best storage and longest-holding sweetness: supersweet sh2 varieties — Honey Select, Mirai, Xtra-Tender. For roadside-stand traditional flavour: normal sugary su varieties like Golden Bantam (78 days).
What's the difference between su, se, and sh2 sweet corn?
Sugar-gene types determine sweetness and storage life. Normal sugary (su): traditional sweet corn flavour, sugars convert to starch within hours of picking — eat the same day. Hardiest seedlings, most reliable germination in cool soil. Examples: Golden Bantam, Polar Vee. Sugary enhanced (se): sweeter than su, holds sweetness 2–4 days after harvest. Tender pericarp, good cool-soil tolerance. Examples: Peaches & Cream, Kandy Korn, Bodacious. Supersweet (sh2): 2–3× the sugar of su, holds 1+ week after harvest, dominant in commercial production. Needs warmer soil (18°C+) for germination — risky for cool Prairie springs. Isolation matters: sh2 cross-pollinated by su or se varieties produces starchy, tough kernels — keep sh2 at least 8 metres or 14 days apart in planting from other types. Examples: Honey Select, Mirai, Xtra-Tender.
Why does sweet corn need block planting instead of rows?
Corn is wind-pollinated. Each ear contains 500+ kernels, and each kernel develops only if a pollen grain from the tassel (top of plant) lands on a silk (one per kernel). Wind carries pollen in all directions — but if you plant a single long row, pollen blows off the edge and most silks never get pollinated, producing ears with scattered missing kernels. The minimum effective planting is a 4×4 block (16 plants). For full-size ears, use 5×5 or 6×6 blocks. Plant in 4 short rows with 30 cm between plants and 45 cm between rows. Hand-pollinate small plantings by bending tassels and tapping pollen onto silks at peak shedding (mid-morning). Single rows are the #1 cause of poorly-filled ears in Canadian home gardens.
How do I get continuous sweet corn harvest through the season?
Two methods. Succession planting: sow a new block every 14 days from your first safe sow date through about July 1 in southern Canada (June 15 in the Prairies). Each block matures roughly 14 days after the previous one, giving you 6–8 weeks of fresh corn. Variety stagger: sow short-season, mid-season, and long-season varieties on the same day. A June 1 sowing of Early Sunglow (62 days), Peaches & Cream (68 days), and Silver Queen (94 days) harvests August 2, August 23, and September 3 respectively — a month of continuous harvest from one planting day. Variety stagger is easier for small gardens (one planting day) but limits each variety to a 1-block plot. Succession planting allows more total volume but requires multiple plantings.
What pests damage sweet corn in Canadian gardens?
Three main pests across all of Canada. Corn earworm: caterpillars feed on the developing kernels at the silk end of the ear. Spray BT (Bacillus thuringiensis) on silks every 5 days from silk emergence through harvest, OR apply 4–5 drops of mineral oil directly into the tip of the ear silks after pollination is complete (12–15 days after silking) — this suffocates emerging caterpillars. Raccoons: the single most destructive pest in southern Canada — can wipe out a 50-plant patch overnight when corn is at peak ripeness. Defences: electric fence (most reliable), motion-activated sprinklers, harvesting at first ripeness (don't leave a single mature ear overnight), or fencing tomato cages around individual ears. Birds (sparrows, crows): damage seedlings; cover germinating plots with floating row cover until corn is 15 cm tall. European corn borer is regional (mostly Ontario/Quebec) — BT treats it effectively.
When is sweet corn ready to harvest?
Sweet corn is ready 17–24 days after silk emergence (when silks first appear at the top of each ear). Three confirmation tests: (1) silks have turned brown and dry; (2) the ear feels firm and full to the touch — squeeze gently from the husk side; (3) puncture a kernel with your thumbnail — the liquid that runs out should be milky white, not clear (clear = too early, doughy = too late). Harvest in the morning when sugars are highest, then either eat within hours (su, se varieties) or refrigerate immediately. Sugars convert to starch quickly: a 24-hour delay can drop sweetness by 25% in su varieties, less in se and sh2. The cliché 'put the pot on before you pick the corn' is real and based on the rapid sugar-to-starch conversion in normal sugary varieties.
How much sweet corn should I plant?
A single ear per stalk for most varieties (some early types produce 2 ears). For a family of 4 eating corn 2–3 times per week through August, plant a 4×6 block (24 plants = ~24 ears per planting) and succession-plant 2 more blocks 2 weeks apart for 72 ears over 6 weeks. For freezing or canning, calculate 12–15 ears per litre of frozen kernels — a 6-litre annual supply needs 80–100 ears (4 blocks of 25). Space requirements: each plant needs about 0.15 m² (30 cm between plants, 45 cm between rows), so a 24-plant block fits in 3.6 m². The 'one plant per square foot' Three Sisters guideline works for traditional plantings with beans and squash interplanted, but yields are lower per plant than dedicated corn blocks.