When to Plant Sweet Corn in Ontario
Published: April 24, 2026 · Updated: April 27, 2026
Direct sow after last frost when soil reaches 60°F. Plant in blocks of at least 4 rows for wind pollination. Succession plant every 2 weeks for continuous harvest.
Sweet Corn grow well in this province with appropriate variety selection and standard Canadian planting timing.
Sweet Corn Planting Window for Ontario
Direct sow outdoors: April 27–May 7
Minimum soil temperature: 16°C (60°F)
Days to harvest: 65–90 days
Sun requirement: Full sun (8+ hours)
⚠ Direct sow corn after last frost when soil reaches 60°F. Plant in blocks of at least 4 rows for pollination. Succession plant every 2 weeks for continuous harvest.
Ontario Cities — Sweet Corn Planting Dates
City-specific frost dates and sweet corn planting windows for Ontario.
Growing Sweet Corn in Ontario
- Plant in blocks of at least 4 rows × 4 plants, not single rows — corn is wind-pollinated and single rows produce deformed ears.
- Sow successively every 2 weeks until 90 days before first fall frost for continuous harvest through summer.
- Side-dress with nitrogen when plants are knee-high and again at tasseling — corn is an extremely heavy feeder.
- Test for ripeness by puncturing a kernel: clear liquid is under-ripe, milky liquid is perfect, pasty is over-ripe.
Companion Planting for Sweet Corn
In Ontario gardens, pair sweet corn with Bush Bean, Pumpkin, Squash, Cucumber. Avoid planting near Tomato, Celery, which compete with or inhibit sweet corn growth.
Common Pests and Problems
Sweet Corn in Ontario are commonly affected by Corn Earworm, Cutworm, Corn Rootworm, Raccoons. Floating row covers installed at planting block most adult pests from laying eggs, and a weekly scouting routine catches infestations before they damage the crop.
Frequently Asked Questions
When should I plant sweet corn in Ontario?
In Ontario (Canadian Zones 5b–6b), direct sow sweet corn around April 27. Sweet Corn grow well in this province with appropriate variety selection and standard Canadian planting timing.
What is the best sweet corn variety for Ontario?
Ontario gardeners should prioritise varieties bred for shorter seasons or Canadian climates. For sweet corn in Canadian Zones 5b–6b, look for cultivars labelled under 90 days to maturity. Local nurseries and provincial seed exchanges curate varieties that ripen within Canadian frost-free windows.
How does Ontario's climate affect sweet corn?
Ontario spans Canadian Zones 5b–6b with frost-free seasons ranging from roughly 153 to 195 days. Sweet Corn need warm soil (16°C minimum) and steady heat, so timing transplants correctly is critical — too early and plants sit in cold soil; too late and frost cuts the season short.
Can I grow sweet corn in containers in Ontario?
Yes. Container growing on balconies and patios extends the viable growing area across every Canadian province. Dark-coloured containers warm up faster in spring and extend the season on both ends. Choose a 5-gallon or larger pot for sweet corn and water daily during hot summer weather, since containers dry out quickly.
When is the first fall frost in Ontario?
First fall frost dates in Ontario range from October 15 in the coldest areas to November 1 in the warmest. Most sweet corn plantings in Ontario are spring-timed to harvest before the first fall frost rather than as a second fall crop.