When to Plant Basil in Ontario
Published: April 24, 2026 · Updated: April 27, 2026
The classic companion to tomatoes in both the garden and the kitchen. Basil is a heat-loving herb that thrives in summer but is killed by even a brief cold snap below 50°F.
Basil grow well in this province with appropriate variety selection and standard Canadian planting timing.
Basil Planting Window for Ontario
Start seeds indoors: March 9–16 (varies by city — earliest in southern Ontario, latest on the Prairies)
Transplant outdoors: May 4–14 (after last frost in your city)
Direct sow outdoors: May 4–14
Minimum soil temperature: 16°C (60°F)
Days to harvest: 30–60 days
Sun requirement: Full sun (6+ hours)
Ontario Cities — Basil Planting Dates
City-specific frost dates and basil planting windows for Ontario.
Growing Basil in Ontario
- Never expose basil to temperatures below 50°F — even briefly — it turns black and dies.
- Pinch flower buds immediately as they appear to keep leaves large and productive.
- Harvest by cutting whole stems from the top, leaving lower sets of leaves to branch out.
- Plant next to tomatoes — basil is proven to repel whiteflies, aphids, and spider mites from tomato plants.
Companion Planting for Basil
In Ontario gardens, pair basil with Tomato, Pepper, Marigold, Oregano. Avoid planting near Sage, Fennel, Thyme, which compete with or inhibit basil growth.
Common Pests and Problems
Basil in Ontario are commonly affected by Aphids, Spider Mite, Fusarium Wilt, Basil Downy Mildew. 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 basil in Ontario?
In Ontario (Canadian Zones 5b–6b), start seeds indoors around March 9 and transplant around May 4. Basil grow well in this province with appropriate variety selection and standard Canadian planting timing.
What is the best basil variety for Ontario?
Ontario gardeners should prioritise varieties bred for shorter seasons or Canadian climates. For basil in Canadian Zones 5b–6b, look for cultivars labelled under 60 days to maturity. Local nurseries and provincial seed exchanges curate varieties that ripen within Canadian frost-free windows.
How does Ontario's climate affect basil?
Ontario spans Canadian Zones 5b–6b with frost-free seasons ranging from roughly 153 to 195 days. Basil 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 basil 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 basil 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 basil plantings in Ontario are spring-timed to harvest before the first fall frost rather than as a second fall crop.