When to Plant Cauliflower in Ontario
Published: April 24, 2026 · Updated: April 27, 2026
Cool-season brassica that bolts in heat above 24°C. Start seeds indoors 4–6 weeks before last frost and transplant 2–4 weeks before last frost. Needs consistent moisture.
Cauliflower grow well in this province with appropriate variety selection and standard Canadian planting timing.
Cauliflower Planting Window for Ontario
Start seeds indoors: March 16–23 (varies by city — earliest in southern Ontario, latest on the Prairies)
Transplant outdoors: March 30–April 9 (after last frost in your city)
Minimum soil temperature: 7°C (45°F)
Days to harvest: 55–100 days
Sun requirement: Full sun (6+ hours)
Fall crop planting: August 23–September 2
⚠ Start cauliflower indoors 4–6 weeks before last frost. Transplant 2–4 weeks before last frost. Needs consistent moisture and cool temps — bolts in heat above 75°F.
Ontario Cities — Cauliflower Planting Dates
City-specific frost dates and cauliflower planting windows for Ontario.
Growing Cauliflower in Ontario
- Blanch white varieties by tying outer leaves over the head when it reaches egg-size — prevents yellowing from sun exposure.
- Keep soil evenly moist — drought stress causes small, bitter 'buttoning' heads instead of full curds.
- Plant fall crops in mid-July to mid-August for October harvest; fall cauliflower is usually larger and sweeter than spring.
- Use floating row covers at transplanting to block cabbage white butterflies from laying eggs.
Companion Planting for Cauliflower
In Ontario gardens, pair cauliflower with Onion, Celery, Dill, Beet. Avoid planting near Tomato, Strawberry, Pepper, which compete with or inhibit cauliflower growth.
Common Pests and Problems
Cauliflower in Ontario are commonly affected by Cabbage Worm, Cabbage Looper, Aphid, Flea Beetle. 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 cauliflower in Ontario?
In Ontario (Canadian Zones 5b–6b), start seeds indoors around March 16 and transplant around March 30. Cauliflower grow well in this province with appropriate variety selection and standard Canadian planting timing.
What is the best cauliflower variety for Ontario?
Ontario gardeners should prioritise varieties bred for shorter seasons or Canadian climates. For cauliflower in Canadian Zones 5b–6b, look for cultivars labelled under 100 days to maturity. Local nurseries and provincial seed exchanges curate varieties that ripen within Canadian frost-free windows.
How does Ontario's climate affect cauliflower?
Ontario spans Canadian Zones 5b–6b with frost-free seasons ranging from roughly 153 to 195 days. Cauliflower actually prefer the cooler spring and fall windows typical of Ontario, making them one of the most reliable crops in the province.
Can I grow cauliflower 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 cauliflower 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. For a fall cauliflower crop, count back from your local first-frost date and plant around August 23–September 2.