When to Plant Cauliflower in Ottawa, ON
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.
Ottawa's Canadian Zone 5b (USDA 5a) continental climate brings cold winters, hot summers, and higher frost risk than Toronto thanks to the inland location. The 153 frost-free days from early May through early October is adequate for most vegetables, but variety selection — short-season cultivars under 70 days — matters significantly.
Cauliflower Planting Calendar for Ottawa
Start seeds indoors: April 1–8
Transplant outdoors: April 15–25
Harvest window: June 9 – July 24
Minimum soil temperature: 7°C (45°F)
Days to harvest: 55–100 days
Sun requirement: Full sun (6+ hours)
Fall crop planting: July 28–August 7 (harvest September 21)
⚠ 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.
Ottawa Climate Notes
Ottawa Valley winters are harsh. Choose short-season tomato varieties under 70 days (Stupice, Sunrise, Sub-Arctic Plenty) and transplant only after the May long weekend. Fall garden extends the productive season into October with cold-tolerant greens and brassicas.
Growing Tips for Cauliflower
- 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 in Ottawa
Pair cauliflower with Onion, Celery, Dill, Beet for mutual benefit. Avoid planting near Tomato, Strawberry, Pepper, which compete with or inhibit cauliflower growth.
Pests and Problems to Watch in Ottawa
The most common pest and disease pressure on cauliflower in Ottawa comes from Cabbage Worm, Cabbage Looper, Aphid, Flea Beetle. Floating row covers through the first 4–6 weeks after planting block adult pests from laying eggs, and a weekly scouting routine catches infestations before they damage the crop.
Other Ontario Cities
Frequently Asked Questions
When do I plant cauliflower in Ottawa?
Ottawa's last spring frost is around May 6. Start seeds indoors April 1–8. Transplant outdoors April 15–25.
What Canadian hardiness zone is Ottawa?
Ottawa is in Canadian Zone 5b (USDA equivalent 5a). The continental inland climate delivers 153 frost-free days from May 6 to October 6, which shapes every planting date in the local calendar.
How long is Ottawa's growing season?
Ottawa has 153 frost-free days — from May 6 in spring to October 6 in fall. That is more than enough time to finish a full cauliflower crop (55–100 days to maturity) before the first fall frost.
Can I grow cauliflower in containers in Ottawa?
Yes. Container growing on balconies and decks is practical in Ottawa — choose a 5-gallon or larger dark-coloured container to warm the root zone, use a high-quality potting mix, and water daily during hot summer weather. In milder climates, containers extend both spring and fall windows by several weeks.
What is the first fall frost in Ottawa?
Ottawa's average first fall frost is October 6. For a fall cauliflower crop, plant around July 28–August 7 so plants mature before the first killing frost.