How to Grow Broccoli in Canada: Spring and Fall Planting Guide

Why Grow Broccoli in Canada?

Broccoli is a cool-season powerhouse that suits the Canadian climate extremely well. When timing is right -- transplanted into cool soil in spring or late summer -- broccoli grows vigorously, produces large, tight heads, and then keeps delivering side shoots for weeks. Fresh broccoli from the garden has a sweetness and tenderness that grocery store broccoli, cut days or weeks earlier, simply cannot match.

The critical insight for Canadian gardeners is that broccoli needs cool temperatures to head up properly. Heat causes the plant to rush to flower -- a process called bolting -- before a head fully forms. This means planting is not about finding the warmest conditions, but about timing transplants to mature in the cool shoulder seasons of spring and fall.

Understanding Broccoli's Relationship With Temperature

Broccoli grows best when daytime temperatures are 15 to 20 C (60 to 68 F). It tolerates light frost well -- established plants can handle temperatures as low as -5 C (23 F) briefly -- and actually tastes sweeter after a light frost, as starches convert to sugars.

The problem comes from heat. When temperatures exceed 26 to 28 C (80 to 82 F) for extended periods, broccoli heads open (turn yellow) and bolt rapidly. This is why summer-planted broccoli almost always fails in most Canadian zones -- the plants head up in July heat and bolt before heads size up.

The solution is to plan around heat: transplant spring broccoli early enough that heads form before the summer heat of July, or start a fall crop in late summer to head up in the cool of September and October.

Spring vs Fall Planting Strategy

Spring planting is the primary approach for most Canadian gardeners. Start seeds indoors 4 to 6 weeks before the last frost date. Transplant to the garden 2 to 4 weeks before last frost -- broccoli handles frost well. The goal is to have heads forming in June, before the heat of July arrives.

Fall planting extends the broccoli season and is well worth attempting in zones 5 and warmer. Count backwards from your first expected fall frost date: broccoli needs 60 to 80 days to maturity, plus 4 to 6 weeks of seedling time if starting from seed. For most of southern Ontario, Quebec, and BC, this means starting fall transplants in late June to mid-July for September and October harvests.

Prairie gardeners (zones 3 and 4) typically have time for a spring crop but not a reliable fall crop, given the early frosts. Focus on spring planting with fast-maturing varieties.

When to Plant by Province

Spring planting (start indoors, then transplant):

• British Columbia (coastal, Zone 8): Start indoors late February; transplant mid to late March
• Southern BC Interior (Zones 5-6): Start indoors early March; transplant late April
• Southern Ontario (Zones 5-6): Start indoors early to mid-March; transplant late April to early May
• Quebec (Zones 4-5): Start indoors mid-March; transplant early to mid-May
• Maritimes (Zones 5-6): Start indoors mid-March; transplant early to mid-May
• Prairies -- Manitoba/Saskatchewan (Zones 3-4): Start indoors early to mid-April; transplant mid to late May
• Alberta (Zones 3-4): Start indoors mid-April; transplant late May to early June

Fall planting (zones 5 and warmer): Start transplants indoors or in a sheltered nursery bed in late June to mid-July. Transplant to the main garden in late July to early August for September and October harvests.

Check frost dates for your location and use our garden calculator for precise dates.

Starting Seeds Indoors

1. Sow seeds 6 mm (0.25 inch) deep in seedling mix. Broccoli germinates quickly -- 5 to 7 days at 18 to 24 C (65 to 75 F). A heat mat is helpful but not essential; broccoli germinates in cool conditions better than most crops.
2. Cool growing conditions suit broccoli seedlings. Grow at 15 to 18 C (60 to 65 F) under lights. Warmer temperatures produce leggy, weak seedlings. A cool basement or garage windowsill is often ideal.
3. Pot up to 10 cm (4-inch) pots once the first true leaves appear.
4. Harden off for 7 to 10 days before transplanting, gradually exposing seedlings to outdoor conditions.

Spacing in 30-Inch Beds

Broccoli is a large plant. Give it adequate room for big heads and good airflow.

Two rows at 45 cm (18-inch) spacing is standard. A 3.6 m (12-foot) bed holds 8 plants. For very large-heading varieties, increase to 50 to 60 cm (20 to 24 inches) spacing. Side shoot production after the main head is harvested benefits from slightly wider spacing and better airflow.

Growing Tips

Soil. Broccoli is a heavy feeder requiring rich, fertile, well-drained soil with a pH of 6.0 to 7.0. Work in generous compost before planting. Side-dress with nitrogen fertilizer or liquid fish emulsion 3 weeks after transplanting to fuel leaf and head development.

Watering. Consistent moisture produces the largest, tightest heads. Aim for 2.5 cm (1 inch) per week. Drought stress causes premature heading and bitterness. Water at the base of plants; wet foliage promotes fungal diseases.

Cutworm protection. Cutworms sever transplants at the soil line overnight, destroying seedlings. Protect every transplant with a collar: a section of cardboard tube, a plastic cup with the bottom cut off, or even a strip of cardboard formed into a ring. Push the collar 2.5 cm (1 inch) into the soil and extend 5 cm (2 inches) above. This simple step prevents nearly all cutworm damage.

Cabbage moth and cabbage looper. The larvae of these moths (small green caterpillars, sometimes called cabbageworms) are broccoli's most damaging pest in Canada. They eat holes in leaves and burrow into developing heads. The most effective prevention is floating row cover -- a lightweight fabric draped over plants and sealed at the edges with soil or clips. Cabbage moths cannot lay eggs on protected plants. Apply row cover at transplant time and leave it in place until harvest if desired (broccoli does not need insect pollination).

If caterpillars are found despite preventive measures, apply Bacillus thuringiensis (Bt), a naturally occurring bacterial insecticide that targets caterpillars and is approved for organic production.

Crop rotation. Rotate broccoli and all other brassicas (cabbage, cauliflower, kale, kohlrabi) to a different bed each year. This breaks cycles of clubroot, a devastating soil-borne disease that causes stunted, yellowing plants. Once clubroot is established in a bed it is extremely difficult to eradicate; prevention through rotation is essential.

Harvesting the Main Head and Side Shoots

This is where many first-time growers miss out on weeks of additional harvest.

Main head: Harvest when the head is tight, deep green, and before individual flower buds begin to open and show yellow. A head that is starting to go yellow has begun to bolt -- harvest immediately regardless of size. Cut the main stem 10 to 15 cm (4 to 6 inches) below the head with a sharp knife.

Side shoots: After the main head is cut, most broccoli varieties -- especially indeterminate types -- produce a flush of small side shoot heads from the leaf axils. These are sweet, tender, and can be harvested over 4 to 8 weeks. Keep cutting regularly; like beans, broccoli continues producing side shoots as long as they are harvested before bolting.

Side shoot production is a compelling reason to choose varieties known for their side shoot yield, not just main head size.

Recommended Varieties for Canadian Gardens

• Waltham 29 -- Open-pollinated classic; large main head; excellent side shoot production; reliable and widely available
• Green Magic -- Hybrid; 60 days; tight, domed heads; good heat tolerance and bolting resistance; one of the best spring varieties for Canadian conditions
• Marathon -- Hybrid; 68 days; large, uniform heads; very good disease resistance; widely grown commercially in Canada
• Fiesta -- Hybrid; 64 days; good heat tolerance; strong side shoot production; well-suited to zones 5 and warmer
• Gypsy -- Hybrid; 60 days; fast-maturing; good choice for Prairie gardeners and short-season zones; produces under cool conditions
• Belstar -- Hybrid; 65 days; dense, blue-green heads; excellent cold tolerance; good fall variety; holds well without bolting in cool conditions

Seeds available from William Dam Seeds, Stokes Seeds, West Coast Seeds, and OSC Seeds.

Plan Your Broccoli Garden

Our free garden calculator calculates both spring and fall planting windows for broccoli based on your frost dates. For information on pairing broccoli with companion crops and planning a full brassica rotation, see our companion planting guide.