When to Plant Basil in London, ON
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.
London's Canadian Zone 6a (USDA 5b) southwestern Ontario climate delivers adequate rainfall, warm summers, and 170 frost-free days. Shorter than Toronto's season but long enough for reliable production of most warm-season crops with appropriate variety selection.
Basil Planting Calendar for London
Start seeds indoors: March 22–29
Transplant outdoors: May 17–27
Direct sow outdoors: May 17–27
Harvest window: June 16 – July 16
Minimum soil temperature: 16°C (60°F)
Days to harvest: 30–60 days
Sun requirement: Full sun (6+ hours)
London Climate Notes
London has 150-170 frost-free days — adequate for most warm-season crops when transplants go in by late May. The region's rich soils support heavy feeders like tomatoes and brassicas with minimal amendment.
Growing Tips for Basil
- 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 in London
Pair basil with Tomato, Pepper, Marigold, Oregano for mutual benefit. Avoid planting near Sage, Fennel, Thyme, which compete with or inhibit basil growth.
Pests and Problems to Watch in London
The most common pest and disease pressure on basil in London comes from Aphids, Spider Mite, Fusarium Wilt, Basil Downy Mildew. 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 basil in London?
London's last spring frost is around May 3. Start seeds indoors March 22–29. Transplant outdoors May 17–27.
What Canadian hardiness zone is London?
London is in Canadian Zone 6a (USDA equivalent 5b). The southwestern Ontario temperate climate delivers 170 frost-free days from May 3 to October 20, which shapes every planting date in the local calendar.
How long is London's growing season?
London has 170 frost-free days — from May 3 in spring to October 20 in fall. That is more than enough time to finish a full basil crop (30–60 days to maturity) before the first fall frost.
Can I grow basil in containers in London?
Yes. Container growing on balconies and decks is practical in London — 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 London?
London's average first fall frost is October 20. Most basil in London is a single spring-timed planting designed to harvest before the first fall frost.