When to Plant Cucumbers in London, ON
Published: April 24, 2026 · Updated: April 27, 2026
One of the fastest-growing vegetables — ready to harvest in 50–70 days. Cucumbers can be direct-sown after last frost and often outproduce transplanted seedlings.
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.
Cucumbers Planting Calendar for London
Start seeds indoors: April 12–19
Transplant outdoors: May 10–20
Direct sow outdoors: May 10–20
Harvest window: June 29 – July 19
Minimum soil temperature: 16°C (60°F)
Days to harvest: 50–70 days
Sun requirement: Full sun (8+ hours)
Fall crop planting: August 11–21 (harvest September 30)
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 Cucumbers
- Direct sow after last frost rather than transplanting — cucumbers establish faster from seed in warm soil.
- Trellis vertically to save space and reduce powdery mildew from soil splash.
- Harvest every 2–3 days — cucumbers left on the vine signal the plant to stop producing new fruit.
- Water deeply and consistently; drought stress causes bitter flavor and hollow centers.
Companion Planting in London
Pair cucumber with Radish, Nasturtium, Dill, Bush Beans for mutual benefit. Avoid planting near Aromatic Herbs, Potato, Sage, which compete with or inhibit cucumber growth.
Pests and Problems to Watch in London
The most common pest and disease pressure on cucumbers in London comes from Cucumber Beetle, Squash Vine Borer, Powdery Mildew, Aphids. 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 cucumber in London?
London's last spring frost is around May 3. Start seeds indoors April 12–19. Transplant outdoors May 10–20.
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 cucumber crop (50–70 days to maturity) before the first fall frost.
Can I grow cucumber 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. For a fall cucumber crop, plant around August 11–21 so plants mature before the first killing frost.