When to Plant Radishes in London, ON
Published: April 24, 2026 · Updated: April 27, 2026
The fastest crop in the garden — ready in 22–30 days. Direct sow 4–6 weeks before last frost and succession plant every 2 weeks for a continuous spring harvest.
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.
Radishes Planting Calendar for London
Direct sow outdoors: March 29–April 8
Harvest window: April 20 – April 28
Minimum soil temperature: 4°C (40°F)
Days to harvest: 22–30 days
Sun requirement: Full sun to partial shade
Fall crop planting: September 15–25 (harvest October 7)
⚠ Direct sow radishes 4–6 weeks before last frost — one of the fastest crops in the garden. Ready in as little as 22 days. Succession plant every 2 weeks for continuous harvest.
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 Radishes
- Thin to 2-inch spacing when seedlings are an inch tall — crowded radishes produce small woody roots.
- Succession plant every 10–14 days from early spring through late spring for continuous harvest.
- Plant as a row marker for slow-germinating crops like carrots — radishes sprout in days and mark the rows.
- Harvest promptly at target size; over-mature radishes turn pithy, woody, and unpleasantly hot.
Companion Planting in London
Pair radish with Lettuce, Carrot, Pea, Cucumber for mutual benefit. Avoid planting near Hyssop, Grape, which compete with or inhibit radish growth.
Pests and Problems to Watch in London
The most common pest and disease pressure on radishes in London comes from Flea Beetle, Cabbage Root Maggot, Aphid. 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 radish in London?
London's last spring frost is around May 3. Direct sow March 29–April 8.
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 radish crop (22–30 days to maturity) before the first fall frost.
Can I grow radish 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 radish crop, plant around September 15–25 so plants mature before the first killing frost.