What to Plant in May in Canada | Zone 5 & 6 Planting Guide

May is the most active planting month for Canadian gardeners in zones 5 and 6. Your last frost date is the pivot point — most of southern Ontario, Quebec, and BC's Lower Mainland falls between May 1 and May 15, which means the first half of May is still a risk window for frost-sensitive crops and the second half opens the door to warm-season planting.

This guide covers what to plant in May in Canada, organized by frost sensitivity and zone, so you can plant with confidence rather than guesswork.

Understanding Your May Frost Window

In zone 5 (much of southern Ontario, southern Alberta, and parts of the Maritimes), the average last frost falls between May 7–15. In zone 6 (southwestern Ontario, southern BC), it arrives earlier — April 15–May 1.

Before planting frost-sensitive crops, check your local frost dates using the MyGardenPlanner frost dates tool. A single late frost can wipe out transplanted tomatoes and peppers.

Early May: Cool-Season Crops Still Going Strong

The first two weeks of May are ideal for finishing your cool-season planting and setting up for summer succession.

Direct sow in early May:

• Lettuce — quick-maturing varieties like 'Black Seeded Simpson' or 'Buttercrunch' can be sown every two weeks through mid-May for continuous harvest
• Spinach — sow thickly now; it bolts once temperatures hit 25°C
• Kale and Swiss chard — cold-hardy, can handle a light frost
• Peas — if you haven't sown yet, do it immediately; peas stall in warm soil
• Beets and carrots — direct sow in prepared beds, thin to 5–7 cm
• Radishes — 25-day varieties make excellent gap-fillers between rows
• Cilantro — bolt-resistant varieties ('Calypso', 'Slow Bolt') work best

Transplant in early May (with frost protection ready):

• Cabbage, broccoli, cauliflower — these brassicas tolerate light frost to -2°C; harden off for 5–7 days before planting out
• Kale starts — same cold tolerance as cabbage

Mid-May: The Transplant Window Opens

Once your local last frost date has passed, the main event begins. Mid-May is when most zone 5 gardeners do the bulk of their warm-season transplanting.

Transplant after last frost:

• Tomatoes — wait until soil is consistently above 12°C at 5 cm depth; cold soil stunts root development even without frost damage. Give each plant 60–90 cm of space depending on variety
• Peppers — need warmer soil than tomatoes (minimum 15°C); in zone 5, late May is safer than mid-May
• Cucumbers — transplant carefully (they dislike root disturbance); use biodegradable pots started 3–4 weeks earlier
• Zucchini and summer squash — direct sow or transplant; grows rapidly once established
• Basil — cold-sensitive; wait until nighttime temperatures are reliably above 10°C

Direct sow in mid-to-late May:

• Beans (bush and pole) — direct sow only (no transplanting); soil must be above 15°C. One of the most rewarding May direct-sow crops
• Corn — needs soil above 10°C; plant in blocks of at least 4 rows for good pollination
• Cucumbers and squash — if direct sowing rather than transplanting

Late May: Warm-Season Push

By late May, zone 5 gardeners can plant nearly anything. Zone 6 gardeners are a week or two ahead of this schedule.

Late May additions:

• Winter squash (butternut, acorn, delicata) — direct sow; needs 80–110 days to maturity, so late May is the latest viable window in zone 5
• Melons — possible in zone 6 and warm zone 5 microclimates with black plastic mulch; start from transplants for best results
• Sweet potato slips — plant 2–3 weeks after last frost when soil is warm; needs a long, warm season — better in zone 6
• Succession lettuce — sow a fresh row every 10–14 days through May for continuous harvest into summer

Zone 5 vs. Zone 6: Key Timing Differences

What to Do While You Wait for Last Frost

The first half of May is not wasted time — use it to:

1. Harden off transplants — move seedlings outdoors in a sheltered spot for increasing periods over 5–7 days before planting
2. Prepare beds — add 2–3 cm of compost, fork in gently, let soil warm
3. Set up support structures — tomato cages, bean trellises, cucumber nets are easier to install before plants are in the ground
4. Mulch bare soil — black plastic or landscape fabric warms soil 2–4°C faster than bare ground

Don't Forget Succession Planting

May is the time to build your succession planting rhythm. Every 10–14 days, sow another row of lettuce, beans, or beets. The MyGardenPlanner succession planting calculator makes it easy to stagger your harvests so you're not drowning in zucchini in July and out of greens by August.

Plan Your Full Season with MyGardenPlanner

The right planting dates in May depend on your specific location and microclimate. Use the planting date calculator at mygardenplanner.ca to get zone-accurate transplant and direct-seeding dates for over 28 crops — customized to your frost dates, not generic US timing that doesn't reflect Canadian conditions.

Start planning your May garden at mygardenplanner.ca.