When to Start Seeds Indoors in Alberta: A Zone-by-Zone Calendar

Find your last-frost date

• Lethbridge, Medicine Hat (Zone 4b): ~May 10–15
• Edmonton, St. Albert, Sherwood Park (Zone 4a): ~May 15–20
• Calgary, Airdrie, Okotoks (Zone 3b/4a): ~May 23–30
• Red Deer, Lacombe, Stettler (Zone 3b): ~May 20–30
• Grande Prairie, Peace River (Zone 3a): ~May 25 – June 5
• Fort McMurray (Zone 2b/3a): ~June 1–10
• Foothills & mountain towns (Jasper, Canmore, Zone 2b/3a): ~June 5–15

These are averages — a cool spring can delay them by a week or more. Check Environment Canada’s historical frost data for your specific postal code for more precision.

12–10 weeks before last frost (late February–early March)

This is slow-germinating territory. Only a few crops need this much head start:

• Onions & leeks from seed — they need the longest season.
• Celery & celeriac — slow, finicky.
• Pansies & violas for early spring bloom.
• Lisianthus — legendarily slow (16 weeks to transplant size).

10–8 weeks before last frost (early–mid March)

• Peppers (sweet and hot) — slow germinators, need warmth (25°C soil) and bright light.
• Eggplant — similar profile to peppers.
• Geraniums — from seed only; cuttings can start anytime.
• Snapdragons for reliably early bloom.

8–6 weeks before last frost (mid March–early April)

The sweet spot for most crops.

• Tomatoes — the home gardener classic. Don’t start too early; leggy indoor seedlings never produce as well as sturdy 6-week-olds.
• Tomatillos — identical timing to tomatoes.
• Kale, Swiss chard, lettuce for early transplant.
• Broccoli, cabbage, cauliflower, kohlrabi — cold-hardy brassicas can go out 2–3 weeks before last frost.
• Petunias, calibrachoa — light-dependent seeds; don’t cover.
• Salvia, rudbeckia, coneflower from seed.

6–4 weeks before last frost (early–mid April)

• Cucumbers, zucchini, summer squash — do NOT start earlier. They sulk if transplanted when overgrown.
• Melons, watermelons — need warm soil to transplant; most of Alberta is marginal for melons.
• Basil — frost-sensitive; start late to avoid indoor leggy growth.
• Cosmos, zinnias, marigolds — could also direct-sow after frost.

Direct-sow after last frost (late May–early June)

These resent transplanting — sow right into the garden:

• Beans (bush and pole), peas (earlier — pre-frost works)
• Corn, sunflowers
• Carrots, beets, parsnips, radishes, turnips
• Nasturtiums, sweet peas, morning glories
• Dill, cilantro (they bolt quickly from transplants)
• Most root vegetables

Alberta native plants — a different timing

Most Alberta native seeds require cold moist stratification— a period of cold wet conditions before they’ll germinate. You have two options:

• Fall-sow directly outdoors (best for most natives) — let winter do the stratification. Sow in October in a prepared bed, mark it well, and watch in spring.
• Indoor cold stratification — mix seeds with damp vermiculite or paper towel in a labelled plastic bag, refrigerate for the species-specific period (usually 30–90 days), then sow indoors in late February.

Some natives need double dormancy(warm-then-cold stratification) — like wild rose and some Prunus species. These are slower and trickier. Check each species’ requirements in our plant catalogue.

Hardening off — don’t skip this step

Indoor seedlings have never felt wind, direct sun, or temperature swings. Moving them straight outside to the garden kills many of them. Spend 7–10 days hardening off:

1. Day 1–2: 1–2 hours outside in a sheltered shady spot.
2. Day 3–4: 3–4 hours, allowing some morning sun.
3. Day 5–7: Most of the day outside, full sun, brought in overnight.
4. Day 8–10: Out day and night in the final spot, if nighttime temps are above 10°C.
5. Transplant on an overcast day if possible, water deeply, and shade the transplants for a couple of days if the sun is intense.

A quick word on grow lights

Alberta’s February–April window has short days, low-angle sun, and limited indoor brightness. South-facing windows are rarely enough for strong seedlings. Spend $40–80 on a basic full-spectrum LED grow light — the difference between leggy pale seedlings and stocky green ones is dramatic. Run 14–16 hours/day; hang it 15–25 cm above the seedlings and raise it as they grow.