Month-by-month guide to what to start indoors, direct sow, transplant, and harvest — built for Alberta's short, intense growing season.
May is Alberta's most dynamic gardening month. Early May brings cold-hardy transplants outdoors; the May long weekend is the cultural signal for potatoes; and after last frost, the full planting season opens. Keep row cover close — a surprise frost can wipe out tender plants overnight.
Broccoli, cauliflower, Brussels sprouts, kohlrabi, and cabbage can be direct-sown in early May — they tolerate frost to -3°C and actually prefer cool weather. Space 45 cm apart. Brussels sprouts need full season: direct sow by May 15 at the latest in most of Alberta.
Sow beets once soil reaches 10°C. Each 'seed' is actually a cluster of 2–4 seeds, so thin ruthlessly to 8 cm or you'll get all tops, no roots. Swiss chard is more forgiving and can be cut repeatedly all season.
Direct sow kale as soon as soil is workable — it's one of Alberta's best crops, especially in fall when frost sweetens the leaves. 'Winterbor' (curly), 'Red Russian' (tender), 'Lacinato' (dinosaur kale). Asian greens like pak choi and mizuna bolt quickly in heat — best in spring and fall.
Don't plant beans until soil reaches 18°C — cold soil causes rot. After your region's last frost, direct sow 5 cm deep, 8 cm apart. Beans grow fast and don't like transplanting. Bush beans mature in 50–55 days — enough time for two sowings in most of Alberta.
Corn needs warm soil and Alberta's long summer days to mature. Direct sow after last frost in blocks of at least 4 rows for wind pollination — rows, not scattered plants. Short-season varieties only.
All three are sown directly after last frost. Zucchini grows aggressively under Alberta's long days — one or two plants is usually enough per family. Sunflowers attract pollinators and seed-eating birds in fall. Nasturtiums have edible flowers and leaves and deter aphids from cucumbers.
Pansies, snapdragons, and brassica transplants (broccoli, cauliflower, cabbage) can go outside in early May, weeks before last frost. Harden off for 7–10 days first. Use row cover for overnight protection if temps drop below -5°C.
The main event. Plant after last frost, when nighttime temps consistently stay above 10°C. Bury tomato transplants deep — up to 2/3 of the stem — they root all along the buried stem. Warm the soil with black plastic mulch 1–2 weeks ahead for earlier production.
These are the most cold-sensitive crops. Wait until after last frost — even a light frost will set them back significantly. Cucumbers especially need warm soil (above 18°C) to establish well. Transplant on a cloudy day to reduce transplant shock.
Victoria Day weekend is Alberta's traditional potato planting signal. Soil should be at least 10°C. Cut seed potatoes into pieces with 2+ eyes, let cut surfaces cure for 2–3 days. Plant 10–15 cm deep, 30 cm apart. Hill soil around stems every few weeks as plants grow.
Alberta can see killing frost well past the 'last frost date' — these are historical averages, not guarantees. Keep floating row cover (Reemay or similar) handy through May. Check Environment Canada's 7-day forecast before planting tender crops.
Historical averages — always check Environment Canada forecasts.