Now
21°C · Partly cloudy
Today
21° / 9°
Soil 6 cm
14°C
First frost
~11 days (Sep 19)
Gardening in Calgary
AI field guide · refreshed weeklyCalgary Gardening: Early September – Harvest, Protect, and Plan for Frost
You're in zone 4a with 11 days until the average first frost (September 19). Soil at 14°C is cooling fast—root crops and cool-season greens thrive now, but tender annuals are on borrowed time. With only ~121 frost-free days annually, fall is as critical as spring for extending the season and preparing next year.
Sow outdoors now
Spinach (Spinacia oleracea)
Sow 'Space' or 'Bloomsdale Long Standing' directly now; germinates well in 14°C soil and matures in 40–50 days before hard frost.
Arugula (Eruca sativa)
Direct-sow 'Roquette' or 'Wild Rocket'—fast (30 days), cold-hardy, and excellent for fall harvests through mid-October.
Radish (Raphanus sativus)
Sow 'Cherry Belle' or 'French Breakfast' for crisp roots in 25–30 days; cold actually improves flavor.
Mâche (Valerianella locusta)
Direct-sow 'Verte de Cambrai'—extremely cold-hardy, germinates slowly but overwinters well under mulch for spring harvest.
Turnip (Brassica rapa subsp. rapa)
Sow 'Purple Top' or 'Hakurei' now for roots and greens; 60–70 days to maturity, but greens ready in 30 days.
Start indoors now
Cabbage transplants (Brassica oleracea var. capitata)
Start 'January King' or 'Savoy' indoors now (6–8 weeks to transplant); they'll mature in November under frost cloth if needed.
Kale (Brassica oleracea var. acephala)
Sow 'Winterbor' or 'Lacinato' indoors; transplant in 4–5 weeks for harvest through December—frost actually sweetens the leaves.
Onion sets for spring (Allium cepa)
Start 'Walla Walla' or 'Ailsa Craig' from seed indoors now if you missed spring; transplant outdoors in 6 weeks for overwintering.
Harvest now
Tomatoes (Solanum lycopersicum)
Pick all remaining fruit—ripe or mature green—before the first frost; ripen indoors at room temperature or use for salsa and sauce.
Beans and peas (Phaseolus & Pisum sativum)
Harvest bush beans and snap peas now; frost will kill them within days, so pick everything edible.
Squash and pumpkins (Cucurbita spp.)
Cut winter squash and pumpkins with 2–3 cm (1 inch) of stem; cure in a warm, dry place for 10 days before storage.
Root crops (Daucus carota, Beta vulgaris, Solanum tuberosum)
Dig carrots, beets, and potatoes before hard frost; store in cool, dark, humid conditions (0–4°C, 90% RH).
Tasks this week
- Mulch perennial beds and tender shrubs with 5–8 cm (2–3 inches) of compost or straw to insulate roots through winter.
- Cut back dead perennials and ornamental grasses only after hard frost; leave standing for wildlife shelter and winter interest.
- Drain and store garden hoses; shut off outdoor water taps before the first freeze.
- Collect and dry seeds from herbs (dill, cilantro, parsley) and flowers (cosmos, zinnias) for next year.
- Plant spring bulbs (tulips, daffodils, crocus) in well-draining soil; they need 12–16 weeks of cold to bloom.
Watch out for
- First frost is 11 days away—cover tender annuals and late crops with frost cloth on clear, calm nights to buy a week or two.
- Powdery mildew thrives in cool, humid fall weather; thin foliage, improve air flow, and remove infected leaves to prevent spread.
- Grasshoppers and aphids are still active in warm spells; hand-pick or spray with insecticidal soap if populations spike.
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