Sow hardy Asian greens in Alberta from mid-April to early June, as soon as the soil can be worked, and again from late July to mid-August for a fall crop. The mean last spring frost in Calgary falls on May 21 and the mean first fall frost on September 16. That leaves a short season with cold at both ends, and the crops you choose have to fit inside it.
The short answer for Alberta
Two sowing waves fit Alberta: one in spring, started before the last frost date, and one in late summer, counted back from the first fall frost. Bok choy, tatsoi, mizuna, komatsuna and mustard greens shrug off light frost, so they do not have to wait for May 21 to pass.
Both dates come from Environment and Climate Change Canada’s 1981-2010 climate normals for the Calgary International Airport station. Each is a mean date, the midpoint of a spread of years. In one year out of two, the last spring frost falls later than May 21. In one year out of two, the first fall frost arrives earlier than September 16. The station has about 118 frost-free days between the two dates. Neither date marks a safe moment. They mark the middle of a window, and a hard freeze can land on either side of it.
When can you sow Asian greens in spring in Alberta?
Start as soon as the soil is workable, usually mid-to-late April, and keep sowing in short rows every couple of weeks into early June. Baby leaves of mizuna, tatsoi and mustard greens are ready to cut young. Full heads of pak choi take longer than baby leaves. Seedlings that come up before the last frost need a floating row cover on cold nights, which costs little and helps.
When should you sow Asian greens for fall in Alberta?
Late July through mid-August is the sweet spot. Count back from September 16 and allow for the crop’s time to maturity, plus a margin for a cold, slow September. Fall crops grow in shortening days and cooling nights, which is what these plants like. The Growing Asian Greens in Alberta guide covers the rest of the season, and The Best Asian Greens for Alberta sorts out which types suit each wave.
| Type | Spring sowing | Late-summer sowing |
|---|---|---|
| Baby leaf (mizuna, tatsoi, komatsuna, mustard) | Mid-April to early June, repeated | Late July to mid-August |
| Pak choi heads | Late April to mid-May | Late July to early August |
| Napa cabbage | Not recommended | Mid-July to late July |
What will not work here
Napa cabbage sown in spring will not make a head. Long June days push the plant to bolt before the head forms. Pak choi sown in late May has the same problem. Early sowings finish before the longest days, or the crop waits for the shrinking days of late July.
Which Asian greens fail in Alberta’s short season?
The warm-season types are the ones to skip outdoors. Water spinach and amaranth greens want steady heat, and an Alberta garden with a mean last frost on May 21 and cool nights in the shoulder months does not supply it. The same goes for slow, large-headed napa varieties sown after late July, which run out of days before a hard freeze. Choosing fast types over slow ones matters far more here than in a long-season state.
Why doesn’t winter sowing or overwintering work?
The mean daily minimum of the coldest month is -13.2 °C (8.2 °F). That is far past what any of these greens survive in an open bed. A fall sowing that is too late will not sit dormant and wake up in March. Seedlings that reach winter small will die. Plants that have reached eating size by mid-October can be cut until the hard freezes arrive.
What about dry spells, wind and hail?
Asian greens have shallow roots and stall in dry soil. A once-a-week deep soak from a hose is too little for a crop that goes from seed to harvest in a month, particularly on windy days when chinook air dries a bed in hours. Plan on light watering every day or two while seedlings establish. Summer hail is also a real risk across much of the province, and a low hoop with row cover or mesh saves tender leaves that a storm would shred.
What changes across Alberta
Alberta is not one garden. The Canadian hardiness zone for the reference city is 4a, according to Natural Resources Canada’s 1991-2020 data, and that figure belongs to one municipality. Across the province the zones spread widely, so no single answer covers every reader. Canada’s system draws on seven climate variables, while the USDA system uses one, and NRCan notes that there are no simple conversions between them. Canadian 4a overlaps nine USDA zones, from 3a to 7a. Do not carry the number across the border.
Hardiness zones also say little about timing. Frost dates drive the sowing calendar, and the Calgary dates are one reference point. Northern districts such as the Peace Country and the upland and foothill areas run weeks behind it: later in spring, earlier in fall. Anyone in the north or at higher elevation should shift the calendar. Push spring sowing later by a couple of weeks. Pull fall sowing earlier, and lean on baby leaf crops that finish in about a month. Row cover turns from an extra into a requirement.
The southwest, where chinook winds are frequent, can feel milder in winter but also drier and windier. Greens sown there still bolt in June heat and still need steady moisture. To find your own zone, use the plant hardiness map at Natural Resources Canada’s Plant Hardiness Site and look up your municipality. Then compare it with the reference city.
Where to check this for your own county
Start with Alberta Agriculture and Irrigation, the provincial agriculture department. Look for two things there. First, a local planting calendar or frost-date guide that matches your district rather than the Calgary airport. Second, any list of vegetable varieties trialled in your area, including leafy brassicas such as pak choi and mustard greens. Ask your local agricultural service board or horticultural society whether they hold similar records.
A recommendation for your county beats a recommendation for the province. The dates quoted for Alberta here come from one airport station and from normals that end in 2010, and Canadian normals cover 1981-2010 while US figures cover 1991-2020. Recent springs and falls may have shifted a few days either way. A trial plot near you answers questions that no provincial average can, such as which pak choi bolted and which held.
Checking this against your own garden
Your own observations outrank every date in this article. Three are worth watching, and none needs equipment.
- Soil warmth by feel. Dig a handful of soil a few inches down in April. If it is soggy and cold enough to numb your fingers, wait. Soil that crumbles and feels cool rather than icy is ready. South-facing beds near a wall reach that point days ahead of open ground.
- First true leaves. After the two seed leaves, the first true leaves show whether a sowing is on track. Slow, pale seedlings mean the bed is too cold or too dry. A bed that races to flower stalks early tells you the spot is too hot or too sunny for spring crops.
- Frost on the lawn at dawn. Note which low corners and open patches turn white and which stay clear. Cold air pools in hollows, so those spots set your real last and first frost, which can differ from the regional dates.
Write the dates down for a season or two. A few notes on when you sowed, when the first true leaves appeared and when frost first hit make a calendar built for your own plot.
Common questions
Can I sow bok choy outdoors in April in Alberta?
Yes, once the soil can be worked. Seedlings tolerate light frost, but a hard freeze can still kill them, so keep row cover on hand. Plan to harvest before the long days of late June trigger bolting.
What is the latest I can sow Asian greens for fall?
Mid-August for quick baby-leaf types, with the mean first fall frost on September 16. Heading types such as napa need to go in by late July. A cold September can slow any crop, so sow earlier in northern or upland gardens.
Do I need row cover?
It helps at both ends of the season. In spring it guards seedlings against late frost, and in late summer it keeps flea beetles off young plants and softens the first frosts. It also gives some protection from hail.
Can Asian greens overwinter in Alberta?
No. The mean daily minimum of the coldest month is -13.2 °C (8.2 °F), which kills these plants in an open bed. Treat them as spring and fall crops and sow again each year.