Sow Asian greens outdoors in the Northwest Territories from late May to late July, in small batches every two weeks. Start the first batch under cover, because late May is the average last frost and half of all years run later. A hard fall frost ends the run, so the last sowings are fast baby-leaf types. Adjust these dates for your own community.
The short answer for Northwest Territories
At the Yellowknife A station, the last spring frost falls on average on May 25 and the first fall frost on average on September 18 (Environment and Climate Change Canada, 1981-2010 normals). Both are mean dates. In one year out of two, the last frost comes later than May 25, and in one year out of two, the first frost arrives earlier than September 18. The station has about 116 frost-free days between the two dates. Treat each date as the middle of a window.
Asian greens suit that window. Mizuna, tatsoi, komatsuna and baby bok choy are cool-season crops grown from seed sown directly in the bed. Seedlings shrug off a light frost, which lets you plant ahead of the mean date. They do not shrug off a hard freeze. Our overview of Growing Asian Greens in Northwest Territories covers the crop as a whole, and the dates below cover the calendar.
When can you sow Asian greens outdoors in the Northwest Territories?
Sow under a row cover or low tunnel from mid-May if the soil has thawed and drained. Sow uncovered from about May 25 onward, ideally in the days after a stretch of mild nights. Waiting a week past the mean date costs little, because these greens catch up fast once the beds warm. A frost that kills seedlings in early June costs a full resowing.
| Type | First sowing | Last sowing | Sowing to harvest |
|---|---|---|---|
| Baby leaf (mizuna, tatsoi, komatsuna) | Mid-May under cover, about May 25 uncovered | Late July to early August, with cover | Roughly 3 to 5 weeks |
| Baby and full-size bok choy | About May 25, earlier under cover | Mid-July | Roughly 4 to 8 weeks |
| Heading Chinese cabbage | Under cover only | Early July at the latest | Often two months or more |
When is the last good sowing date?
Count back from September 18. A baby-leaf crop needing five weeks must go in by about August 12 to beat the mean frost, and sooner if you want leaves of real size. Daylight shortens quickly in late summer this far north, so growth slows well before the frost arrives. Late July is a safer cutoff, and a row cover buys a few extra days at either end. For picking varieties that fit these windows, see The Best Asian Greens for Northwest Territories.
What will not work here
Heading Chinese cabbage is the first casualty. Napa types often take two months or more from sowing, and they want cool weather on both ends. With roughly 116 frost-free days at the reference station and a cold, slow spring, that leaves little room. Sown in early July, a napa head has to finish before the mean frost on September 18, in a year when that date may arrive early. It is a gamble, and it pays off only under cover.
Sowing on a warm day in early May fails for a simpler reason. May 25 is the midpoint, so frost after that date happens in about half of all years. Seedlings that emerged in a mild week can be flattened by a late freeze. Even where they survive, a run of cold nights in the seedling stage can push Asian greens to bolt, which means they send up a flower stalk instead of making leaves.
Midsummer brings a different problem. Long days are a bolting signal for many Asian greens. Plants sown in May and left to size up around the solstice are the ones that run to seed. Pick them as baby leaf or young heads, and save the large sowings for early to mid July, when days begin to shorten.
Overwintering fails outright. The mean daily minimum of the coldest month is -29.5 °C (-21.1 °F). Gardeners in milder parts of the United States leave hardy greens in the ground through winter and pick them in spring, and that habit does not travel north. Nothing in open ground here survives such months. A greenhouse that is unheated through the cold season does no better.
Direct sowing into cold, wet soil also fails. Seeds that sit in saturated ground below the temperatures they like germinate slowly and unevenly, and some rot. Soil that has thawed but not drained is the usual culprit. A raised bed with free-draining soil warms sooner than flat ground and gives seed a fair start.
What changes across Northwest Territories
The reference station’s frost dates describe one airport, and the territory is long. It runs from the south Slave region at about 60°N up to the Arctic coast at the Mackenzie Delta, well above the Arctic Circle. No single sowing date fits that spread. Yellowknife’s hardiness zone is 1b in the Canadian system, and that figure belongs to the reference city, not the territory.
The Canadian system is not a USDA zone and does not convert to one. Natural Resources Canada builds it on seven climate variables, while the USDA map uses winter minimum temperature alone. NRCan itself says there is no simple conversion, and its own example is a Canadian zone 4a that overlaps nine USDA zones, from 3a to 7a. When a Canadian zone appears in a seed catalog or on a plant tag, read it as a Canadian number. The frost dates here cover 1981-2010, and the hardiness map covers 1991-2020, so the two will not line up exactly.
For your own community, look it up on Natural Resources Canada’s Plant Hardiness Site. That map will tell you where you sit, and it beats any guess from a neighbor two valleys away.
The practical shift is simple. Northern communities and upland districts run weeks behind Yellowknife. If your spring thaw comes a week later, move every date in the table back by a week. Lean harder on baby leaf, which finishes fastest, and drop heading types altogether. Row cover and low tunnels matter more the farther north you go. Communities in the south of the territory may run somewhat ahead of the reference station, but a warm spell in April is no reason to sow before the soil has thawed and drained.
Where to check this for your own county
The Northwest Territories has no counties, so the local level is your community or region. Start with the Government of the Northwest Territories, Department of Industry, Tourism and Investment, which runs the territory’s agriculture services. Ask for the following:
- A planting calendar written for your community, or the nearest one with a weather station
- Frost dates for that station, and how far they run from Yellowknife’s
- Which Asian greens have been grown successfully nearby, and which have failed
- Whether growers in your area start under cover, and how early
A recommendation for your own community beats a territorial one, because a territory-wide calendar averages places that differ by weeks. Treat the dates above as a starting point. If a local grower or agriculture officer tells you the soil near you thaws two weeks later, believe them. If they name a variety that bolted every year, skip it.
One more thing is worth asking about: how local growers handle the long daylight. Gardeners who have worked a particular valley for years know which sowing dates bolt and which give a clean harvest, and that knowledge rarely makes it into printed calendars.
Checking this against your own garden
Your own beds outrank every date above. Three things are worth watching each spring, and none needs equipment.
First, feel the soil. Push your hand two inches into the bed in the morning. If the ground feels cold enough to ache within a minute, hold off, or sow under cover. A bed that feels cool but bearable is ready for Asian greens. A south-facing raised bed or one beside a wall or rock usually passes this test days ahead of open ground, and that gap is your microclimate.
Second, watch the willows and birches. When willow catkins open, those are the male flowers, and when birch buds break, the ground is usually thawed and the worst of the hard freezes is behind you. Note the date each year. After two or three springs, your own bud-break date will track your garden better than any airport station.
Third, check the first true leaves. A seedling’s first pair of leaves are seed leaves. The true leaves come next, with the shape of the mature plant. If seedlings sit at the seed-leaf stage and do not move on, the soil is too cold, and a cover or a later sowing will serve better.
Common questions
Can I sow Asian greens before the last frost in the Northwest Territories?
Yes, under a row cover or low tunnel, once the soil has thawed and drained. The mean last frost at Yellowknife A is May 25, so in half of years frost comes later. Seedlings tolerate light frost, but a hard freeze can kill them.
How often should I sow?
Every two weeks from late May to late July works well. Small batches spread the harvest and hedge against a frost, a bolting spell or a poor stretch of weather. Early sowings that mature near the solstice are the most likely to bolt.
Will bok choy survive a frost?
It handles a light frost, and a cover adds some margin. A hard freeze ends it. Before the first fall frost, which averages September 18 at the reference station, harvest what you can or cover the bed.
Do I need a greenhouse?
No. A row cover or low tunnel is enough for most sowings, and a greenhouse gives the earliest start. Neither makes heading Chinese cabbage a safe crop here. Keep to fast baby-leaf types and bok choy, and you can grow a good crop without one.