Asian greens grow in the Northwest Territories as a quick crop that runs from late spring to early fall. At Yellowknife A, the average last spring frost is May 25 and the average first fall frost is September 18. That leaves room for one sowing of fast types and, with good timing, a second. The things that decide success are warm soil, bolting control and a finish before the first hard freeze.
When the soil is warm enough in Northwest Territories
The anchor date is May 25. It is the average last spring frost at the Yellowknife A station, taken from Environment and Climate Change Canada’s Canadian Climate Normals for 1981-2010. An average is a midpoint, so in about one year out of two the last frost falls later. Northern districts, the Mackenzie Delta for example, run weeks behind Yellowknife. A gardener there should push every date back.
Frost date and planting date are two separate questions. Asian greens wait for warm soil, and soil warms after the frost risk has ended. Seed sown into cold, wet ground sits and sometimes rots. Seedlings that take a long cold spell early can also be pushed toward bolting, which means they send up a flower stalk before they have made a useful head or rosette of leaves. In a short season, that loss is hard to recover.
How do you tell when the soil is ready?
Start with the ground itself. It must be fully thawed, drained and crumbly in your hand rather than slick or clotted. Then push a soil thermometer a couple of inches down and read it at the same hour for several days. You want a steady climb, not one warm afternoon. Many Yellowknife gardeners grow in raised beds, because natural soil over bedrock is thin and slow to warm, and a raised bed with dark soil is usually the first to thaw and drain.
Sow in the days after the average date has passed instead of before it. If the forecast shows a cold snap, a floating row cover over the bed holds a few degrees of warmth at night. Gardeners elsewhere run on very different calendars. The Growing Asian Greens in Colorado guide shows how much earlier a lower-latitude start can be. The Canadian normals also cover 1981-2010, an older period than the 1991-2020 normals used for US sites, so treat the date as a guide and not a promise.
How long the season lasts here
The reference station has about 116 frost-free days between the mean last spring frost on May 25 and the mean first fall frost on September 18. Both dates are averages, so in roughly half of all years the first frost arrives earlier than September 18.
That window is short, and it settles several choices. Fast, small types such as baby bok choy and tatsoi can finish one sowing with room to spare. A second sowing in midsummer, timed to mature in the cooler weeks of late August and early September, is possible with those same quick types. Slow, heading types such as napa cabbage have little margin. A late start or an early freeze can leave you with heads that never close.
Plan on small, repeated sowings instead of one big block. A short row every couple of weeks through early summer spreads the harvest and hedges against a single batch bolting in a hot or cold spell. The succession sowing guide on this site lays out the spacing and the cut-off dates in more detail. Count backward from mid-September, and stop sowing a type once it can no longer finish before frost.
Short seasons also change the transplanting question. Many Asian greens resent root disturbance, and a check at transplanting can trigger bolting. Starting seed indoors in paper or peat pots, so the roots stay intact, can gain you a week or two. For the fastest types, direct sowing is simpler and often just as quick. In a window this narrow, transplants earn their place mainly for the slower heading types. For a general overview, see Growing Asian Greens: Fast, Cold-Hardy, and Prone to Bolting. Gardeners farther north will find a still shorter calendar in Growing Asian Greens in Nunavut.
Heat and water in Northwest Territories
Summer heat is rarely the problem at Yellowknife A. Days above 90°F are uncommon at this latitude, so the shade-cloth and root-cooling tactics gardeners use farther south are seldom needed. This family belongs to the second half of the growing season, and the facts that govern it are the first fall frost and the winter low. The first fall frost averages September 18 at the station, and that date sets how late a sowing can still finish. The coldest month has a mean daily minimum of -29.5°C (-21.1°F).
Where summer heat is mild, other problems take its place. A cool, damp stretch brings mildew on the leaves, slow growth and soft rot at the base of the plant. Leaves that stay wet overnight invite disease, so water at the soil line in the morning and give plants room for air to move. A dry spell is the other risk. Uneven moisture makes leaves bitter and pushes plants toward bolting, so mulch lightly to keep the bed evenly damp.
Disease deserves one more warning. Bok choy, mizuna, mustard greens and napa cabbage are brassicas, and so are turnips and rutabagas. They all share their pests and diseases with cabbage, kale and broccoli. A bed that grew cabbage last year is not a fresh bed for Asian greens, so rotate them to ground that has been free of the whole family for a few years.
Can Asian greens survive a Northwest Territories winter?
Not in open ground. Yellowknife sits in Canadian hardiness zone 1b (a Canadian system that does not convert to USDA zones), and a mean daily minimum of -29.5°C in the coldest month is far past what any Asian green tolerates. A cover does not change the outcome. The season ends with the first hard freeze, and the most a row cover or low tunnel can do is stretch the harvest a few weeks past the first light frosts. Anything left in the bed after a hard freeze should be cleared, not hoped over.
Which Asian greens suit Northwest Territories
A short season favors the earliest types, and cool summers make disease resistance and good airflow the first things to look for. Heat tolerance matters far less here than quick maturity and resistance to bolting. Choose by type first, then check which varieties local growers rely on.
| Type | Fit for a short northern season | What to watch |
|---|---|---|
| Baby or small bok choy | Quick and compact, suited to two sowings | Bolts after cold snaps or in long, dry spells |
| Tatsoi and mizuna | Fast and cold tolerant, good for early and late sowings | Mildew in damp weather, so thin for airflow |
| Mustard greens | Quick leaf crop, tolerates cool nights | Share diseases with cabbage and kale |
| Napa cabbage | Needs the full window and little margin | Heads may not close before frost |
Look at the whole list through the first frost date. A type that needs most of the 116 frost-free days leaves no room for a late spring or an early autumn. Fast types forgive both. If you do grow napa or another heading type, harvest before a hard freeze and inspect each head before storing it. A soft patch, a weeping spot or a moldy crown ends the question, and that head goes to the compost, not the fridge.
Variety names are left out here on purpose. A seed packet shows how a variety behaved somewhere else, and the useful answer is the one trialled in northern gardens like yours. The Government of the Northwest Territories agriculture services can point you to what local growers rely on, and a local nursery or garden group can fill in the details for your community.
Common questions
When should I sow Asian greens in Yellowknife?
Sow after the soil has thawed, drained and warmed steadily, which usually falls after the average last frost of May 25. Since half of years run later, watch the soil and the forecast instead of the calendar.
Can I leave Asian greens in the ground over winter?
No. The coldest month averages a daily low of -29.5°C (-21.1°F), and even a protected bed will not carry these crops through. Cover can stretch the harvest past the first light frosts, but a hard freeze ends it.
Are turnips and rutabagas safe to rotate into a cabbage bed?
No. Turnips and rutabagas are brassicas, and they share pests and diseases with cabbage, kale and mustard. Rotating one into another’s bed leaves the soil problems exactly where they were. Move the crop to ground that has been clear of the family for several years.
Where can I find the right varieties for my area?
Ask the Government of the Northwest Territories agriculture services about varieties grown in northern conditions, and compare notes with local growers. Their experience across several seasons is worth more than any packet label.