Sow Asian greens in Yukon from mid-May under cover, or outdoors from about June 5, and stop in the first week of July. The fast, leafy types (mizuna, tatsoi, komatsuna, baby bok choy) fit the short season well. Heading types and big slow varieties leave almost no margin. For the full list of what to grow, see The Best Asian Greens for Yukon.
The short answer for Yukon
The sowing window runs from mid-May, under row cover or in a tunnel, to about the first week of July. Outdoors with no protection, the sensible start is around June 5. That date is the average last spring frost at the Whitehorse A station, from Environment and Climate Change Canada’s 1981-2010 normals. It is a midpoint, and in one year out of two the last frost falls later. Hardy greens can go in ahead of it under cover. Tender or slow ones should wait until the date has passed.
The other end of the window works the same way. The average first fall frost is August 25, so in one year out of two it arrives earlier. The station has about 81 frost-free days between the two dates. A crop sown on July 7 that needs 45 days would finish right at the edge, which is why early July is the cutoff for anything that takes more than a month.
Why sowing late June can beat sowing in May
Many Asian greens read long days as a signal to flower, and an early sowing that matures in June light often sends up a seed stalk before it makes a decent harvest. Sowings from mid-June to early July mature as days shorten, and they tend to stay leafy longer. If you can only sow once, late May to mid-June is a sound compromise.
| Type | Sowing window | Notes |
|---|---|---|
| Mizuna, tatsoi, komatsuna | Mid-May under cover to first week of July | Hardy, fast, cut young as baby leaves |
| Baby bok choy | From about June 5 outdoors, or earlier under cover, to early July | Harvest small, well before the frost window |
| Full-size bok choy | Late May under cover to mid-June | Needs more weeks, so start early |
| Napa cabbage | Start under cover, set out after about June 5 | Marginal; heading takes most of the season |
Our overview, Growing Asian Greens in Yukon, covers site, soil and care once the seed is in.
What will not work here
Heading napa cabbage and any variety with a long packet count are the first to fail. If a variety needs a long season, a cool June or an early frost ends the crop before it forms. Seed packets count days from sowing for direct-sown greens, and from transplanting only for seedlings you set out. Check which one the packet means.
Sowing in early May without protection also disappoints. The coldest month here averages a daily minimum of -19.2 °C (-2.6 °F), and the ground is slow to give up that cold. Seed sits in cold soil, germinates unevenly, and rots in a wet spell. A bed under clear plastic or fabric warms sooner, but a May cold snap can still strike, so keep the cover on until the weather settles.
A southern-style second sowing in late July or August is another miss. In much of the country, fall is the best season for Asian greens. Here the average first frost on August 25 leaves too little time for seed sown after early July to reach harvest size. Tatsoi and mizuna tolerate light frost, but a hard freeze ends them, and short days slow growth to a crawl by September.
Trusting June 5 as a safe date is a quieter mistake. It is the middle of the range, so half of all years bring a frost after it. Greens sown right on that date with no cover are gambling on the better half of the years. Keep a sheet of fabric on hand for the first weeks.
Other problems are bolting in long days, as described above, and flea beetles. These small beetles chew shot holes in brassica leaves, and a young seedling in a short season has little time to recover. Floating row cover laid over the bed at sowing is the standard defense. Dry spells matter too. Shallow-rooted greens that dry out between waterings turn bitter and bolt sooner, so steady moisture is worth more than heavy watering once a week.
What changes across Yukon
The reference city, Whitehorse, sits in hardiness zone 1b on Natural Resources Canada’s system, using 1991-2020 normals. That is the Canadian system, which draws on seven climate variables. It does not convert to a USDA zone, and Canadian zone 4a alone overlaps nine USDA zones, from 3a to 7a. Do not carry a USDA number into a Yukon calendar.
That zone belongs to one city, not the whole territory. Yukon spans a large range of latitude and elevation, so there is no single answer. The frost dates above come from one airport station, and northern or upland districts run weeks behind it. In a valley bottom, cold air pools on clear nights and frost comes earlier than on a slope a short distance up.
What should a reader farther north, or higher up, change? Shift the start later and the finish earlier, which shortens the window from both ends. Lean on the fastest types, harvest them at baby size, and keep fabric or a low tunnel over the bed through the whole season rather than only in spring. A south-facing bank or a spot against a wall gains a few days at each end.
To find the zone for your own community, use Natural Resources Canada’s Plant Hardiness Site. Look up your own municipality there instead of assuming Whitehorse applies. Then compare it with the Whitehorse figures above to judge how many weeks to add or subtract.
Where to check this for your own county
Yukon has no counties and no state extension service, so the nearest equivalent is federal and territorial agriculture offices. Start with Agriculture and Agri-Food Canada, which links to regional resources. The territorial agriculture branch and local gardening groups in your community are the closest sources for your own valley.
When you reach them, look for two things. The first is a planting calendar made for your area, with dates for cool-season crops such as brassicas and leafy greens. The second is a list of varieties trialled locally, since a variety that performs well in one community can fail in another a few hundred miles away.
A local recommendation beats a territorial one every time. The dates here describe the territory from one station’s long-term averages, and the 1981-2010 Canadian normals do not line up with the 1991-2020 US normals used for American calendars. If you borrow a calendar from the United States, expect the dates to be off.
Checking this against your own garden
Your own beds outrank every date above. Three observations cost nothing and tell you more than a regional average.
- Soil warmth by feel. Press your bare hand flat on the bed for a minute. If it still feels cold, seed will sit. A bed that feels cool but not cold earlier than your neighbor’s has good sun and drainage, so you can sow earlier there.
- First true leaves. After the two seed leaves, the first true leaves show how fast a bed is growing. If they appear promptly, the spot is warm. If they take much longer, the microclimate is cold and you should sow later or add cover.
- First frost marks. In late summer, note the first dark, wilted leaf on a tender plant such as potato foliage. If it comes before August 25, your site runs colder than the Whitehorse average and your window ends sooner.
Write the dates in a notebook. After two or three seasons, those notes will serve as a calendar more accurate than anything published.
Common questions
Can I start Asian greens indoors in Yukon?
Yes, a few weeks before setting out, but most of these greens are quick enough to sow directly under cover. Seedlings that get chilled after transplanting can bolt early, so harden them off and keep fabric nearby.
Can I sow a second crop in August?
Rarely. The average first frost is August 25, and growth slows quickly as days shorten. A covered bed might yield a few small leaves from a sowing in the last days of July, but the main harvest comes from sowings made by early July.
Do Asian greens survive frost?
Hardy types such as tatsoi and mizuna tolerate light frost, and the cold can improve their flavor. A hard freeze kills them. Cover the bed on nights when frost is forecast, especially in September.
How long until I can harvest?
Baby leaves of mizuna, tatsoi and komatsuna are often ready quickly. Full-size bok choy takes longer, so give it the earliest part of the window. Check the packet and count from sowing for direct-sown rows.