Sow hardy Asian greens such as bok choy, tatsoi, and mizuna outdoors in May, once the soil has thawed and drained, and make a second sowing in early July for a fall crop. At the Anchorage reference station, the last spring frost falls between May 3 and May 12, and the first fall frost between September 22 and October 1. Those dates fit southcentral Alaska. Gardens farther north need a shifted calendar.
The short answer for Alaska
Spring sowing runs from the day the ground can be worked through the end of May. A fall sowing goes in around early July. The frost dates behind that advice come from NOAA’s 1991-2020 Climate Normals for the Anchorage station. They mark the band where the probability of a 32°F freeze sits between 30 and 70 percent. A freeze can still show up after the later date in some years, so treat the window as odds you are playing.
The reference station has about 143 frost-free days between the mean last spring frost (May 3 to May 12) and the mean first fall frost (September 22 to October 1). That is a short season, and Anchorage is one of the mildest inhabited parts of the state. Long summer daylight makes up for part of the shortfall, because plants photosynthesize for most of the day in June and July.
When do you sow Asian greens outdoors in spring in Alaska?
Bok choy, tatsoi, mizuna, and komatsuna shrug off light frost, so they do not need to wait for the last frost date to pass. What they need is soil that has thawed, drained, and crumbles in your hand. In the Anchorage area the May 3 to May 12 band is a good target for the main sowing. Earlier than that, sow only under a low tunnel, in a cold frame, or in a greenhouse.
Sowing too early has its own cost. Young plants that sit through weeks of cold and then meet very long days are the ones that send up flower stalks. A small sowing every two weeks through May and into early June spreads that risk and keeps cuttings coming.
When do you sow for a fall crop?
Early July is the usual starting point. Take the days to maturity on the seed packet (counted from sowing for direct-sown greens), add a week or two because growth slows as the days shorten, and make sure the total ends before the first fall frost window opens on September 22. Fall plantings often taste better than spring ones. Shortening days hold off bolting, and cool nights sweeten the leaves.
| Sowing | Window (Anchorage reference) | What to know |
|---|---|---|
| Indoor-started transplants | About a month before the May window | Harden off before setting out; handle roots gently |
| Direct sowing, spring | When soil is workable, through May | Hardy types take light frost; cover on hard-freeze nights |
| Repeat sowings of cutting greens | Every two weeks into early June | Spreads the harvest and the bolting risk |
| Fall crop | Early July | Count packet days plus a week or two before September 22 |
Which kinds to choose for each window is covered in The Best Asian Greens for Alaska.
What will not work here
Which Asian greens are too slow for the season?
Heading napa cabbage and large daikon radishes need a long stretch of steady cool growth. Sown in June, napa meets the longest days of the year and tends to flower before it forms a tight head. Sown after mid-July, it runs into the September 22 to October 1 frost band with a half-grown plant. Both do better when you pick a short-season variety and sow in the first window or the early July one. The fast cutting greens (mizuna, tatsoi, baby bok choy) fit the Alaska calendar far more comfortably.
Do Asian greens survive an Alaska winter?
No. The mean daily minimum of the coldest month at the Anchorage reference station is 11.0°F, and the soil is frozen through winter. A late-September sowing meant to overwinter and sprout in spring will not come back. Light frost in fall is fine for the hardy types, and a good frost can improve flavor, but a deep freeze ends the crop. Treat every Asian green as an annual and harvest before the hard freeze.
Why do heat-loving greens struggle?
Water spinach and other warm-climate greens want warm nights and warm soil. Alaska summers deliver long days but cool nights, and the soil never gets the sustained warmth those plants expect. Outdoors, they stay small and yellow. If you want to grow one, it belongs in a greenhouse or high tunnel, where the air and soil heat up.
Root maggots cause a different kind of failure. Cabbage root maggot tunnels into radishes, turnips, and the roots of young brassicas, which includes bok choy and napa. A sheet of floating row cover laid over the bed at sowing, with the edges buried or weighted, keeps the egg-laying flies off. Putting the cover on after you see damage is too late.
Copying someone else’s dates is the last mistake worth naming. The 143 frost-free days belong to Anchorage. Fairbanks, the Interior, and the north have far shorter seasons, and a July sowing that works in Anchorage can be caught by frost before it is ready farther north.
What changes across Alaska
On the USDA Plant Hardiness Zone Map (2023, built on 1991-2020 normals), Alaska spans zones 1a to 8a. That is a gap of dozens of degrees in average annual extreme minimum temperature, from the Arctic slope to the southeast coast and the Aleutians. No single sowing date works across a spread like that. The Anchorage dates above are a reference point, and every other garden shifts from them.
The zone number tells you whether a perennial survives winter. For annual greens, frost dates and soil thaw matter more, since the plants only need to live from spring to fall. Still, the zone gives a rough idea of how far your site sits from the reference city. In the Interior, spring comes later and fall frost arrives sooner, so the whole calendar narrows from both ends. At altitude, the same shift applies, and cold air pooling in a valley can add an extra frost or two.
A gardener in the north should lean on the fast cutting greens, start transplants indoors so that the short outdoor season is spent growing, and use row cover or a low tunnel at both ends of the season. Coastal gardens in the southeast and along the Gulf are milder in winter but cooler and wetter in summer, so drainage and spacing matter more there than frost.
To find your own zone, use the USDA Plant Hardiness Zone Map and enter your ZIP code. Do not guess from a neighbor’s town. Zones can change over a few miles in Alaska’s mountains and valleys.
Where to check this for your own county
The University of Alaska Fairbanks Cooperative Extension Service is the place to confirm any date in this article. Look first for the local planting calendar for your area, which will give spring and fall dates that match your climate better than a statewide window. Then look for the vegetable varieties that have been trialled near you. A variety that performs well in Palmer is not guaranteed to do the same in Fairbanks or Juneau, and trial results show which ones bolt late and finish before frost.
Alaska is organized into boroughs, not counties, and extension offices serve districts, so search by your community or call the nearest district office. Extension staff can also tell you about local pest pressure, such as root maggot timing, and about soil tests that fit your site.
A local recommendation beats a state one every time. What you have read here is the state-level view, anchored to one reference station and meant to get you into the right month. Extension agents and experienced neighbors know your elevation, your wind, and your soil, and their dates should override anything printed here when they disagree.
Checking this against your own garden
Your own observations outrank every date above. Three of them are worth watching each spring and fall, and they tell you more about your microclimate than a calendar can.
- Soil warmth by feel. Dig down a few inches and squeeze a handful. If it crumbles and does not feel icy or soggy in your palm, it is ready for hardy greens. Cold, clumpy soil means wait. A south-facing slope or raised bed will pass this test days or weeks ahead of a shaded, low spot.
- Bud break on birch and willow. When the local birches begin to leaf out, the ground around them has usually warmed enough for the first sowing. Compare that date from year to year and you will learn how your site runs relative to the Anchorage dates.
- First true leaves. After the two seed leaves, the first true leaves should appear within a reasonable time. If they are slow, the soil is cold or the bed is shaded. Later, a center that starts to lengthen is the first sign of bolting, which tells you the season for that planting is ending.
Write down the dates you sow and the dates these signs show up. After two seasons, you will have a calendar tuned to your own ground. For the wider picture of crops and seasons, see Growing Asian Greens in Alaska.
Common questions
Can you start Asian greens indoors in Alaska?
Yes, and it helps in short-season areas. Bok choy and napa transplants started indoors gain weeks of growth. Harden them off for several days before planting, and handle the roots gently, since these greens dislike disturbance.
Is it too late to sow Asian greens in August?
For most types in the ground, yes, because the first fall frost at the Anchorage reference station arrives between September 22 and October 1. Fast baby-leaf greens like mizuna and tatsoi may still give small cuttings, especially under row cover or in a greenhouse. Farther north, the deadline comes earlier.
Will frost kill Asian greens?
Light frost does not harm hardy types such as bok choy, tatsoi, and mizuna, and it can sweeten the leaves. A hard freeze will damage or kill them, so cover plants on forecast nights and finish the harvest before deep cold sets in. Nothing survives an Alaska winter outdoors, where the mean daily minimum of the coldest month at the Anchorage station is 11.0°F.
Do long summer days make Asian greens bolt?
Long days are one trigger, along with early cold stress and warm spells. Bok choy and napa are the most likely to flower early. Choosing bolt-resistant varieties, sowing early in the window or in early July, and picking leaves young all reduce the problem.