The best Asian greens for Idaho are the fast, cold-tolerant leaf types: mizuna, tatsoi, komatsuna, mustard greens and baby bok choy. Sow them in spring and again in late summer, and skip anything that needs a long, steady season. The frost dates below come from Boise, a low valley. Most of the state is higher, colder and shorter-seasoned, so treat the Boise figures as a ceiling.
The short answer for Idaho
Asian greens are cool-season crops, and Idaho’s cool seasons are short. In Boise, the last spring frost falls between April 23 and May 7, and the first fall frost between October 7 and October 21. Both ranges come from NOAA’s 1991-2020 Climate Normals for the Boise station, and both are probabilities. Each marks the stretch where the chance of a 32°F freeze sits in a 30-70% band. Neither is a promise that the cold is over or has arrived.
That framing matters because the gap between those dates is only part of the story. Most Asian greens perform best on either side of midsummer, in spring before the heat and in fall as it fades. A crop that finishes quickly slips into those shoulders easily. One that needs a long run does not, which is why the choice comes down to type rather than cultivar.
| Type | Spring sowing | Late-summer sowing | Verdict for Idaho |
|---|---|---|---|
| Mizuna, tatsoi, komatsuna, mustard greens | Strong | Strong | First choice anywhere in the state |
| Baby or small bok choy | Good, bolts if heat arrives early | Very good | Reliable if harvested young |
| Choy sum, gai lan, full-size bok choy | Risky | Good in low valleys | Needs a longer cool stretch |
| Napa cabbage and other heading types | Poor | Possible in low valleys only | Skip at altitude |
Exact sowing dates depend on your own frost window, and the page on When to Sow Asian Greens in Idaho works through them. For the wider picture of crops, soil and care, start with Growing Asian Greens in Idaho.
What will not work here
Start with the spring trap. April 23 looks like a green light, but at the early end of that band a 32°F freeze is still a live possibility. Seedlings of the hardy leaf greens shrug off a light frost. Tender seedlings of larger types do not, and a long cold spell followed by lengthening days can push young plants to bolt early. A strip of row cover costs little. Replanting a bed in May costs more.
Heading types are the next casualty. Napa cabbage and full-size choy sum want weeks of mild weather to fill out. Sown in spring, they hit midsummer heat before they are ready and run to seed. Sown in late summer in a low valley like Boise, they have a fair shot before the October 7 to October 21 frost window. Higher up, where fall frost comes earlier, they simply run out of calendar.
Winter is not on the table either. The mean daily minimum of the coldest month in Boise is 25.4°F. That is an average, so many nights are colder, and Boise is among the mildest places in the state. Unprotected Asian greens will not produce through an Idaho winter in the open. Some hardy types survive under cover and resume growth in early spring, but that is a bonus, not a plan.
Then there is water. Southern Idaho valleys are dry in summer, and shallow-rooted greens that dry out between weekly soakings turn bitter, stall or bolt. This page’s facts do not include rainfall or summer highs, so read that as general regional knowledge rather than a measured figure. The practical point holds anyway: a bed of fast greens needs even moisture, which usually means short, frequent watering and a mulch.
Tropical Asian greens such as water spinach want sustained heat and a long season. Idaho offers neither in any reliable way, so leave them to warmer states.
What changes across Idaho
Idaho does not have one garden. The USDA Plant Hardiness Zone Map (2023 edition, built on 1991-2020 normals) places the state anywhere from zone 3b to 7b. That is a wide spread, and no single recommendation covers it. A gardener in a low southwestern valley and one in a high northern or mountain town are working with different calendars, different risks and, for the most part, different crops.
Keep in mind what that zone number measures: one variable, the average annual extreme minimum temperature. It tells you whether a perennial survives winter. For annual greens that live a few weeks, season length and summer heat matter more, and the zone says little about either. Use it as a rough guide to how cold your area runs, not as a planting date.
If you garden in the north or at altitude, shift three things from the Boise reference. Move spring sowing later and fall sowing earlier, since both frost dates compress the season. Lean harder on the quickest types, which means the leaf greens and baby bok choy in the table above. And plan on row cover or low tunnels to stretch both ends, because every extra week counts when the window is short. Heading cabbages are the first thing to drop from the list.
To find where you fall, check the USDA Plant Hardiness Zone Map and look up your location directly. Do not assume a neighbor’s zone is yours: hills, valleys and lakes can change the picture within a few miles.
Where to check this for your own county
The best next stop is University of Idaho Extension, the state’s land-grant extension service. Its county offices know the local frost pockets, soils and water, which a state-level page cannot.
When you get there, look for two things. First, a local planting calendar for your county, or the nearest one that matches your elevation. Second, any vegetable varieties trialled in your county or a similar one, including cool-season brassicas and leafy greens. A trial result from a similar elevation is worth more than any general variety list, including this one.
This page does not list an Idaho-specific extension calendar for Asian greens, so I won’t point you to one that I haven’t verified. If your county office has nothing on Asian greens by name, ask about bolting dates for lettuce, spinach or cabbage-family crops. Those are close relatives and a good proxy.
A county recommendation beats a state one, plainly. This page is the state one: a reference built on Boise’s numbers and a general understanding of how these crops behave. Use it to narrow your choices, then let your county’s advice overrule it wherever the two disagree.
Checking this against your own garden
Your own observations outrank every date on this page. Three are worth watching, and none needs equipment.
First, soil warmth by feel. In spring, push your hand into the bed an inch or two deep. If it feels cold and clammy, seeds will sit and may rot. If it feels merely cool and crumbly, you are in good shape for hardy greens. Compare spots: a south-facing bed beside a wall will warm up sooner than a shaded corner, and the difference is your microclimate.
Second, the first male flowers on squash or zucchini, if you grow them. Those blooms show up once the garden has really warmed. When you see them, spring sowing of Asian greens is nearly over, and it is time to plan the late-summer round. Note the date in a notebook for a few years and you will have your own local calendar.
Third, the first true leaves. After the seed leaves open, the first real leaves tell you how fast the seedlings are growing. Quick, healthy true leaves mean the bed suits the crop. Slow, pale ones suggest cold soil, shade or dryness. Thin once they appear, and check again in a week: a bed that lags behind the rest of your garden is telling you something about its position.
Common questions
Can I grow bok choy in Idaho?
Yes, especially small or baby types. Harvest them young, sow in spring and again in late summer, and keep them evenly watered. Full-size plants are riskier because they bolt in heat.
Which Asian greens handle cold best?
Mizuna, tatsoi, komatsuna and mustard greens are the hardiest of the group and the safest bet across the state. Under row cover, some will keep going later into fall than other types.
Is napa cabbage worth trying in Idaho?
Only as a fall crop in a low valley like Boise, where the first fall frost arrives between October 7 and October 21. At higher elevations, the season is too short for it to head up reliably.
Can I grow Asian greens through an Idaho winter?
Not reliably in the open. Boise’s coldest-month mean daily minimum is 25.4°F, and colder parts of the state are harsher. A tunnel or cold frame can carry hardy types further, but plan on a pause.