The best Asian greens for Wyoming are the fast, cool-loving types: mizuna, tatsoi, komatsuna, mustard greens and compact bok choy. They mature in weeks, take light frost in stride, and fit inside a late spring and an early fall. Large napa cabbage and slow Chinese broccoli types are the gamble. The reasons, and how to adjust for your elevation, follow below.
The short answer for Wyoming
Choose by type, then let the calendar confirm it. At the Cheyenne reference station, the last spring frost falls between May 7 and May 18, and the first fall frost between September 24 and October 5. Those dates come from NOAA’s 1991-2020 Climate Normals and mark the stretch where the chance of a 32°F freeze sits between 30% and 70%. The reference station has about 130 frost-free days between the mean last spring frost and the mean first fall frost, at roughly 6,000 feet. At higher elevations, frost can arrive in any month.
Which types fit a 130-day season?
A fast-maturing crop fits easily. A crop that needs a long season, with warm weather throughout, does not. Most leafy Asian greens are cut-and-come-again crops, so you can start harvesting baby leaves and keep going until a hard freeze.
| Type | Frost tolerance | Fit for a short, cool season |
|---|---|---|
| Mizuna | High | Excellent; fast, sown spring and late summer |
| Tatsoi | High | Excellent; low rosette stays tidy in wind |
| Komatsuna | High | Very good; forgiving of temperature swings |
| Mustard greens | Moderate to high | Very good; bolt quickly once days lengthen |
| Compact bok choy | Moderate | Good, best sown in late summer for fall |
| Choy sum | Moderate | Fair; needs a protected, early start |
| Napa cabbage, Chinese broccoli (gai lan) | Moderate | Risky; long to mature, needs season extension |
Which crop should you sow first?
Start with mizuna, tatsoi and mustards under row cover in spring. Save bok choy and any napa for a late summer sowing, so they mature in the cooling days of September. Exact sowing windows are laid out in When to Sow Asian Greens in Wyoming.
What will not work here
Slow, heading crops sown in spring fail first. A napa cabbage started in May needs a long stretch of mild weather to form a tight head. Instead it meets lengthening days and heat, and it sends up a flower stalk before the head fills. Bok choy sown in spring does the same thing, which is why a spring planting is better treated as baby leaf than as full-size heads.
Sowing on the average last frost date also fails. With May 7 to May 18 marking a 30% to 70% chance of a 32°F freeze, a freeze after those dates is still a real possibility. Cold soil slows germination, and seedlings that sit in it stay small. Row cover or a low tunnel at sowing protects against both.
Leaving plants uncovered through winter does not work either. The mean daily minimum of the coldest month at the reference station is 18.1°F. That is an average, so many nights run colder. Even the hardiest greens will not hold up in an open bed through a stretch like that. Treat all of them as annuals, and consider a cold frame only if you want a few extra weeks of leaves in late fall.
Watering is the next trap. Dry air and steady wind pull moisture from the top few inches of soil fast, and shallow-rooted greens suffer first. Stressed plants turn bitter, tough and quick to bolt. A thin mulch and short, frequent watering in the first weeks keep the leaves tender.
Wind and hail round out the list. Tall, floppy leaves like those of large bok choy tear in a gusty afternoon, and a single hailstorm can strip a bed. Low rosette types such as tatsoi take the abuse better, and a hoop frame with row cover doubles as hail insurance.
Finally, close spacing is less risky here than in humid states, since dry air limits fungal problems. Crowding still hurts, though. Plants packed tight compete for water, and in a dry spell that competition shows up as early bolting.
What changes across Wyoming
Wyoming has no single answer. The USDA Plant Hardiness Zone Map (2023, based on 1991-2020 normals) places the state in zones 3a to 6a. That system rests on one variable, the average annual extreme minimum temperature, so it tells you about winter lows and nothing about growing-season length. Still, the spread is wide, and it signals how different a garden in a low basin can be from one in the mountains.
The dates and day counts above describe the Cheyenne reference station, near 6,000 feet. Gardens elsewhere will differ, and at higher elevations frost can arrive in any month. If you garden in the north or at altitude, shift everything toward the cold side. Sow spring crops later, since soil takes longer to warm. Start fall crops earlier, since the first hard freeze comes sooner. Lean even harder on the quick types in the table, and treat a low tunnel as standard equipment rather than an extra.
Low basins and warmer valleys may offer a longer season, but cold air pools in low spots on clear nights, so frost can still arrive early. A garden on a slope often escapes it. Wind exposure varies as well. A bed beside a fence or the south wall of a house can run noticeably warmer than an open lot nearby.
To find your own zone, use the USDA map and enter your ZIP code, rather than guessing from the state range. For a broader overview of the crop group, see Growing Asian Greens in Wyoming.
Where to check this for your own county
A county recommendation beats a state one. Statewide guidance gives a sensible starting point, but a county office knows its own frost pockets, its elevation band and the soils people actually garden in. University of Wyoming Extension runs local offices, and that is the place to ask.
Two things are worth looking for. First, a planting calendar for your county or the nearest town at a similar elevation. A calendar built on local frost dates is more reliable than one built on a distant station. Second, any varieties trialled nearby. Cultivars differ widely in bolt resistance and cold tolerance, and local trial results show which mizuna, mustard or bok choy performed well in similar conditions.
Ask the office a few specific questions as well. When does the soil typically become workable in your area? How often do late freezes come after the average last frost date? Does wind or hail commonly damage spring crops where you live? Local gardeners and Master Gardener volunteers usually know these answers from years of experience, and their answers are often more precise than any published average.
If the office has no leafy Asian greens guidance, ask about the closest relatives, such as kale, spinach, arugula and radish, which like the same cool conditions. A calendar for those crops is a good stand-in.
Checking this against your own garden
Your own observations outrank every date in this article. Three are worth watching.
The first is soil warmth by feel. Press your bare hand flat into the bed in the morning. If the soil feels cold and clammy, seeds will sit and wait, so hold off or cover the bed for a week. A bed that feels cool but not cold, as if the ground has stopped holding winter, is ready. If one corner warms sooner than the rest, that is your early spot.
The second is the first true leaves. After the two seed leaves, the first pair of true leaves shows the plant has settled in. If that takes noticeably longer than the packet suggests, your bed runs cold or windy, and you should leave the cover on longer or sow later next year.
The third is the first frost on the grass. When you see white on the lawn, walk to the garden and check which plants are frosted and which are not. Spots that frost first are your cold pockets, and spots that stay clear are your best places for fall bok choy. Keep notes, and your own records will beat any published average.
Common questions
Can you grow bok choy in Wyoming?
Yes, with the right timing. Sow compact types in late summer so they mature in cool September weather. Spring sowings tend to bolt as days lengthen, so use them as baby leaf.
What is the easiest Asian green to start with?
Mizuna and tatsoi are the most forgiving. Both grow fast, tolerate frost and handle wind better than large-leaved types.
Do Asian greens survive winter outdoors?
Not in an open bed. The coldest month averages a daily minimum of 18.1°F at the Cheyenne reference station, which is too cold for exposed plants. Treat them as annuals.
Do you need row cover for Asian greens in Wyoming?
For most gardens, yes. About 130 frost-free days leave little margin, and frost can arrive in any month at higher elevations. Row cover or a low tunnel protects early sowings and extends the fall harvest.