Sow Asian greens in Utah from late March into April in the valleys, then again from late July through early September for fall. Spring seed has to mature before the heat of summer pushes the plants to bolt. Fall seed has to finish before the first hard freeze, which reaches Salt Lake City between October 18 and October 29. Higher and colder ground shifts both windows later in spring and earlier in fall.
The short answer for Utah
The dates behind that calendar come from NOAA’s 1991-2020 Climate Normals for the Salt Lake City station. They are probabilities of a 32°F freeze. In spring, the chance that a freeze is still to come sits between 30 and 70 percent from April 12 to April 29. In fall, the same 30 to 70 percent band for the first freeze runs from October 18 to October 29. Inside those spans it is close to a coin flip whether the next cold night brings ice.
That coin flip matters less for Asian greens than for tomatoes or squash. Bok choy, tatsoi, mizuna, komatsuna and the mustards are cool-season brassicas. Seedlings generally shrug off a light frost, and the seed germinates in cool soil. The enemy is heat and long days, so the calendar is built backward from summer as much as forward from frost.
When do you sow Asian greens in spring in Utah?
Start as soon as the soil can be worked without turning to mud, usually late March into April in the valley, ahead of the April 12 to April 29 frost span. Sow thinly every ten days or so for three or four rounds. Each round is harvested before the next summer heat wave arrives. After about the middle of May, spring sowings begin to race toward flowering, and the later rounds are better used as baby leaves than as full heads.
When do you sow Asian greens in fall in Utah?
Fall is the better season in most Utah gardens. Seed sown from late July through mid-August has time to make full-size bok choy and napa-type cabbage before the October 18 to October 29 freeze band. Fast leaf crops such as mizuna, tatsoi and baby bok choy can go in until early September. Seedlings sown in the heat of late July need shade cloth and steady moisture for the first two weeks, but the plants then grow into cooling weather, which is what they want.
| Type | Spring sowing (valley) | Fall sowing (valley) |
|---|---|---|
| Fast leaf crops: mizuna, tatsoi, baby bok choy, komatsuna | Late March through April, repeated every 10 days | Early August to early September |
| Full-size bok choy and Chinese cabbage | Late March to mid-April only | Late July to mid-August |
| Mustard greens | Late March to late April | August to early September |
For variety choices that fit these windows, see The Best Asian Greens for Utah. The wider overview is at Growing Asian Greens in Utah.
What will not work here
Salt Lake City has a hard frost on both ends of the season and a dry summer in between. That rules out several common habits.
Why do late spring sowings fail in Utah?
Seed sown in late May or June meets rising heat and the longest days of the year. Asian greens read that as a signal to flower, so they send up seed stalks while the leaves are still small. A bok choy sown in mid-June is often bitter and woody before it makes a usable head.
Why does weekly watering fail?
Asian greens have shallow roots and a fast growth rate. A bed that gets one deep soak a week dries out between waterings in a Utah summer. The plants then swing between wet and dry, which makes the leaves tough and speeds bolting. In fall, seedlings sown in late July and August need the top inch of soil kept damp every day until they are up. Drip lines or a light daily watering with a mulch of straw or grass clippings work far better than a weekly sprinkler session.
Why do slow varieties fail?
Counting from sowing, large Chinese cabbages and some heading mustards need a long season to head up. A seed sown in mid-September never gets there, because the first freeze band begins October 18 and growth slows long before. Choose quick types for sowing after early August and treat anything slower as a mid-summer crop with a firm deadline.
Will Asian greens overwinter outdoors?
Rarely, and not in the open. The mean daily minimum of the coldest month at the reference station is 24.2°F, an average, so many nights run colder. Most Asian greens are damaged by hard frost, and some kinds stand more cold than others. Without a row cover, low tunnel or cold frame, a December bed is usually finished. Fall plantings are for harvest in October and November, not for surviving to spring.
What changes across Utah
Salt Lake City sits in a mild valley. Most of Utah is higher and colder, and southern Utah is warmer. The USDA Plant Hardiness Zone Map (2023, built on the 1991-2020 normals) places the state between zones 4a and 9a. A hardiness zone measures only the average annual extreme minimum temperature, so it describes winter survival and says little about the length of the season. Even so, the spread tells you there is no single sowing date for the state.
Gardeners in the northern mountains, high valleys and benchlands should expect a later spring start and an earlier fall deadline than the Salt Lake dates. The first round slides from April toward May, and you should count back from the first hard freeze to decide the last day to sow. Row cover is the main tool here, since a sheet of floating fabric can extend the season at each end. Quick leaf crops are safer than heading types.
Gardeners in the warmer south, including the St. George area, reverse the problem. Spring is short because heat arrives early, so the first sowing may go in early. The fall sowing is pushed later, into September or even October, because summer stays hot much longer. For these gardens, fall and winter may be the best Asian greens season of the year, with some plants surviving mild winters outdoors under light cover.
Where to check this for your own county
Your county office of Utah State University Extension can give you more precise dates than any statewide calendar. Extension staff know the elevation, the frost pockets and the water situation in your part of the state. They also see what actually grows locally, year after year, and what failed.
When you contact the county office or browse its gardening resources, look for two things:
- A local vegetable planting calendar that lists spring and fall dates for cool-season crops such as bok choy, Chinese cabbage and mustard greens.
- Any list of varieties trialled or recommended in your county, especially for bolting resistance in spring and cold tolerance in fall.
Ask also about local frost dates. Many counties publish their own, and a gap between a valley floor and a nearby bench is ordinary. Where the county and the statewide calendar disagree, trust the county, then confirm it against what your own beds do.
Checking this against your own garden
Dates are averages and gardens are not. Two things you can see or feel will tell you more than any calendar.
Soil warmth by feel. Push your hand a few inches into the bed in early spring. If the soil is workable, crumbles in your fist and no longer feels icy, seed will germinate. If it clumps into a cold, wet ball, wait a week. Beds on south-facing slopes and near walls reach this point days or even weeks ahead of low, shaded ground, and that gap is your own microclimate.
The first true leaves. Sow a short test row at the start of the window. Seedlings first show two rounded seed leaves, then the first true leaves with the shape of the mature plant. If true leaves appear promptly and the plants stay compact, the timing is working. Quick stretching and early flower buds mean your site runs warmer or the sowing came too late.
Keep a notebook with the date you sowed, the date seedlings came up and the date the first plants bolted. After two seasons, your own record will outrank every date printed anywhere else.
Common questions
Can I sow Asian greens in Utah in summer?
From late July onward, yes, for fall harvest. Sowing in June is a poor bet because heat and long days push the plants to bolt. Keep the bed shaded and damp until the seedlings are up, then let the cooling weather do the work.
How late can I sow bok choy in Utah?
For full-size heads in the valley, aim for late July to mid-August. Baby bok choy and other fast leaf crops can go in as late as early September if you have row cover for the October nights. In colder, higher areas, count back from your own first freeze.
Do Asian greens survive frost?
Light frost is usually fine for seedlings and mature plants, and it often sweetens the leaves. Harder freezes, with nights in the mid-20s or lower, damage most types. Mizuna and tatsoi take the cold best, and a cover of fabric buys extra weeks.
Why do my Asian greens bolt in Utah?
Heat and long days trigger flowering, which is why spring sowings made after about mid-May and anything sown in June struggle. Uneven watering, crowded plants and dry soil add stress. Sow earlier in spring, shift your main crop to fall, and keep the soil evenly moist.