Sow Asian greens outdoors in Oklahoma from late February to early April for a spring crop, and again from late August through September for a fall crop. Fall is the more forgiving season, because soil cools slowly and the first freeze arrives late. Spring sowings have a short runway before heat pushes the plants to bolt. The dates below come from the Oklahoma City reference station, so shift them for your own ground.
The short answer for Oklahoma
Sow cool-season Asian greens from late February to early April, then again from late August through September. At the Oklahoma City reference station, the last spring frost falls between March 28 and April 10, and the first fall frost between October 29 and November 8.
Those dates come from the NOAA 1991-2020 U.S. Climate Normals for the airport weather station. They are probabilities of a 32°F freeze. Inside each band, the odds of a freeze run between 30 and 70 percent. Before the spring band opens, a freeze is likely. After it closes, a freeze is unlikely but still possible. Suburban and rural gardens usually see the last spring frost later and the first fall frost earlier than the airport, often by one to two weeks, and more at elevation.
Mizuna, tatsoi, komatsuna, mustard greens and bok choy shrug off light frost as seedlings. That is why the spring window is timed to the last-frost band rather than after it. Here is how the main types line up:
| Type | Spring sowing | Fall sowing |
|---|---|---|
| Baby leaf (mizuna, tatsoi, komatsuna) | Late February to early April | Late August to early October |
| Mustard greens | Late February to mid-March | September |
| Bok choy, full heads | March, early | Late August to mid-September |
| Napa cabbage | Poor odds; skip | Late August to early September |
How soon can you harvest?
Count from the day the seed goes in the ground. For a closer look at which types suit which season, see The Best Asian Greens for Oklahoma.
What will not work here
A hot, dry summer ends most Asian greens. Sow after mid-April and the plants hit summer heat before they size up. Bok choy, tatsoi and mizuna then send up flower stalks and turn bitter within days. Spring sowing works only when the crop is nearly done by the time nights stay warm.
Which sowings fail most often?
- Napa cabbage in spring. It needs a long stretch of cool weather to form a head. Oklahoma spring jumps from freezes to heat too quickly, so it bolts before it heads.
- Late fall heading types. With the first fall frost band running October 29 to November 8 at the reference city (earlier for many rural gardens), napa sown in October cannot finish.
- Midsummer sowing. Seed sown in July or early August germinates poorly in hot soil. Seedlings that do come up need daily moisture.
- Weekly watering. Shallow-rooted greens dry out fast in wind and heat. A weekly soaking leaves them stressed and bitter between waterings.
Winter is gentler than many gardeners expect. The mean daily minimum of the coldest month at the reference station is 27.0°F. Hardy leaf types often survive that under a row cover. Heading types will not, and any plant caught by a hard freeze after a warm spell can be lost overnight. For a broader look at the crop, Growing Asian Greens in Oklahoma covers soil and care.
Red clay soil adds another snag. It crusts after rain, and tiny Asian green seeds struggle to push through. A thin layer of compost over the row keeps the surface loose.
What changes across Oklahoma
Oklahoma spans USDA hardiness zones 6a to 8a. That zone system rests on a single number, the average annual extreme minimum temperature, so it says nothing about heat, wind or rainfall. A range this wide means there is no single sowing date for the whole state. The reference city sits in the middle of the spread, and gardeners in the far northwest or the southeast will both be off from its dates.
How should northern and high-elevation gardeners shift?
Where winters are colder, in the panhandle, the northwest and the higher ground, the last spring frost comes later and the first fall frost comes earlier. Plan on pushing the spring start back by one to two weeks and the fall sowing earlier by the same margin. A shorter season also makes fall the better bet, since the spring window closes quickly once heat arrives.
Southern gardens and those near the Red River sit in the warmer zones. Spring can start a bit sooner there, but the heat arrives sooner too, so spring crops need an earlier finish. Fall sowing may wait a bit longer, because soil stays warm well into September.
The USDA Plant Hardiness Zone Map shows where a given ZIP code falls. Look yours up there rather than guessing from the state average. Zone matters most for winter survival, and the frost dates matter most for sowing.
Where to check this for your own county
A county recommendation beats a state one, and this is the state-level view. Oklahoma State University Extension runs county offices across the state, and their staff know the local frost dates and soil.
When you reach the extension site, look for these things:
- A local planting calendar for cool-season vegetables, with spring and fall dates for your county.
- Variety trials run in your county or a similar one, which show which Asian greens held up through heat and cold.
- Frost date guidance for the nearest town, which will be closer to your ground than airport data.
County agents can also tell you about local pest pressure, such as flea beetles in spring, and about soil testing. If your county office has a master gardener program, those volunteers often field exactly this question each season.
Checking this against your own garden
Your own observation outranks every date above. Three things are worth watching, and none needs equipment.
- Soil warmth by feel. Push your hand a few inches into the bed in the morning. If it feels cold enough to numb your fingers, seed will sit. If it feels cool and slightly damp, greens will sprout. A bed against a south wall warms days before a low, shaded one.
- Redbud bloom and tree leaf-out. When the redbuds flower and maples start to leaf, the worst freezes have usually passed locally. Late bloom in your yard means a colder microclimate than the reference city.
- First true leaves. After the two seed leaves, the first true leaves show whether seedlings are growing or stalling. If they come slowly, the bed is colder than you assumed, and the next sowing can wait or go under cover.
Low spots where cold air pools often freeze later than the rest of the yard, so a note on where frost lingers each morning is worth keeping from year to year.
Common questions
Can I sow Asian greens in Oklahoma before the last frost?
Yes. Mizuna, tatsoi, komatsuna, mustard and bok choy seedlings tolerate light frost. Sowing from late February is common, and a row cover helps if a hard freeze threatens after the seeds sprout.
What is the best month for fall sowing?
September suits most types. Napa cabbage and full-size bok choy do better when sown in late August to early September, so they have time to size up before the first fall frost, which reaches the reference city between October 29 and November 8.
Why do my Asian greens bolt so fast in spring?
Warm days and lengthening daylight trigger flowering. Sowing too late, or sowing types that need a long cool season, sends them to seed before they size up. Earlier sowing and bolt-resistant varieties help.
Do Asian greens survive Oklahoma winters?
Hardy leaf types often do. The coldest month’s mean daily minimum at the reference station is 27.0°F, which many greens tolerate under a row cover. Heading types such as napa cabbage generally do not survive a hard freeze.