Sow Asian greens in Illinois twice: in early spring as soon as the soil can be worked, and again from late August into mid-September for a fall crop. The fall sowing is usually the better bet. Every date here is anchored to the Chicago reference station, so a suburban or rural garden may run a week or two behind. For the wider picture, start with Growing Asian Greens in Illinois.
The short answer for Illinois
Plan on a spring window from late March to mid-April and a fall window from the last days of August to mid-September. Both are counted from frost dates, and those dates are probabilities, not promises.
The figures come from the NOAA NCEI 1991-2020 Climate Normals. They give a last spring frost of April 11 to April 22 and a first fall frost of October 24 to November 3. Each range is the band where the chance of a 32F freeze sits between 30 and 70 percent. In any given year the freeze can land on either side of it.
| Sowing | Window (Chicago reference) | How it is counted |
|---|---|---|
| Spring | Late March to mid-April | As soon as soil is workable, ahead of the April 11 to April 22 last-frost band |
| Fall | Last days of August to mid-September | Rule of thumb: count back six to eight weeks from the October 24 to November 3 band |
Why spring starts before the last frost
Bok choy, tatsoi and mizuna are cool-season crops. Seedlings shrug off a light frost, so waiting for April 22 to pass wastes the best weeks. The real deadline is the other end: as days lengthen and warm up, spring plantings run to seed (bolt) early, so a sowing in late April or May often gives you flower stalks instead of tender leaves.
Why fall is the easier season
Sown as summer fades, the plants grow into shortening, cooling days, which discourages bolting. Fall sowing also tends to bring less insect pressure than spring, and the leaves sweeten after a few light frosts. Count back from the frost band and add a buffer, because a garden outside the city will likely see its first freeze earlier than the airport does. Which types to sow when is covered in The Best Asian Greens for Illinois.
What will not work here
Sowing in July for a fall crop is the classic miss. Soil that hot keeps many cool-season seeds from germinating well, and the seedlings that do come up face a heat-stressed start, then flea beetles, then bolting. The August-to-September window exists precisely to skip that stretch.
Slow, head-forming types are the next casualty. Napa cabbage and large-headed Chinese cabbage need a long run of cool weather to fill out. With a first fall frost between October 24 and November 3, a sowing in early October has no chance of finishing, and even a mid-September sowing is tight. Fast, loose-leaf types leave far more margin.
Winter is the third wall. The mean daily minimum of the coldest month is 18.8F, and that is an average, so plenty of January nights go colder. Tougher greens like tatsoi and mizuna take a hard frost in stride, but an average night in the high teens is more than most Asian greens survive uncovered. A cold frame or row cover can stretch the season, yet planning on open-ground overwintering sets you up for a bare bed in March.
Illinois summers are also humid, which punishes crowded plantings. Tight spacing in a wet spell holds moisture on the leaves and invites rot and mildew. Give bok choy heads room to breathe, and thin seedlings early instead of letting them jostle.
One more trap is treating the airport numbers as your own. The CAUTION attached to the frost data is plain: suburban and rural gardens typically see the last spring frost later and the first fall frost earlier than the reference city, often by one to two weeks, and more at elevation. If you shift both ends of the Chicago window that way, the spring window narrows and the fall deadline arrives sooner. A gardener who sows on the Chicago dates in a cold-pocket rural lot is gambling with the margin already spent.
What changes across Illinois
Illinois does not have one planting date. The USDA Plant Hardiness Zone Map (2023 edition, built on 1991-2020 normals) places the state anywhere from zone 5a to 7b. That is a spread of several half-zone steps from the northern border to the southern tip, so there is no single answer to give a statewide gardener.
Keep in mind what the zone measures. It rests on one variable, the average annual extreme minimum temperature, so it tells you about winter survival. It says nothing directly about your last spring frost, your first fall frost or how hot July gets. Two gardens in the same zone can still have different sowing calendars.
The practical shift runs in a predictable direction. In the colder northern part of the state, expect a later spring start and an earlier fall cutoff than the Chicago figures, so lean on fall sowing and keep spring plantings small and early. In the milder south, the frost dates should come later in fall, which gives fall crops more room, though the hotter summer makes the late-August start a matter of watering seedlings through lingering heat. Treat all of that as direction, not as a dated recommendation: this page has the reference-city figures only.
To see where your own garden falls, look up your location on the USDA Plant Hardiness Zone Map and read the zone for your ZIP code yourself. This page will not guess it for you, and neither should a neighbor two counties over.
Where to check this for your own county
Your state extension service is the next stop. University of Illinois Extension runs county-level offices staffed by horticulture educators and Master Gardeners who know local conditions, such as which low spots hold frost and which soils warm slowly.
Look for two things when you get there. The first is a local planting calendar for your county, with frost dates and sowing windows for cool-season vegetables. The second is any record of varieties trialled in your area, because a bok choy that holds up in one county’s heat can bolt in another’s.
Be plain with yourself about the hierarchy. A county recommendation beats a state one, and this page is the state one. It is built on a single reference station, and it does not contain a county calendar, so I will not pretend it does. If extension and this page disagree, go with extension, then adjust for your own yard.
If you cannot find a calendar that names Asian greens specifically, a cool-season vegetable calendar for cabbage, kale or spinach is a reasonable proxy. Those crops share the same preference for cool soil and short days, and the sowing dates transfer well enough to give you a starting point.
Checking this against your own garden
Dates are a starting guess. What the garden itself tells you outranks them, and three signals cost nothing to watch.
- Soil warmth by feel. In spring, push your hand into the bed. If it still feels cold and clammy and clumps in a tight ball, wait. Cold, soggy soil rots seed. A bed that crumbles and feels merely cool is ready, and it tells you your site thaws early or late compared with the neighbors.
- First true leaves. After the seed-leaves, the first real leaves show how fast seedlings are moving. Slow, pale growth in a fall sowing means you started too late for that spot. Reach them by mid-October, and you can count on a crop.
- Where frost lingers. On the first frosty mornings, note which parts of the yard are white and which are green. The low corner that stays white is your cold pocket, and it will hit its last and first frosts on the wrong side of the reference dates.
Write down what you see for a season or two. A simple note on the calendar, with the date you sowed and the date you first saw true leaves, will be worth more than any regional table.
Common questions
Can I sow Asian greens in Illinois in July?
You can, but results are poor. Hot soil hurts germination, seedlings fight heat and flea beetles, and plants bolt readily. Waiting until the last days of August gives the same fall crop with far less struggle.
Do I have to wait until after the last frost in spring?
No. The Chicago reference range is April 11 to April 22, but spring sowings start once the soil can be worked, since seedlings handle a light frost. Cover them if a hard freeze is forecast.
Will Asian greens survive an Illinois winter outdoors?
Mostly not. The mean daily minimum of the coldest month is 18.8F at the reference station, and many nights run colder. Hardy types may limp through under a cold frame or row cover, but open-bed survival is unreliable.
Do these dates work for southern or northern Illinois?
Only as a starting point. The dates come from the Chicago reference station, and the state spans hardiness zones 5a to 7b. Check your county with University of Illinois Extension and shift for your own garden, as outlined above.