The Best Asian Greens for most Illinois gardens are the quick, cool-tolerant types: bok choy, tatsoi, mizuna, komatsu na and mustard greens, sown in spring and again in late summer. Slow or heat-loving types, such as full-size napa cabbage in spring or water spinach anywhere, are the risky picks. Frost dates, a cold winter low and a wide hardiness spread explain why. For the bigger picture, see Growing Asian Greens in Illinois.
The short answer for Illinois
Choose by type, not by seed-packet name. Fast leaf greens (baby bok choy, tatsoi, mizuna, komatsu na, mustards) fit Illinois best, because they finish in the cool weeks bracketing summer. Medium-speed types such as choy sum and full-size bok choy work in both spring and fall. Napa cabbage is a fall crop here, not a spring one.
The frost dates show why. At the Chicago-area reference station, the last spring frost falls between April 11 and April 22, and the first fall frost between October 24 and November 3. Those figures come from the NOAA NCEI 1991-2020 Climate Normals and describe the 30-70% band of probability for a 32°F freeze. They are odds, not promises. A freeze can still arrive after the later date, and it may hold off past the earlier one.
They also describe an airport, not your yard. 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. Treat the dates as a starting point and check your county (more on that below).
| Type | Speed | Cold tolerance | Heat tolerance | Best Illinois window |
|---|---|---|---|---|
| Tatsoi, mizuna, komatsu na | Fast | High | Low to moderate | Early spring and fall |
| Baby bok choy | Fast | Moderate | Low | Spring and fall |
| Mustard greens | Fast to medium | High | Low | Spring and fall |
| Choy sum, full-size bok choy | Medium | Moderate | Low | Spring and fall |
| Napa cabbage | Slow | Moderate | Low | Fall |
This page has no summer temperature or rainfall figures for Illinois, so it leans on frost dates and winter lows. For exact sowing dates, When to Sow Asian Greens in Illinois takes up where this leaves off.
What will not work here
Start with the slowest crops. Full-size napa cabbage sown in early spring has to head up before summer warmth arrives, and the gap between a mid-April last frost and the first hot stretch is short. The plants often bolt instead. The same cabbage sown in late summer and harvested before the October 24 to November 3 frost window has the cool weather it wants.
Heat-lovers fail for the opposite reason. Water spinach and other tropical greens want warm nights and a long, steady season. In Illinois they can be started after the last frost, but a cold snap in spring or an early fall freeze ends them. Their window is narrower than the frost dates suggest, because suburban and rural gardens often lose one to two weeks at each end compared with the airport figures.
Winter is not a gentle edge
The mean daily minimum of the coldest month is 18.8°F at the Chicago reference station. That is an average, so colder nights are normal. Hardy types such as tatsoi, mizuna and mustards shrug off light frost and even a hard freeze for a while, but an unprotected bed will not carry bok choy through a typical Illinois January. Plan on row cover, a cold frame or a low tunnel if you want winter harvests, and treat anything that survives in the open as a bonus.
Summer humidity punishes close spacing
Midwest summers tend to be humid, and Asian greens are leafy, tender and packed tight. Crowded rows hold moisture on the leaves, which invites fungal disease and slugs. A fall crop sown in August faces that humidity as a seedling, so give plants room and water at the soil, not over the leaves. Weekly deep watering is also a poor fit for baby greens, which have shallow roots and stall if the top inch dries out.
What changes across Illinois
Illinois is not one garden. The state spans USDA hardiness zones 5a to 7b, a range built on a single variable: the average annual extreme minimum temperature. Each half-zone is a 5°F step, so six steps separate the coldest northern pockets from the mildest spots in the far south. No single answer fits the whole state.
The frost dates and the 18.8°F figure on this page belong to the reference city in the north. A gardener in the northern counties should lean toward the reference dates, or later in spring and earlier in fall once suburban and rural effects are counted. That means starting cool-season crops a little later in spring, finishing fall sowings sooner, and relying more on row cover. Hardy leaf types are the safest bet.
Farther south, spring generally warms earlier and the first fall frost arrives later, which widens both windows. The trade-off is that summer heat comes sooner, so spring crops have less time before bolting. This page does not carry frost dates for southern Illinois, so it cannot give you numbers there. Look up your own area rather than borrowing the northern dates.
Elevation and local terrain matter too. Low spots collect cold air and frost earlier. A bed against a south wall can run noticeably warmer than one in the open. To see where your own county falls, use the USDA Plant Hardiness Zone Map and look up your location rather than guessing from a neighbor.
Where to check this for your own county
A county recommendation beats a state one. This page is the state one: a reference-city set of frost dates, one winter low and a broad hardiness range. Local advice accounts for your county’s soils, frost pockets and the varieties that have actually been grown there.
Your best source is University of Illinois Extension, the state’s land-grant extension service. Go there and look for two things. First, a local planting calendar or vegetable guide for your county or region, which gives sowing windows tuned to your area instead of the airport. Second, any variety trial results for leafy and Asian greens, so you can see which bok choy, mustard or napa types did well nearby and which bolted.
If the site has no Asian-greens calendar for your area, use its general cool-season vegetable dates, which govern crops like cabbage, kale and lettuce. Asian greens follow the same rhythm. Your county extension office can also answer questions by phone or email, and local Master Gardener volunteers often know which spots in town frost first.
One caution: calendars from other states are tied to their own climates and crops, so skip them. Use the Illinois source for your county, and treat this page as the backdrop it fits into.
Checking this against your own garden
Dates on a page are averages. Your garden’s own signals outrank every one of them, and three are easy to read without any equipment.
- Soil warmth by feel. Dig a handful in early spring. If it crumbles instead of clumping into a cold, wet ball, and feels cool but not icy in your palm, cool-season greens can go in. Cold, soggy soil rots seed. Compare a sunny bed with a shaded one: the difference tells you which spot to sow first.
- First true leaves. After the seed leaves, the first true leaves show how the seedling is coping. Steady growth means conditions suit it. Stalled, purplish or leggy seedlings point to cold nights or too little light in that spot.
- The first male flowers on squash. If you grow squash, its early male blooms mark the arrival of dependable warmth in your yard. When they appear, spring greens are close to bolting and it is time to plan the late-summer sowing.
Write down the dates you see each year. After two or three seasons, your notes will tell you more about your microclimate than any airport station.
Common questions
What is the easiest Asian green to grow in Illinois?
Mizuna, tatsoi and komatsu na are the most forgiving. They grow fast, take cool weather and light frost, and can be harvested as baby leaves long before heat or hard freezes arrive.
Can I grow napa cabbage in Illinois?
Yes, as a fall crop. Sown in late summer, it heads up in cooling weather before the first fall frost window of October 24 to November 3 at the reference city. Spring sowings often bolt.
Do Asian greens survive an Illinois winter?
The hardiest types may, with protection. The coldest month’s mean daily minimum is 18.8°F at the Chicago reference station, so use row cover or a cold frame and expect losses, especially in the colder northern zones.
Do the frost dates here apply to my yard?
Treat them as the reference-city figures only. Suburban and rural gardens often see the last spring frost one to two weeks later and the first fall frost one to two weeks earlier. Check with your county extension office.