Wisconsin gives Asian greens two sowing windows. The first opens in mid-April, when the soil can be worked, and closes before summer heat sends the plants to seed. The second opens in late July and runs through early September, timed for a harvest before the first hard freeze in mid to late October. Midsummer is the dead zone.
The short answer for Wisconsin
Sow Asian greens outdoors from about April 16 into May for a spring crop, and from late July through early September for a fall crop. Fall is the better bet, since shortening days and cool nights suit these plants while spring plantings race against rising heat.
The anchor dates come from the NOAA 1991-2020 Climate Normals. The last spring frost falls between April 16 and April 29, and the first fall frost between October 17 and October 29. Both ranges are the 30% to 70% band of probability for a 32°F freeze. Around April 16, the odds of another freeze still sit near 70%, and by April 29 they have dropped to about 30%. In fall the odds run the other way: roughly 30% that a freeze has already hit by October 17, and 70% by October 29.
When do you sow Asian greens in spring in Wisconsin?
Mustard-family greens shrug off a light frost, so the first sowing can go in as soon as a handful of soil crumbles instead of smearing. In most years that means mid-April or soon after. Seedlings can take a night at 32°F, but a harder freeze will damage them, so keep row cover handy until the frost band has passed. Sow again every week or two through mid-May. After that, lengthening days push most types toward flowering.
When do you sow Asian greens for fall in Wisconsin?
Count back from the October band using the days to maturity on the packet, which run from sowing for direct-seeded greens. Slow types such as Napa cabbage go in from late July to early August. Bok choy follows through August, and quick baby leaves such as mizuna and tatsoi can go in until early September. Varieties differ a lot in speed, so check The Best Asian Greens for Wisconsin before buying seed.
| Type | Spring sowing | Fall sowing |
|---|---|---|
| Baby leaves (mizuna, tatsoi, baby bok choy) | Mid-April to mid-May | Mid-August to early September |
| Full-size bok choy and similar | Late April to mid-May | August |
| Napa cabbage | Usually skipped (bolts) | Late July to early August |
What will not work here
Midsummer sowings fail. Seed put in from June through mid-July meets hot soil and the longest days of the year, and bok choy, mizuna and Napa respond by sending up flower stalks before the leaves reach a useful size. Spring brings its own pest, the flea beetle, which riddles young seedlings with tiny holes. A floating row cover laid over the bed at sowing keeps it off.
Weekly watering will not carry a late-summer sowing either. Seed sown in August lies in warm soil whose top inch dries out quickly, and shallow-rooted greens stop growing once the surface is dry. Light watering until the seedlings are up works far better. Close spacing causes trouble when late summers turn humid: Napa heads and bok choy packed tighter than the packet spacing hold moisture in the leaf, and rot follows.
Can you sow Napa cabbage in late August in Wisconsin?
No. Napa needs the longest runway of any common Asian green, and a late-August sowing runs into the October 17 to October 29 freeze band before the head fills. Inland southern Wisconsin typically freezes in early October, and the north far earlier, so the margin shrinks the farther you sit from Lake Michigan, which delays the first fall freeze at the lakeshore. Fast types still make it at that date. Slow ones do not.
Do Asian greens survive a Wisconsin winter outdoors?
Not in the open. The mean daily minimum of the coldest month is 17.2°F at Milwaukee, and since that is an average, plenty of nights run colder. Plants left standing in January are finished. A low tunnel or hoop house with row cover can carry hardier types such as tatsoi and mizuna well into early winter, which makes for a nice bonus harvest but a poor basis for a plan.
What changes across Wisconsin
There is no single answer, because the state spans USDA hardiness zones 3b to 6a, six half-zone steps between the far north and the southeast. That system rests on one variable, the average annual extreme minimum temperature, so it measures winter cold rather than the length of the growing season. For annual greens, frost dates matter more, but the zone spread shows how far apart two Wisconsin gardens can sit.
The frost dates above come from a single reference station, and the 17.2°F coldest-month minimum is Milwaukee’s. Gardeners in the northern counties should move both windows inward. Spring sowing starts later because the ground thaws later, and fall sowing starts earlier because the first freeze arrives far ahead of October 17. A modest shift at each end is a sensible first step. Napa cabbage may not finish at all up there, while quick baby leaves and bok choy are safer bets.
The lakeshore works the other way. Lake Michigan delays the first fall freeze, which buys extra weeks for fall plantings, though the cool water also slows spring warming. Inland southern gardens fall in between, with freezes that typically arrive in early October. To find your own zone, use the USDA Plant Hardiness Zone Map and enter your ZIP code. For the wider growing picture, see Growing Asian Greens in Wisconsin.
Where to check this for your own county
The University of Wisconsin-Madison Division of Extension runs an office in every county, and that is the best next stop. Look for two things there. The first is a local planting calendar for cool-season vegetables, which gives the spring and fall sowing dates your county’s staff actually use. The second is any variety trial results, meaning which bok choy, Napa or mizuna types were grown in your county and which bolted or rotted.
Extension calendars are usually written one crop at a time, so search for bok choy, Chinese cabbage or cool-season cabbage-family crops and read the one that matches what you are sowing. Local master gardener volunteers can also tell you which of the two frost bands has been running early or late in recent years.
A county recommendation beats a state one. A statewide timetable averages gardens from the Lake Michigan shore to the northern woods, and the spread in zones and freeze dates between them is wide. Treat the dates here as a starting range, then tighten them with the county’s own numbers.
Checking this against your own garden
Your own ground outranks every date above. Three things are worth watching, and none needs equipment.
- Soil warmth by feel. Squeeze a handful from a few inches down. If it crumbles and feels cool rather than cold after a minute in your palm, it is ready for spring seed. A south-facing bed beside a wall will pass this test days ahead of a shaded one, which shows how much your sunniest and coolest corners differ.
- The first true leaves. The first pair up are seed leaves. The next pair, shaped like the adult plant, are the true leaves. Sow a short test row and see how quickly they come. Slow, pale seedlings mean the bed is still too cold, and fast ones mean you can sow the main crop.
- The first frost damage. In fall, note when tender plants such as basil or squash blacken. Low spots and open yards freeze first, while beds near the house or a lake stay green longer. If your damage date lands well before October 17, move next year’s fall sowings earlier.
Write the dates in a notebook season after season. By the second year you will have a calendar that fits your lot better than any state average.
Common questions
Can you sow Asian greens before the last frost in Wisconsin?
Yes, within limits. Seedlings handle a light frost, and sowing from mid-April makes sense once the soil is workable. A hard freeze below 32°F can still damage them, so keep row cover on hand until the frost band of April 16 to April 29 has passed.
Is it too late to sow Asian greens in September?
Early September still works for fast baby leaves such as mizuna and tatsoi. Full-size bok choy and Napa will not finish before the October freeze band, so they belong in July and August.
How often should you sow in each window?
Small batches every week or two spread the harvest and cover you against a bad stretch of weather. A single big sowing tends to mature all at once, and then half of it bolts or gets frosted together.
Can you grow Asian greens through the summer?
Most types bolt under the long, hot days of June and July, even with shade cloth. Waiting until late July for fall sowings gives better results. Soil still warm from summer also makes for fast germination.