Vermont gardeners get two chances at Asian greens: a spring sowing once the soil has warmed, and a late-summer sowing that matures in the cool of fall. The second usually does better. Bok choy, mizuna, tatsoi and mustard greens grow fast and shrug off light frost, but long spring days push them to bolt. Timing comes down to soil temperature in spring and the first hard freeze in fall.
When the soil is warm enough in Vermont
For Burlington, the NOAA 1991-2020 Climate Normals (station USW00014742) put the last spring 32°F freeze between April 30 and May 10, in the 30-70% probability band. Some years frost arrives later than that, so treat the window as odds. Burlington sits on Lake Champlain, the mildest corner of the state. The Green Mountains and the Northeast Kingdom run substantially shorter, and a garden up there should expect later dates and lean on a neighbor’s records or the extension office.
Why does soil temperature matter more than the frost date?
A frost date tells you when the air stops dipping to 32°F. The soil follows later. Vermont ground holds winter cold and snowmelt for weeks, and it warms only after the frost risk has ended. Sow on the frost date and the seed sits in cold, wet soil, where germination is patchy and some seed rots. Transplants set into that soil stall.
Cold has a second effect on this crop. A long chill early in a young plant’s life can trigger early flowering in some types, bok choy and napa especially. A spring sowing that gets chilled after it sprouts may bolt before it makes a usable plant.
How do you check that the soil is ready?
Push a probe thermometer to seed depth in the morning, when the soil is at its coolest. Take readings over several days in a row. One warm afternoon proves nothing. Compare the steady reading with the minimum on the seed packet for that type.
Soil that crumbles in your hand is also a good sign. A handful that smears or forms a wet ribbon is too wet to sow, whatever the thermometer says. Raised beds drain and warm sooner than flat ground, and clear or black plastic laid over a bed for a week or so before sowing gives the soil a head start. Row cover over the sown bed does the same job and also keeps flea beetles off the seedlings.
Asian greens come in many types, and the varieties that have been trialled in Vermont soils are the ones worth buying. University of Vermont Extension can point you to them for your county.
How long the season lasts here
The Burlington reference station has a last spring frost window of April 30 to May 10 and a first fall frost window of October 3 to October 13. Mountain and Northeast Kingdom gardens get less, and a frost pocket in a valley bottom loses days at both ends.
What that length allows matters more than the number. At the lakeshore, five months is enough for a spring sowing of the quickest types and then a second, larger sowing in late summer. Spring plants race the lengthening days toward bolting, so the second sowing is the one to count on. Work backward from the first fall frost window to pick the sowing date. Check whether the packet counts days from sowing or from transplanting, and add a margin, because growth slows as days shorten and nights cool in September and October.
Where the season is shorter, the first sowing may be the only one, and the choice between direct sowing and transplanting changes. Transplants buy a few weeks, but only if the roots are sound. Slide a seedling out of its cell before you buy or plant it. Roots should be white, loose and reaching the edges of the soil. A tight, circling mass means the plant has been stressed in the cell, and bok choy and napa that start out stressed tend to bolt. If the transplants are root-bound, direct sowing is the better bet.
Succession sowing, a small batch every week or two across the window, spreads the harvest and protects against a single bad week of weather. The Growing Asian Greens: Fast, Cold-Hardy, and Prone to Bolting guide covers the method in detail. Gardeners in other northern states work with similar windows, and the notes on Growing Asian Greens in Minnesota and Growing Asian Greens in Michigan show how the same plan shifts with a few weeks of difference.
Heat and water in Vermont
Summer heat is a small problem here compared with the South or the Plains. Hot spells do occur at Burlington, but they come in short runs and the hills stay cooler. Asian greens are cool-season crops, and the main heat concern is the midsummer sowing for fall. Soil in July can be hot enough to slow germination, so sow in the evening, water the row, and shade the bed with a light cloth or the shadow of taller plants until seedlings are up.
Water works the same way. Vermont gets regular summer rain, so drought is a lesser worry than too much moisture. A cool, damp summer brings downy mildew, leaf spots and slow growth, and plants that ripen slowly stay exposed to those diseases longer. Space plants to the wider end of the recommended range so air moves through the bed. Water at the base in the morning so leaves dry quickly, and avoid overhead watering late in the day. Row cover keeps flea beetles and cabbage moths off, though it needs lifting or sealing well at the edges to stop trapping humidity.
Every plant in this family is a brassica, and so are turnip and rutabaga. They share their diseases and pests with cabbage, kale and mustard, including clubroot and black rot. A bed that held any of them last year is a bad home for Asian greens this year. Rotating a turnip crop into a cabbage bed has rotated nothing. Keep the whole family out of a bed and follow a rotation plan that groups them together.
What does the first frost mean for a fall crop?
At Burlington the first 32°F freeze lands between October 3 and October 13, in the same 30-70% band. That date sets how late a sowing can still finish. A light frost sweetens many Asian greens and does them no harm. A hard freeze ends tender types such as full-size bok choy and napa heads. Sow late enough to avoid summer heat and early enough that plants are near full size when the frost window opens.
The winter low decides what happens after that. The mean daily minimum of the coldest month at Burlington is 12.9°F. It is an average of the nightly lows, so some nights fall well below it. The USDA 2023 Plant Hardiness Zone Map puts Vermont in zones 3b to 5b, built on the average annual extreme minimum, and the mountains sit at the colder end. At those temperatures, uncovered Asian greens do not stand through winter. Under a low tunnel or a cold frame, the hardiest types hold on for a while and then stop growing, and a cover only helps if it keeps the worst nights off the plants. Winter harvest is a bonus, not a plan.
If you harvest heads for storage, inspect each one before it goes in and again as it sits. A soft patch, a weeping spot or a moldy crown ends the question, and that head should be eaten at once or discarded.
Which Asian greens suit Vermont
Start with the clock. Vermont’s window is short in the hills and moderate at the lakeshore, so the earliest types come first. Baby bok choy, tatsoi, mizuna and leaf mustards harvested young finish fast, tolerate light frost, and can be cut at several sizes if a freeze comes early. Full-size bok choy and napa cabbage need more time and more protection, and in the mountains they are a gamble.
| Type | Speed | Cold tolerance | Fit for Vermont |
|---|---|---|---|
| Baby bok choy, tatsoi | Fastest | Good in light frost | Reliable at lakeshore and in the hills |
| Mizuna, leaf mustards | Quick | Among the hardiest | Good for late sowings and cover |
| Full-size bok choy | Moderate | Light frost only | Needs an early fall start |
| Napa cabbage | Slowest | Light frost; heads need protection | Best at the lakeshore, risky in the mountains |
Humidity changes the second question. Cool, damp summers favor mildew and leaf spots, so disease resistance is the first thing to read on the packet, ahead of flavor or leaf color. Choose resistance to the diseases that trouble brassicas, give plants room, and keep them out of beds where cabbage-family crops have grown recently. Where summer sowings face heat, a bit of afternoon shade at the roots helps them establish.
No variety names appear here on purpose. A variety that does well on the lakeshore can fail in the Northeast Kingdom, and only local trials show which ones hold up against Vermont’s frost dates, damp summers and soils. Ask University of Vermont Extension for the varieties trialled near you. Plant a small block of two or three types each year, keep notes on sowing and harvest dates, and let your own garden narrow the list.
Common questions
When can I plant bok choy outside in Vermont?
Wait until the soil has warmed and drained after the last frost window, which at Burlington runs April 30 to May 10. Spring plantings in cold soil tend to bolt, so many gardeners put their main sowing in late summer, timed to finish before the first fall frost window of October 3 to October 13.
Can Asian greens survive a Vermont winter?
Rarely. The coldest month at Burlington averages a nightly low of 12.9°F, and the hardiest types under a low tunnel or cold frame may hold on for a time. Most end with the first hard freeze, and uncovered plants will not stand through the winter.
Can I plant Asian greens where turnips or rutabagas grew?
No. Turnip and rutabaga are brassicas, and they share their pests and diseases with Asian greens, cabbage, kale and mustard. Rotate Asian greens away from every one of them.
Where do I find varieties that work in my part of Vermont?
Ask University of Vermont Extension. Conditions vary a great deal between the lakeshore, the Green Mountains and the Northeast Kingdom, and the varieties trialled locally are the most useful guide.