Asian greens go in twice in New Hampshire: a quick spring sowing once the soil has dried and warmed, and a main sowing in late summer for fall. At the reference airport station, the last spring frost falls between April 16 and April 27, and the soil warms after that. Spring crops race against lengthening days. Fall crops finish in cooling weather, which suits the family far better. The basics are covered in Growing Asian Greens: Fast, Cold-Hardy, and Prone to Bolting.
When the soil is warm enough in New Hampshire
The date most gardeners want is the last spring frost. NOAA’s 1991-2020 U.S. Climate Normals put it between April 16 and April 27 at the airport reference station, using the 32 F freeze probabilities in the 30 to 70 percent band. Those are odds drawn from three decades of records, so a given year can land on either side of them.
Why does the frost date come before the planting date?
A frost date describes the air. Asian greens respond to the soil, and the soil is still shedding winter cold when the last freeze passes. Seed sown into cold, wet ground sits and rots, or comes up slowly and stalls. Cold snaps followed by lengthening days also push young plants to bolt before they form a usable head or rosette. Wait for the soil to follow the air, usually a week or two past the frost window.
That gap matters more for a garden away from the airport. Suburban and rural plots typically see the last spring frost one to two weeks later than the reference station, and hilltop or higher-elevation sites run later still. New Hampshire spans USDA hardiness zones 3b to 6a on the 2023 map, so a garden in the North Country and one near the southern border are not on the same calendar. Check the frost history for your own county before you mark a date.
How do you tell the soil is ready?
Squeeze a handful from 3 or 4 inches down. If it crumbles instead of forming a wet ball, it is workable. Then push a soil thermometer about 2 inches deep at mid-morning, and watch it over several days. A reading that climbs and stays up beats any single warm afternoon. Raised beds and south-facing slopes get there first, and a sheet of clear plastic laid over the bed for a few days ahead of sowing speeds things up.
Lay row cover over the seedlings after sowing. It adds a few degrees on cold nights and keeps flea beetles off the first leaves, which is a bigger problem for this family than most beginners expect. For the types that suit a short spring run, see the last section below.
How long the season lasts here
The reference station has about 170 to 190 frost-free days between the mean last spring frost (April 16 to April 27) and the mean first fall frost (October 13 to October 26). That is a comfortable stretch for a cool-season crop, but most of it is the wrong weather for these plants. Lengthening days and warm nights from late spring through midsummer push them to flower. The usable windows sit at either end of the season.
What does that window allow?
It allows two sowings, and the second one matters most. A first sowing of quick types in spring gives you greens before summer heat arrives. A second sowing in late summer matures as days shorten and nights cool, and the plants sweeten in cold weather instead of bolting. Counting back from the first fall frost tells you the last workable sowing date for each type. Use the days-to-maturity figure on your seed packet, counted from sowing for direct-seeded crops, and add a margin for the slower growth of short autumn days.
Further sowings in between are worth trying only in the cooler parts of the state or in shade. The succession sowing guide on this site lays out how to space them so you are not harvesting everything in the same week.
Should you transplant or sow direct?
Where the season is long enough for a second sowing, direct seeding is simpler and avoids root disturbance. Transplanting is worth it when you want a head start on napa cabbage or bok choy in spring. Check the roots before planting: seedlings that have circled the pot or sat too long in a tray tend to bolt early once they are in the ground. A root check at the nursery counter or in your own tray saves a lot of disappointment. Gardeners in colder places with much shorter seasons can compare notes in Growing Asian Greens in Alaska, and those with similar cold winters but a different pattern of rain and heat can read Growing Asian Greens in Wisconsin.
Heat and water in New Hampshire
New Hampshire summers are mild compared with the Mid-Atlantic or the South. Hot spells above 90 F happen at the reference station, but they arrive in short runs and are not the defining feature of the season. A hot-climate plan built around shade cloth and afternoon relief is rarely needed here. Mulch and a little afternoon shade on the hottest days will do.
Summer rain is regular, and humid air lingers in valleys and near water. What a cool, damp summer brings is trouble of a different kind: mildew on the leaves, slow growth, and soft rots at the base of heads that stay wet. Space plants for airflow, water at the soil line in the morning, and avoid overhead sprinklers late in the day. Leaf spots and downy mildew spread fastest in crowded beds with wet foliage overnight.
What do the first frost and the winter low decide?
This family belongs to the second half of the year, so the numbers that govern it come later in the calendar. The mean first fall frost is October 13 to October 26 at the reference station, and again gardens inland and at elevation usually see it one to two weeks earlier. That date sets how late a sowing can still finish. A sowing that has not reached harvest size by then will mostly stand still through November, so count back with a margin.
The winter low decides the rest. The mean daily minimum of the coldest month is 17.1 F at the Manchester reference station, and that is an average, so individual nights run colder. Most Asian greens do not live through a New Hampshire winter uncovered. The hardiest leafy types, such as mustards, mizuna and tatsoi, can stand through hard frosts and often taste better for them. Under a low tunnel or heavy row cover, some keep going into early winter. Against 17.1 F averages, plan to harvest before the real cold arrives and treat any winter survival as a bonus.
Which Asian greens suit New Hampshire
Choose by type. The season is short enough that early-maturing types suit the spring sowing, the mild summer makes disease resistance the first thing to look for on a seed packet, and cold nights in fall reward the hardy leafy greens. Compact heads and loose rosettes handle damp weather better than tight, heavy ones.
| Type | Why it fits | What to watch |
|---|---|---|
| Small bok choy and tatsoi | Compact and quick, good for a spring sowing and again in fall | Bolts in warm spells and long days |
| Mizuna and komatsuna | Leafy, cool-tolerant, and reliable for the fall sowing | Flea beetles on young leaves |
| Leaf mustards | Take light frost, flavor turns sharp in heat | Bolting in warm weather |
| Napa cabbage | A fall crop that rewards an early-August start | Rot in wet, tight heads |
Every one of these is a brassica, and so are turnips and rutabagas. They share pests and diseases with cabbage, kale and mustard, including flea beetles, cabbage worms and clubroot. A bed that grew any of them last year should not take these greens this year. Moving them into a cabbage bed rotates nothing, so rotate to a different plant family.
Which varieties should you buy?
Buy the ones trialled where you live. A variety that does well in a southern New Hampshire river valley can fail in the White Mountains, and the only reliable guide is local trial results. University of New Hampshire Extension and your county office can point you to what has been tried in your zone. Skip the cultivar names printed on seed racks until you have checked them against that advice, because disease resistance and bolting tolerance differ a lot between packets sold under similar names.
At harvest, inspect each head or root before storing it. A soft patch, a weeping spot or a moldy crown ends the question, and the plant goes in the compost, not the fridge.
Common questions
When can I sow bok choy outside in New Hampshire?
Sow once the soil is workable and warming, usually a week or two after the last frost at your site. The airport reference station’s April 16 to April 27 window is the earliest you should think about it, and most gardens come later.
Can Asian greens survive a New Hampshire winter?
The hardiest types may stand through early winter under a tunnel or heavy cover. With the coldest month averaging a daily low of 17.1 F at Manchester, most will not carry on uncovered.
Do turnips and rutabagas count in crop rotation with Asian greens?
Yes. They are brassicas, like cabbage, kale and mustard, and they share diseases and pests. Keep all of them out of a bed for a few seasons before planting the family there again.
Where can I find the best varieties for my county?
Ask your county office or University of New Hampshire Extension. Their trial results reflect your own elevation, frost dates and soil, which no general list can.