Asian greens get two sowing windows in New Hampshire: spring, from mid-April into mid-May, and late summer, from late July into early September. Midsummer is a dead zone for most types. Gardens inland, in the north, or at elevation should start spring sowings a week or two later and finish fall sowings a week or two earlier.
The short answer for New Hampshire
Sow hardy leaf types such as mizuna, tatsoi and komatsuna outdoors from mid-April as soon as the soil is workable. Sow bok choy and napa cabbage mainly for fall, starting in late July. Those dates rest on frost records from Manchester, so they are a starting point for a reference city. They are not a promise for every town in the state.
NOAA’s 1991-2020 climate normals put the last spring 32°F freeze between April 16 and April 27. The first fall freeze lands between October 13 and October 26. Both ranges are the 30 to 70 percent probability band. On the spring dates, the chance of another freeze falls from 70 to 30 percent. On the fall dates, the chance that a freeze has already arrived climbs through the same band.
Those figures come from the airport weather station. Suburban and rural gardens usually see the last spring frost later and the first fall frost earlier, often by one to two weeks, and more at elevation. For a wider view of the crop group, see Growing Asian Greens in New Hampshire.
When do you sow Asian greens in spring?
Start at the front of the spring band, not after it. The hardy leaf types shrug off light frost, and the seed germinates in cool soil. The reason to hurry is the calendar ahead: as days lengthen and warm up, the plants shift from making leaves to making flower stalks. A sowing that goes in during mid-April has weeks of cool growth. One that goes in during June has almost none.
When should you sow Asian greens for fall?
Count backward from the first fall freeze. Heading types such as napa cabbage need a long season from sowing, so they go in during late July or early August. Bok choy follows in early to mid-August. Leaf types like mizuna and tatsoi take less time and tolerate cold well, so they can be sown into early September. Check the days on your seed packet and subtract them from the freeze dates above, then pull the result earlier if your garden sits inland or on a hill.
| Type | Spring sowing | Fall sowing |
|---|---|---|
| Mizuna, tatsoi, komatsuna | Mid-April to mid-May | Mid-August to early September |
| Bok choy | Late April to mid-May | Early to mid-August |
| Napa cabbage | Usually skipped (bolts) | Late July to early August |
What will not work here
Can you sow Asian greens in June and July?
Mostly no. Bok choy and napa cabbage sown near the summer solstice meet the longest days of the year and warm nights, and they bolt before they form anything worth harvesting. A row of napa sown in mid-June is a common way to grow tall yellow flower stalks. Leaf types hold on a bit longer but turn bitter and tough. Use the gap to prepare the fall bed instead.
Why do late sowings fall short?
The season closes sooner than most seed packets assume. Napa cabbage sown in late August has well under 60 days before the first fall freeze, which arrives October 13 to 26 at the reference station and earlier inland. The result is a loose, small head that never fills. The slowest heading types simply do not fit a late start. If you missed early August, switch to mizuna, tatsoi or baby-leaf bok choy, which can be cut young. The best Asian greens for New Hampshire are the ones that finish inside this window.
Will Asian greens survive a New Hampshire winter outdoors?
Not in open beds. The mean daily minimum of the coldest month at Manchester is 17.1°F, and the state’s hardiness zones, in the USDA system, run from 3b to 6a. Most Asian greens give up long before that. Hardy leaf types can last into December under row cover or in a cold frame, but plan on harvest ending when the ground freezes unless you build protection. Do not count on a January salad from a bare bed.
What goes wrong with early spring sowings?
Two things. Seed sown into cold, soggy April soil can sit for weeks and rot before it sprouts, so wait until the soil crumbles in your hand instead of smearing. Flea beetles also arrive as soon as spring brassicas are up and riddle the leaves with tiny holes. A light row cover laid over the bed at sowing keeps them off, and it also gives a few degrees of frost protection.
What changes across New Hampshire
New Hampshire spans USDA hardiness zones 3b to 6a (USDA Plant Hardiness Zone Map, 2023, built on 1991-2020 data). That is several full zones, so there is no single answer for the state. The cold end sits in the north and the mountains. The mild end lies toward the southeast and the coast. A gardener in the North Country and one near Portsmouth are working with different seasons.
The zone only describes the average annual extreme minimum temperature. It says how cold the worst winter nights get. It says little about when the last frost ends or when the first one starts, and those dates are what govern Asian greens. Two gardens in the same zone can differ by a week or more in the date they can first sow.
For a rule of thumb, take the dates above and shift them. Add one to two weeks to the spring start in suburban and rural gardens. Pull fall sowings one to two weeks earlier. At elevation or in a cold hollow, push that further: heading types may need sowing in mid-July, and spring sowing can wait until early May.
Colder gardens also benefit from fast varieties. A bok choy bred to mature quickly is a safer bet than one that needs a long season. Do not assume your zone from memory or from a neighbor’s garden. Look up your own location on the USDA Plant Hardiness Zone Map, then use the shift above to adjust the dates.
Where to check this for your own county
A county recommendation beats a state one, and the dates above are the state-level version, anchored to a single reference city. Frost, snowmelt and summer heat vary enough between the Seacoast, the Merrimack Valley, the Lakes Region and the North Country that a local source will correct them.
University of New Hampshire Extension is the place to go. Once there, look for three things:
- A vegetable planting calendar for your county or region, with spring and fall sowing dates for cool-season crops.
- Any list of varieties trialled in New Hampshire, especially for bok choy, napa cabbage and the leaf types.
- Local frost dates, and pest alerts for flea beetles and other brassica problems.
If the county office offers a soil test, take it up. A fall bed that drains badly or sits acidic will hold back greens no matter how well the sowing date is chosen. When a county calendar and the dates in this article disagree, follow the county.
Checking this against your own garden
Your own observations outrank every date here, because they record what your plot actually does. Three are worth watching.
Soil warmth by feel. In spring, grab a handful of soil from the bed. If it holds together in a cold, wet clump, wait. If it crumbles and feels cool but not clammy, seed will germinate. A bed that reaches that point a week before the neighbor’s is a warm spot and can be sown first.
The first true leaves. Seed leaves come up first. The first true leaves appear after, and they show how the plants are doing. If a spring sowing makes true leaves quickly and stays compact, the timing is right. If it jumps up thin and starts to stretch a stalk, your garden warms faster than the calendar suggests, so sow earlier next year.
The first frost on the lawn. On the first white morning of fall, walk the yard. Frost that coats the low corner but spares the bed beside the house maps your cold pockets. Sow fall greens in the protected spots, and move tender types to where the frost came last.
Common questions
Can I sow Asian greens before the last spring frost?
Yes, for the hardy types. Mizuna, tatsoi and komatsuna tolerate light frost, so sowing in mid-April is reasonable once the soil is workable. Cover the bed with row cover if a hard freeze is forecast. Bok choy tolerates cold less well, so wait until late April.
Is September too late to sow Asian greens?
Early September still works for fast leaf types, especially with row cover. After that, growth slows as days shorten and nights drop. A sowing in mid-September may only give you tiny seedlings before frost, so treat it as a cold-frame project.
Why does my bok choy bolt in spring?
Bok choy flowers when days lengthen and warm up, and a cold snap when the plants are small can push it that way too. Sow it early in the spring window or, better, in early August for a fall crop, when days are shortening instead of lengthening.
Should I start Asian greens indoors?
Direct sowing works well and is simpler, since seed packet days count from sowing. Starting transplants indoors ahead of time can get a jump on spring, but chilled seedlings may bolt after planting out. Harden them off gradually and plant them in a protected spot.