For most Maine gardens, The Best Asian Greens are the fast, cold-tolerant ones: tatsoi, mizuna, komatsuna, baby pak choi and the mustards. Sow them in early spring and again in late summer, and treat midsummer as a pause. Slow, heat-sensitive types like full-size napa cabbage are the gamble. The reason is a frost window that opens late and closes early.
The short answer for Maine
Choose by type. Quick leaf greens that mature in weeks are the dependable core of a Maine Asian greens bed, and long-season heading types are the ones that need luck. Two numbers decide this: when frost leaves and returns, and how cold the coldest month gets. The rest follows from them.
At the Portland reference station, NOAA’s 1991-2020 Climate Normals put the last spring 32°F freeze between April 22 and May 1, and the first fall freeze between October 9 and October 21. Those dates are not deadlines. Each marks the span where the probability of a 32°F freeze sits in a 30-70% band, so they describe odds that tilt from “likely” to “unlikely,” not a guarantee in either direction. Portland is also the mild end of the state, and the NOAA station data will not match an inland or northern garden.
The decision by type
Most Asian greens are cool-season crops. Hardy leaf types shrug off a light frost, so they can go in around the spring window instead of waiting for it to close, and they keep producing into the fall freeze. The table sorts the common groups by how well they match that short, cool season.
| Type | Examples | Fit for Maine | Best use |
|---|---|---|---|
| Fast leaf greens | Tatsoi, mizuna, komatsuna | Excellent | Spring and fall, repeat sowings |
| Baby or compact pak choi | Small bok choy types | Very good | Spring and fall, cut young |
| Mustards | Red and green leaf mustards | Very good | Cool weather, cut-and-come-again |
| Heading types | Napa cabbage | Risky | Midsummer sowing for a fall head |
| Tropical greens | Water spinach, Malabar spinach | Poor | Only with real warmth and protection |
Dates for each sowing are laid out in When to Sow Asian Greens in Maine. For the wider picture of the crop group, start with Growing Asian Greens in Maine.
What will not work here
Short seasons punish the slowest crops first. A full-size napa cabbage needs weeks of steady growth to form a tight head, and in Maine that clock runs into a fall freeze that can arrive as early as October 9 even on the coast. Start it late and you get a loose, unfinished head. Start it in spring and rising warmth and long days push it to bolt before it heads.
Tropical greens and winter plans
Water spinach and Malabar spinach are sold as Asian greens, but they are heat lovers. A 32°F freeze kills them, and the spring freeze odds do not settle until the end of the April 22 to May 1 band at the mildest site. Planting them out with the hardy greens is a bet against the thermometer. Gardeners who want them need a warm spot, a head start indoors and a plan for cold nights.
Outdoor overwintering is the second failure. The mean daily minimum of Portland’s coldest month is 15.6°F. That is an average, with colder nights inside it, and Portland is the mild end. Most Asian greens will not carry through a Maine winter in an open bed. A low tunnel or cold frame can stretch the harvest well into late fall, but planning on a January crop outdoors is optimistic.
The third trap is the single May sowing. A row of bok choy planted once and left alone meets a warm spell in early summer and sends up flower stalks, leaving bitter leaves. Even a mild-summer state has hot stretches, and that is enough to trigger bolting. Small successive sowings every couple of weeks, with a gap in midsummer and a restart in late summer, beat one big planting.
The last mistake is caution. Waiting until after the last frost for hardy greens throws away the cool weeks they like best. Seedling flea beetles are the real spring threat to mustards, mizuna and other brassicas, and a lightweight row cover handles them better than waiting does.
What changes across Maine
Maine is not one garden. The USDA Plant Hardiness Zone Map (2023, built on 1991-2020 normals) places the state across zones 3b to 6a. That is a spread of several half-zones, so there is no single answer. The frost dates above come from coastal Portland, and the caution attached to them is blunt: inland and northern Maine run substantially later in spring and earlier in fall.
Someone in the north or at elevation should shift in three ways. First, lean harder on the fastest types, such as tatsoi, mizuna and baby pak choi, and drop napa unless you are willing to cover it. Second, start the late-summer sowing earlier than a coastal calendar suggests, because the fall window closes sooner. Third, use row cover or a low tunnel at both ends of the season, since it adds protection when a short window has no slack.
Coastal gardens near the water sit at the mild end and have more room. Even so, a sheltered coastal yard and a frost pocket a few miles inland can behave quite differently, which is why the hardiness zone is only part of the story. It tracks the average annual extreme minimum temperature and nothing else. It says nothing about summer heat, and it does not tell you when frost arrives, which matters more for fast leaf crops.
To find which zone your property falls in, use the USDA Plant Hardiness Zone Map and look up your ZIP code. Do not rely on a neighbor’s guess or on a state average.
Where to check this for your own county
The best next stop is University of Maine Cooperative Extension, the state’s land-grant extension service. Look for two things there: a planting calendar for vegetables written for your region, and any information on which varieties have been trialled near you. Local trials tell you which cultivars held up through a real Maine summer and fall, which no national seed catalog can.
Ask your county office about local frost timing too. Its staff watch your area’s springs and falls and can tell you how your dates differ from a coastal reference.
A county recommendation beats a state one. This page is the state one. It is built on a single reference station, Portland, and a zone range from 3b to 6a, so it can say what generally works but not what works on your hillside. This page does not have a county-by-county Asian greens calendar, and it does not hold trial results for specific cultivars. When extension guidance and this page disagree, go with extension.
Checking this against your own garden
No date on this page outranks what your own bed is doing. Three observations will tell you more about your microclimate than any table.
Soil warmth by feel. In early spring, push your hand into the bed. If the soil is cold and clammy and clings to your skin, wait. If it crumbles and feels cool rather than icy, hardy greens can go in. A bed that reaches this state a week ahead of the rest of the yard is probably a sheltered, sunny spot, the place for your first sowing.
The first true leaves. Seedlings first show two rounded seed leaves, and the first true leaves follow. Note how long that takes after sowing, and compare beds. Fast, even growth means the spot suits the crop. Slow growth in one bed points to shade, cold soil or a cold air pocket.
Where frost blackens leaves first. In fall, notice which plants in your yard blacken first, and when. If they fall in the October 9 to October 21 window, you are close to the coastal reference. If they go earlier, move your late-summer sowing earlier and plan for covers.
Write the dates down for a season or two. Your own notes become a calendar no state page can match.
Common questions
What is the easiest Asian green to start with in Maine?
Tatsoi, mizuna and komatsuna are good first choices. They grow quickly, handle cool weather and can be cut young, which suits a short season.
Can I grow bok choy in Maine?
Yes, especially compact and baby types in spring and fall. Summer heat tends to push bok choy to bolt, so avoid sowing it to mature in midsummer.
Should I wait until after the last frost to plant?
Not for hardy greens. The April 22 to May 1 range is the band where a 32°F freeze has a 30-70% probability at Portland, and tatsoi, mizuna and mustards tolerate light frost. Tender types such as water spinach should wait until the freeze risk has passed.
Can Asian greens survive winter outdoors in Maine?
Mostly no. Portland’s coldest-month mean daily minimum is 15.6°F, and inland Maine is colder. With a cold frame or low tunnel, some hardy leaves keep going into late fall, and a protected bed gives better odds than an open one.