Pick fast, cool-season leaf greens: mizuna, tatsoi, komatsuna, baby bok choy and mustard types. They fit New Brunswick’s frost-free stretch of a little over four months, and they shrug off the chilly edges of spring and fall. Slow heading types and heat lovers are where gardeners get burned. For the full picture of the crop, start with Growing Asian Greens in New Brunswick.
The short answer for New Brunswick
Choose by type: quick leaf greens first, a timed late-summer sowing of napa cabbage and full-size bok choy second, and skip the tropical heat lovers. The reason is the calendar. At the Moncton station, Environment and Climate Change Canada’s 1981-2010 normals put the last spring frost on average on May 23 and the first fall frost on average on October 2.
Those are mean dates, not safe dates. In one year out of two the last spring frost lands after May 23, and in one year out of two the first fall frost arrives before October 2. Think of each date as the middle of a window, not the edge of one. They also come from a single station, and the normals cover 1981-2010, a different stretch than the 1991-2020 figures used for the US pages on this site.
| Type | Examples | Verdict here | Timing logic |
|---|---|---|---|
| Quick leaf greens | Mizuna, tatsoi, komatsuna, mustard greens, baby bok choy | Best bet | Sow as soon as the soil is workable, then again in late summer; harvest young |
| Heading types | Napa cabbage, full-size bok choy | Workable with timing | Sow in summer so heads fill in the cooling weather of fall, counting back from the October 2 mean with a margin |
| Flowering stems | Choy sum | Fair, in cool spells | Early spring or early fall, harvested before it runs to seed |
| Heat lovers | Water spinach, amaranth greens | Not worth bed space outdoors | Need sustained warm soil that a May 23 to October 2 season rarely supplies |
Leaf greens win because of speed. Baby leaves of mizuna or tatsoi can be cut in roughly a month, so a short season barely touches them, and a light frost only sweetens them. That gives you two sowing windows a year, one in spring and one in late summer, with the quiet middle of the season left to the crops that like it hot.
Heading types are a different bet. Napa wants to form its head while days shorten and nights cool, which in New Brunswick means a sowing in the summer, not the spring. Counting back from the October 2 mean leaves little slack, so a few extra weeks of margin is sensible. Exact sowing dates are laid out in When to Sow Asian Greens in New Brunswick.
What will not work here
Napa cabbage sown in early spring is the classic failure. Long days around the June solstice push it to bolt before a tight head forms, and you end up with a flower stalk where dinner should be. Sow it too late instead, say at the very end of summer, and you are betting on the half of years when the fall frost arrives after October 2.
Heat lovers lose on arithmetic. Water spinach dies at the first touch of frost and sulks in cold soil. With a last-frost mean of May 23, meaning a coin flip on whether frost comes later, you cannot even set transplants out in mid-May without risk. Then you have barely four months of season to bring in a plant bred for the tropics. A greenhouse or a hot, sheltered bed might manage it. An ordinary vegetable plot will mostly produce disappointment.
Winter is the next wall. The mean daily minimum of the coldest month at Moncton is -13.9 °C (6.9 °F for readers comparing with the US). That is an average night, so real cold snaps run well below it. Tatsoi and mizuna take several light frosts without complaint, but they are not plants that sit through a New Brunswick January in an open bed. Treat them as spring and fall crops. Under a cold frame or tunnel you can stretch the fall harvest, but wintering over outdoors is a different project.
Spring sowings have their own problem in the form of flea beetles. These tiny jumping insects riddle the leaves of Asian greens and other brassicas with small holes, and young seedlings suffer most. A floating row cover laid on at sowing and tucked in at the edges is the usual fix. The same cover buys a little extra warmth in a cold May, which helps in a place where the last frost is a toss-up well into late May.
Last, sowing by date alone. If you read May 23 as “safe to plant,” you are treating a midpoint as a deadline. The hardy greens do not need it, since they can go in weeks earlier, but anything tender planted on that date has roughly even odds of meeting a frost afterward.
What changes across New Brunswick
The frost dates above belong to Moncton. A province is not one climate, and northern or upland districts run weeks behind that station. So there is no single answer for New Brunswick, only a spread that depends on where the garden sits.
The zone figure for the reference city is 5a on Canada’s hardiness system, from Natural Resources Canada’s 1991-2020 normals. That is a Canadian zone, not a USDA zone, and the two do not convert. Canada’s system is built on seven climate variables, the USDA’s on one, and Natural Resources Canada itself notes that a single Canadian zone such as 4a overlaps nine USDA zones, from 3a to 7a. This page has the figure for Moncton only, so it cannot tell you your own zone. Look up your municipality on Natural Resources Canada’s Plant Hardiness Site instead.
What should a reader in the north or on higher ground shift? Three things, mostly. First, push spring sowing later and lean on the hardy leaf greens, which tolerate cold soil better than anything else here. Second, pull the late-summer sowing earlier, because the fall frost will come before the Moncton mean, not after it. Third, accept that napa and full-size bok choy get riskier the shorter the season, and plan to protect them with row cover or a low tunnel if you try them.
Differences also show up inside a single property. A south-facing bed against a wall warms sooner than a low spot where cold air pools. Coasts and interiors often behave differently, too, though this page has no figures to quantify that.
Where to check this for your own county
A county recommendation beats a state one, and this page is the province-wide one. It rests on a single station and a handful of national datasets, which is fine for choosing a type but too coarse for picking a sowing date. For that, go to the people who garden your region.
Start with Agriculture and Agri-Food Canada, the federal department, and follow its links to New Brunswick’s provincial agriculture department. This page does not have a New Brunswick county calendar to give you, and it will not borrow a neighbor’s. What you want to find are two things. One is a local planting calendar with frost dates for the station nearest you, not Moncton by default. The other is a list of varieties trialled in your area, because a variety that performed in a field trial nearby tells you more than any catalog description.
If the department’s pages do not list them, ask. Regional agricultural offices, local garden clubs and farmers’ market growers who sell greens in October have usually worked out what the local season allows. A grower who has sold bok choy at your market for ten years knows the frost dates for your valley better than a normals table does.
When you do find a local calendar, compare its frost dates with the ones above. If the nearest station’s last spring frost is later than May 23 or its first fall frost earlier than October 2, shift your windows by that difference. The type-based logic on this page still holds. Only the dates move.
Checking this against your own garden
Your garden’s own signals outrank every date on this page. Three are worth watching, and none needs an instrument.
Soil warmth by feel. In spring, push a hand into the bed a few inches deep. Soil that crumbles and no longer feels icy is ready for hardy greens, and a bed that reaches that point days before the one across the yard has a warmer microclimate. Do the same in August: soil that stays cool to the touch tells you where lettuce-like crops will resist bolting.
The first male flowers. Alder and willow catkins loosening and shedding pollen mark the real arrival of spring in your spot. Note the date each year. If they open early on your lot, your spring window probably opens early too, and if they lag, hold off on the second sowing.
The first true leaves. Seedlings first show two rounded seed leaves, then the true, shaped leaves of the plant. Sow a small test row and watch for them. Fast true leaves mean the bed is warm and sheltered. Slow ones, or a seedling that stalls, tell you the site is colder than the calendar assumes, and that row cover or a different bed would pay off.
Write all three dates in a notebook for a couple of seasons. They will tell you more about your bed than a regional mean ever could.
Common questions
Can I grow bok choy in New Brunswick?
Yes, with attention to timing. Baby bok choy is quick enough for spring and late-summer sowings. Full-size heads do better sown in summer so they mature in cooling fall weather, ahead of the October 2 average first frost, which half of years beats.
Which Asian green is the most reliable here?
Among the types on this page, the quick leaf greens such as mizuna, tatsoi and komatsuna are the safest, because they mature fast and tolerate cold. Mustard greens are similar, though they bolt faster as days lengthen.
Is May 23 a safe date to plant tender seedlings?
No. It is the average last spring frost at Moncton, so in one year out of two a frost arrives later. Hardy leaf greens can go in well before it. Tender crops need a margin and a way to cover them.
Can Asian greens stay in the ground over winter?
Not in an open bed. The mean daily minimum of the coldest month at Moncton is -13.9 °C, and real cold snaps go lower. Use them as spring and fall crops, and consider a cold frame or tunnel if you want to extend the harvest.