Sow hardy Asian greens such as bok choy, tatsoi and mizuna outdoors from around May 30, the average last spring frost at the St. John’s airport station. Sow them again from late July so they finish before the average first fall frost on October 17. Both dates are midpoints, not guarantees, and the sections below show how to build a working window around them.
The short answer for Newfoundland and Labrador
The two dates come from Environment and Climate Change Canada’s 1981-2010 climate normals for the ST JOHN’S A station. They are average dates: May 30 for the last spring frost and October 17 for the first fall frost. In roughly one year out of two, the last spring frost falls later than May 30. Treat it as the middle of a window, never as a safe date. Between the two averages sit about 140 days.
Spring: from the midpoint, not before it
Hardy, fast types can go into the ground around May 30, or earlier under row cover if you accept the risk. Baby-leaf mizuna, tatsoi and komatsuna take frost better than most vegetables, which is why they suit this climate. Tender seedlings raised indoors need the frost risk to pass before they go out unprotected. Because May 30 is only the midpoint, plan a second small sowing two or three weeks later as insurance rather than betting everything on one date.
Late summer: count backward from October 17
This is the better season for most Asian greens. Sowings from late July into August mature in cooling weather, which avoids the bolting that long June days trigger. Baby leaves are ready in about a month, while full heads of bok choy take noticeably longer, so give heads the earlier end of that range. Work backward from October 17, and remember some years frost comes earlier.
| Type | Spring sowing | Late-summer sowing |
|---|---|---|
| Baby-leaf mizuna, tatsoi, komatsuna | Around May 30, earlier under cover | Into August |
| Bok choy heads | Start indoors, transplant after the frost risk eases | Late July |
| Napa cabbage | Risky, tends to bolt | Late July, with protection later |
| Heat-lovers such as water spinach | Not suited | Not suited |
For variety choices within each type, see The Best Asian Greens for Newfoundland and Labrador. For the wider picture, start with Growing Asian Greens in Newfoundland and Labrador.
What will not work here
Slow and heat-hungry crops
About 140 days between average frosts sounds generous until you subtract the cold, slow weeks at each end. A crop that needs long, warm weather to size up has little room. Water spinach is a tropical plant and sulks in any cool night, so it is a poor bet outdoors. Large napa cabbage heads, which want a long stretch of steady, cool growth, are a gamble in spring and tight in late summer.
The page does not have local summer temperature figures, so it cannot say how many warm days a typical season delivers. What the frost dates do show is the width of the season, and that width favors fast crops over slow ones.
Treating May 30 as a safe date
The biggest mistake is reading an average as a promise. If the last frost falls on May 30 in a typical year, then in about half of years it falls later. Tender transplants set out on that date, without cover, are the ones that get caught. The normals also cover 1981-2010, and your own recent springs may differ.
Overwintering in the open
The mean daily minimum of the coldest month at St. John’s is -8.7 °C (16.4 °F). That is an average, so individual nights run colder. Most Asian greens are not dependable through a winter like that without a cold frame or tunnel. Even the hardiest, such as tatsoi, are better treated as a fall harvest than as a plant that waits out the cold.
Dense planting in a damp season
A humid, cool season rewards airflow. Seedlings sown thickly and left unthinned stay wet and invite rot and slugs, which are a familiar garden problem in damp climates. This page has no rainfall figures, so treat this as a general caution rather than a measured one. Thin to the spacing on the seed packet, even when it feels wasteful.
What changes across Newfoundland and Labrador
Natural Resources Canada’s plant hardiness site lists the reference city for this page at zone 6a in the Canadian system, based on 1991-2020 normals. That is the Canadian zone of one city, not of the province. It is not a USDA zone and does not convert to one, because the Canadian system draws on seven climate variables and the USDA’s on one.
The province covers the island of Newfoundland and mainland Labrador, so there is no single answer. The page does not carry zone figures for other districts. The frost dates above come from one airport station, and northern or upland districts run weeks behind it. A garden on the Northern Peninsula or in Labrador will be working with a shorter window than the one described here.
If you garden in the north or at elevation, shift in three ways. Move the spring sowing later, because the soil thaws and warms later. Move the late-summer sowing earlier, because the first fall frost arrives sooner. Lean even harder on the fastest crops, such as baby-leaf mizuna and tatsoi, and use row cover or a low tunnel to stretch both ends.
To find your own zone, use the map on the Canada’s Plant Hardiness Site and look up your municipality. Do not assume your zone matches St. John’s.
Where to check this for your own county
The provincial agriculture department is the first stop: the Newfoundland and Labrador Department of Fisheries, Forestry and Agriculture. Look for a planting calendar for your own region, and for any list of vegetable varieties trialled near you. A variety that did well in a trial in your area is worth more than a general recommendation from a page like this one.
Newfoundland and Labrador does not organize gardening advice by county the way many US states do, so read “county” here as your local district. A local recommendation beats a provincial one every time, because it reflects your nearest weather records and the soils people actually garden on. This page is the provincial view, built from one station’s frost dates, and it should be corrected by anything more local you can find.
When you find a local calendar, compare its dates to the ones here. If the local dates run later, trust the local ones. If a local source gives no Asian-greens guidance at all, ask what it says about cool-season crops such as lettuce, spinach, radish and kale, which are the closest comparisons.
Checking this against your own garden
Your own observations outrank every date on this page. Three are worth watching, and none needs equipment.
- Soil warmth by feel. Push a hand into the bed in the morning. Soil that still feels raw and cold will give slow, patchy germination. A bed that warms sooner than a neighbor’s has a better microclimate, often from shelter and sun.
- The first male flowers. Alder and willow catkins loosening and shedding pollen mark the season turning in many gardens. Note the date each year. If they open noticeably later in your yard than in town, your spring is later too, and your sowings should follow.
- The first true leaves. Sow a small test row and watch for the first true leaves, the ones after the seed leaves. If they appear quickly, the bed is warm enough. If they stall or yellow, wait or add cover.
Keep a simple note of the date each of these happens. After two or three seasons you will have a calendar for your own yard that beats this one.
Common questions
Can I sow Asian greens before May 30?
Yes, with protection and the right type. Hardy, fast crops such as mizuna and tatsoi tolerate cool weather, and row cover helps. Since May 30 is an average, a later frost is possible, so sow small amounts early and hold the rest back.
When is the last good time to sow in fall?
Work backward from October 17, the average first fall frost at the St. John’s airport station, and allow for earlier frosts in some years. Baby-leaf types need the least time. Heads of bok choy need more, so they go in earlier.
Does the May 30 date apply across the whole province?
No. It comes from one station, and northern and upland districts run weeks behind it. This page does not have frost dates for other places, so check local sources.
Is zone 6a a USDA zone?
No. It is the Canadian zone for the reference city, built on seven climate variables, and it does not convert to a USDA zone. Check your own municipality on the national hardiness map.