On the south coast, sow hardy Asian greens such as bok choy and tatsoi outdoors from mid-March under cover, then again from late summer into early fall. The second window is usually the easier one. Every date below comes from a single weather station at Vancouver’s airport, so it describes the mildest corner of the province, not British Columbia as a whole.
The short answer for British Columbia
Sow Asian greens in British Columbia from mid-March in the mildest coastal gardens, and again from late summer into fall. The anchor dates are an average last spring frost of March 18 and an average first fall frost of November 10. Both were measured at Vancouver International Airport (Environment and Climate Change Canada’s Canadian Climate Normals, 1981-2010).
Each date is the midpoint of a window, not a safe date. In one year out of two, the last spring frost falls after March 18. In one year out of two, the first fall frost arrives earlier than November 10. Gardeners who treat either date as a guarantee lose seedlings in the bad half of years.
Between the two dates lie roughly eight months. The coldest month has a mean daily minimum of 0.8 °C (33.5 °F). That is the average overnight low in the coldest month, not the record low, and a cold snap can go well below it. It still explains why hardy greens can be sown early and left in the ground late on the coast.
For spring, hardy and fast types can go in around the March 18 mark with fleece or a low tunnel ready for the frost that may still come. For fall, count backward from November 10. Take the days to maturity on the seed packet, subtract them from that date, then add a generous cushion, because growth slows as the days shorten. This page has no single “last sowing date” to offer, and a fixed one would be false precision.
| Window | Anchor | What suits it | Watch for |
|---|---|---|---|
| Early spring | Mean last frost, March 18 | Hardy, quick greens under cover | Frost in the later half of years |
| Late spring to midsummer | Lengthening days | Little, apart from bolt-resistant types | Bolting, dry soil |
| Late summer to early fall | Count back from mean first frost, November 10 | Most Asian greens | Slugs, wet leaves, slowing growth |
Which types suit which window is a separate question, covered in The Best Asian Greens for British Columbia. For the wider picture of growing them here, see Growing Asian Greens in British Columbia.
What will not work here
Planting on March 18 and calling it done will not work. That date is a coin flip, not a finish line. A tray of unprotected seedlings set out on the average date faces a frost in about half of years, and a late one is more likely to hurt than a mid-winter one because the plants are tender and new.
The long, bright run into summer
A late-spring sowing meant for summer harvest tends to fail. Many Asian greens, bok choy especially, read lengthening days and stress as a signal to flower. Sown in May or June, they race to a flower stalk before they form a decent head. Coastal summers also tend to be dry, and a weekly soak does not suit a shallow-rooted green that wants even moisture. Dry spells turn the leaves tough and bitter and push bolting further. The page has no summer rainfall or heat figures, so treat those as general patterns, not measured ones.
Heat-hungry types and wet-fall crowding
The facts here contain nothing about summer heat. Greens that want sustained warmth are a gamble on a cool coast, and this page will not promise them. Check regional trial results before you commit a bed.
Close spacing is the other failure, and fall is when it bites. The first frost does not arrive until November 10 on average, and the coldest month still averages a mild 0.8 °C overnight. Slugs and leaf diseases are never fully shut off by a hard freeze here, and wet autumn foliage packed tightly stays wet. Crowded rows give both an easy start. Thin seedlings early and leave air between plants.
Finally, using the airport’s figures inland or up north will not work. The station sits at the mild end of the province. A garden in a cold interior valley or at altitude runs weeks behind it, and applying these dates unchanged there is the surest way to miss the window.
What changes across British Columbia
British Columbia is not one garden. The reference city here sits in zone 9a of the Canadian plant hardiness system (Natural Resources Canada, 1991-2020 normals, Plant Hardiness Zone by Municipality). That is the zone of one city, not of the province, and the page does not carry a province-wide spread, so there is no single answer to give.
The Canadian system is not the USDA system. It is built on seven climate variables, and NRCan says plainly that no simple conversion exists between the two. Don’t read 9a as a USDA zone, and don’t compare it with the US figures elsewhere on this site. The normals also differ: the frost dates cover 1981-2010, while the zone covers 1991-2020.
For a reader in a northern district, in the interior, or at altitude, the direction of the shift is clear even if the size is not. Start spring sowings later, finish fall sowings earlier, and lean on covers at both ends. Count back from your own first fall frost rather than November 10. The same quick, hardy greens still make sense, but the margin for slow types shrinks.
Nobody should take a zone from this page as their own. Look up your municipality on the NRCan map linked above, and check which municipality it lists nearest to you. A garden a few hundred feet higher or in a cold-air pocket can behave like a different zone from the town next door.
Where to check this for your own county
A regional recommendation beats a provincial one, and this page is the provincial one. Start with the B.C. government’s agriculture and seafood pages, the official provincial source for agricultural guidance.
Look for two things. The first is a planting calendar written for your area, whether a county, a regional district, or the nearest farming region. It should list sowing windows for leafy vegetables, and ideally for Asian greens by name. The second is a list of varieties trialled where you garden. A bok choy that performed in a coastal trial may bolt in a cooler, higher-elevation garden, and local results show that before you spend a season finding out.
If no Asian greens calendar turns up, a general cool-season vegetable calendar for your region is the next best thing. Match its dates for crops like lettuce and spinach, which share the same cool-weather habits. The page has not confirmed that any such calendar exists at that address, so treat it as the place to start looking, not a guaranteed answer.
Whatever you find, compare its frost dates with the ones here. If the local source gives dates weeks apart from March 18 and November 10, trust the local ones. They come from a station closer to your soil.
Checking this against your own garden
Your own observations outrank every date on this page. Three are easy and need no equipment.
- Soil by feel. Push a bare hand a few inches into the bed. Soil that feels cold and clings in a heavy lump is not ready for seed, and what you find shows how slowly your plot warms compared with the airport’s average.
- First true leaves. Sow a small test row early and note when the first true leaves, the ones after the seed leaves, appear. Slow arrival points to a cool spot, and a quick one means your garden is ahead of the regional pace.
- Your first frost in a low corner. Look for white on the grass or a frosted windshield, and note which part of the yard whitens first. The low corner that frosts early is your cold pocket, and it sets your fall deadline sooner than the average date does.
Keep a few dated notes over a season or two. They turn a regional average into a calendar that fits your own ground.
Common questions
Can I sow Asian greens outdoors in March in British Columbia?
On the south coast, yes for hardy, quick types, with cover. The average last frost at Vancouver International Airport is March 18, but in about half of years the last frost falls later. Inland and northern gardens should wait longer.
What is the last date to sow for a fall crop?
This page does not give one. The average first fall frost is November 10 at the airport station. Take the days to maturity from your seed packet, count back from your own first frost, and add a cushion for slowing growth.
Is 9a my hardiness zone?
Not necessarily. Zone 9a in the Canadian system is the zone of the reference city, not of the province, and it does not convert to a USDA zone. Check your municipality on the Natural Resources Canada map.
Why does my bok choy bolt in summer?
Lengthening days, dry soil, and stress all push many Asian greens to flower early. Sowing in late summer for a fall harvest avoids most of that, and steady watering helps in any season.