On the B.C. coast, hardy unusual roots such as parsnips, salsify and scorzonera go in from late March into spring. Frost-tender ones such as oca and yacon wait until frost risk has passed. Everything hangs on one number: Vancouver’s average last spring frost, March 18. In half of all years, frost comes later than that, so it marks the middle of a window rather than a safe date.
The short answer for British Columbia
Sow hardy roots from late March, a couple of weeks after the average last spring frost at Vancouver International Airport (March 18). Hold tender roots until mid-May at the earliest. Both timings come from one coastal weather station, and nothing on this page covers the Interior or the north.
Environment and Climate Change Canada’s 1981-2010 normals put the average last spring frost at Vancouver International Airport on March 18 and the average first fall frost on November 10. These are mean dates, not probability bands. In one spring out of two, the last frost lands after March 18. In roughly half of falls, the first frost arrives before November 10. A gardener who treats March 18 as “safe from here on” is betting on a coin flip. Counting straight from one average date to the other gives about 237 days, but that is not a promise of frost-free weather. It is two midpoints with a lot of scatter on either side.
Hardy roots tolerate that scatter, which is why they anchor the calendar. Tender ones don’t. The table gives typical timing for the Vancouver area, to be adjusted by what your own soil and weather are doing.
| Root type | Typical timing near Vancouver | What sets it |
|---|---|---|
| Parsnip, salsify, scorzonera | Direct sow from late March through April | Slow germination, long time to size up |
| Jerusalem artichoke | Plant tubers in March or April | Hardy tubers, tolerant of cool soil |
| Celeriac | Start indoors in late winter, transplant late April to May | Needs a long season and steady growth |
| Oca, yacon | Start indoors, plant out mid-May or later | Frost-tender, form roots late in the season |
Which varieties suit each type is a separate question, covered in The Best Unusual Roots to Grow in British Columbia. The wider picture of how these crops behave in the province sits in Growing Unusual Root Crops in British Columbia.
What will not work here
Sowing tender roots on the March 18 average. A single frost blackens oca and yacon tops, and since half of springs still have frost after that date, putting them out on it means losing them in many years. A frost-free stretch in mid-April proves nothing yet.
Wet cold soil is the second failure, and it belongs to the coast. At the Vancouver reference station, the mean daily minimum of the coldest month is 0.8 °C (33.5 °F). That is a mild winter by Canadian standards, and the typical coldest night barely touches freezing. Mild does not mean dry, though. Seed and tubers set into saturated March soil sit and rot, and slugs thrive in exactly these conditions. Parsnip seed, which already takes weeks to come up, is the most exposed. If a handful of soil squeezes into a cold, glossy clump, the sowing can wait a week without costing anything.
Summer brings the opposite problem. Coastal summers are typically dry, and a gardener who waters once a week will lose the slow germinators. Parsnip, salsify and scorzonera need the seed row kept evenly moist for the two to three weeks they take to emerge. A crust that forms and dries between waterings stops seedlings cold. Celeriac fails a different way: uneven watering leaves it with small, woody roots. A coastal bed that gets one deep soak a week and nothing between those soaks is a poor home for either.
Late sowing is a quieter mistake. The November 10 average first fall frost gives the coast a long autumn, which tempts people into sowing slow roots in June or July. Salsify and scorzonera sown that late will likely finish thin, because the days shorten and the soil cools well before they bulk up. Spring is the sowing season for these.
The largest failure is geographic. Applying Vancouver’s dates to the Interior, the north or any upland district will go wrong. Those districts run weeks behind the coast, and the slowest crops (oca, yacon, celeriac) are the first to fall short where the season is shorter. This page does not have frost dates for those places, so it cannot say how many weeks.
What changes across British Columbia
British Columbia is not one garden, and the numbers here prove it. The reference figure for Vancouver is Canadian plant hardiness zone 9a, from Natural Resources Canada’s 1991-2020 normals. That is the Canadian system, not a USDA zone, and it does not convert. Natural Resources Canada says plainly that there are no simple conversions between the two systems, since the Canadian one is built on seven climate variables and the USDA one on a single measure. A zone 9a in Canada should never be read as a USDA 9a.
That figure describes one reference city. This page holds no other zone for the province, so it cannot give the spread from the coast to the north. The honest answer is that there is no single zone for British Columbia, and a gardener 200 miles inland or a few thousand feet up is working with a different calendar. Check the Canada’s Plant Hardiness Site map from Natural Resources Canada and look up your own municipality there. Don’t borrow Vancouver’s number, and don’t take any page’s word for which zone your garden falls in.
There is also a mismatch in the periods. The frost dates come from 1981-2010 normals and the hardiness zone from 1991-2020. Both are useful, but they don’t describe the same thirty years, and on a warming coast that gap matters at the margins.
For readers in northern or upland districts, the direction of the shift is clear even without numbers. Push every spring sowing later by weeks, not days. Lean on the hardy crops, meaning parsnip, scorzonera and Jerusalem artichoke, and treat oca and yacon as experiments that need indoor starts and a sheltered spot. Celeriac may still work but needs the most careful transplant timing. If you can’t tell whether a crop will finish in your season, a small trial row costs far less than a full bed.
Where to check this for your own county
For a county-level calendar, start with the Government of British Columbia’s agriculture and seafood pages. B.C. is divided into regional districts rather than counties, but the idea is the same. What to look for is a planting calendar written for your area, and any list of varieties that have been trialled near you. Both beat anything printed on a seed packet written for the whole country.
A local recommendation will outrank this page for a plain reason. This is the provincial view. It draws on one coastal station, one set of normals and one reference zone, and it cannot see your valley’s cold air pooling, your slope or your elevation. A district calendar built from local frost records and local trials can. Where the two disagree, trust the local source.
If the provincial pages don’t post a calendar for your district, that gap tells you something too. Ask a local garden club, a seed-saving group or a nursery that sells root crops to people nearby. Their experience across several seasons is worth more than a single average date.
Checking this against your own garden
No date on this page outranks what your own bed is telling you. Three signs are worth watching, and none needs equipment.
The first is soil warmth by feel. Push your bare hand a few inches into the bed in the morning. If it feels cold and clammy, hold off on seed and tubers. A bed that warms early is likely a south-facing or well-drained spot. One that stays cold long after the neighbors’ soil has warmed is a low or shaded pocket, and your calendar should run later there.
The second is the first flush of male flowers on local shrubs. Hazel and alder catkins are male flowers, and when they loosen and shed pollen, the local late-winter warm-up has started. If they appear much earlier or later than in a neighbor’s yard, you are in a different microclimate from the one the regional averages describe.
The third is the first true leaves. Sow a pinch of radish seed as a scout in March and watch when the second set of leaves, the true leaves, appears after the rounded seed leaves. A fast arrival says your soil is warming well. A slow one says to wait, and to push the slow roots back accordingly.
Common questions
Can I sow on the average last frost date?
For hardy roots, yes, and many gardeners sow earlier. For tender ones, no. March 18 is a mean, so frost comes later in about half of springs, and oca and yacon won’t survive that.
Do oca and yacon need an indoor start in B.C.?
They are typically started indoors, then planted out once frost risk has passed. This page has Vancouver data only, so for other parts of the province, check local sources.
Can parsnips and similar roots stay in the ground over winter?
On the Vancouver coast, where the coldest month’s mean daily minimum is 0.8 °C (33.5 °F), hardy roots such as parsnip, salsify, scorzonera and Jerusalem artichoke typically hold in the ground. Wet soil and slugs are the bigger risks. This page does not have winter data for colder districts.
Is zone 9a a USDA zone?
No. It is a Canadian hardiness zone from Natural Resources Canada, and it does not convert to a USDA zone. Use Canadian zones with Canadian sources and plant lists.