On the B.C. coast, the average last spring frost at the Vancouver International Airport station falls on March 18, which is early by Canadian standards. But celeriac, kohlrabi, horseradish and Jerusalem artichokes don’t plant by that date. They plant by soil temperature, and soil lags the frost date by weeks. The province also runs on many clocks, so the airport’s calendar is only a starting point.
When the soil is warm enough in British Columbia
The frost date, and why it is only a proxy
Environment and Climate Change Canada’s 1981-2010 normals for the Vancouver Int’l A station (climate ID 1108447) put the last spring frost, on average, at March 18. Read that as the middle of a window rather than a deadline. A frost date is a probability, not a promise: in one year out of two, the last frost lands later than the average. That is the only warning about the date you’ll get on this page, so keep it in mind.
The bigger issue is what the date measures. Frost tells you about air at night. These roots care about the soil, and soil warms slowly, particularly on the coast, where March and April ground can sit cold and saturated for weeks after the last frost has passed. Seed sown into cold, waterlogged soil tends to sit and rot rather than germinate. A cheap soil thermometer pushed in at planting depth each morning tells you more than the calendar does. The seed packet, or the provincial agriculture service, will name the minimum soil temperature each crop wants.
Different types wait for different things. Celeriac is usually started indoors and set out once cold snaps are behind you, because a long chill early in life can push it to bolt instead of swelling. Kohlrabi, turnip and rutabaga can be direct sown into cool but workable soil. Horseradish goes in as root pieces and Jerusalem artichokes as tubers, both once the ground is no longer sodden.
Site the Jerusalem artichoke before you plant it
Jerusalem artichoke is effectively permanent once planted. Every fragment of tuber left in the ground regrows, and digging the bed over only scatters more fragments. It is the planting gardeners most often regret, so choose its spot first: a corner you can fence off with a root barrier or accept as its permanent home, away from beds you rotate. Never put it where you plan to grow anything else later.
One more caution on the date. That March 18 figure belongs to a station near sea level in the Lower Mainland. Northern and upland districts run weeks behind it, and the Interior has its own pattern. Note too that Canadian normals cover 1981-2010, while the US figures elsewhere on this site cover 1991-2020, so don’t set the two side by side as if they were the same yardstick. If you garden anywhere other than the south coast, find your nearest local station’s normals and shift this page’s timing to match.
How long the season lasts here
The same station gives a first fall frost, on average, of November 10. Counting from March 18 to November 10 gives 237 days between the two mean dates. That is a long window by national standards. It is also a midpoint figure on both ends: the frost-free stretch can open late or close early in any given year, and the same station’s normals cannot speak for a valley in the Interior or a district in the north.
What does a window of that length allow? Mainly a second sowing. Quick roots such as turnip and kohlrabi can go in early, be harvested, and be followed by another sowing in summer for a fall crop, so the first sowing is not the only chance. The succession sowing guide on this site lays out how to space those rounds. A second go also lowers the stakes of a failed first sowing, since a cold wet spring that rots the early seed costs you a few weeks, not a year.
The long window also changes whether transplanting celeriac is worth the trouble. A short season makes transplanting a gamble: the seedling needs a clean root, because any check to its growth at transplant time eats into a season that has no slack. With 237 days between mean frosts, a seedling that sulks for a week after transplanting still has room to recover. It is the one root in this group that really needs the length.
Compare that with colder places. Gardeners who read Growing Unusual Root Crops in Manitoba will find a much shorter window in which first sowings must succeed, and Growing Unusual Root Crops in New York sits in between. For the broader picture of the whole group, see Celeriac, Kohlrabi, Horseradish and Jerusalem Artichokes. And if your garden is in the Interior or the north, do the same subtraction with your own local station’s two dates. This page can’t do it for you, and a guessed figure would be worse than none.
Heat and water in British Columbia
Two figures usually anchor this section: the number of days above 90 °F and the summer rainfall. This page has no verified value for either, so it won’t offer one. What can be said honestly is that the coast and the Interior differ sharply on both. Cool, damp summers bring slow ripening, mildew and fungal disease to the root bed. Hot, dry ones bring watering demands and stress at the root. Which of those applies to you depends on your district, and your local weather station’s own record is the place to check.
The two facts that do govern this group are season length and winter cold. Season length we have: 237 days between mean frosts at the Vancouver station, enough for celeriac, the long-season root, to finish there. Whether it can finish in a shorter-season district is a question for your own dates. A wet, cool summer will slow it and invite leaf disease, so airflow between plants and watering that keeps the leaves dry matter more than extra fertilizer.
The winter low decides the other question: whether roots stay in the ground or come out. At the Vancouver reference station, the mean daily minimum of the coldest month is 0.8 °C (33.5 °F, if you want the US comparison). Natural Resources Canada places the reference city in zone 9a of the Canadian hardiness system, which is not a USDA zone and does not convert to one, because the Canadian system draws on seven climate variables and the American on one. In practice, a winter that barely dips below freezing means horseradish and Jerusalem artichokes can stay put, and hardy roots can wait in the ground under a thick mulch until you need them. Farther inland and north, where the ground freezes hard, lift what you want to keep before the soil freezes and store it.
Storage touches food safety, so a few rules. Before storing, inspect every root. A soft patch, a weeping spot or a moldy crown ends the question: that root does not go into storage, and it does not go into the pot. A root that looks sound is not thereby proven safe. Keep stored roots cool, and check them regularly. No duration is promised here, because it depends on the crop, the condition at lifting and the place you keep them.
Turnip, rutabaga and kohlrabi are brassicas. They share their diseases and pests with cabbage, kale and mustard, including clubroot, a soil disease that persists once it is established. A gardener who rotates them into a cabbage bed has rotated nothing. Check the rotation page in this silo before deciding where each crop goes next season.
Which these root crops suit British Columbia
Choose by type, since this page has no list of varieties trialled in B.C. and will not make one up. What a gardener here can reason from are the territory’s facts. A long coastal window favours the full-season types, celeriac among them. A cool, damp summer makes disease resistance the first thing to look for on any seed packet. And a shorter season in the Interior or north favours the earliest types and makes a second sowing less likely.
| Type | What it needs | What to weigh in B.C. |
|---|---|---|
| Celeriac | Long season, steady moisture | Fits the coastal window; check your own dates inland; cool damp summers invite leaf disease |
| Kohlrabi, turnip, rutabaga | Cool, workable soil | Brassicas, so rotation and clubroot matter; early types suit shorter seasons |
| Horseradish | Deep soil, a permanent bed | Hardy, can overwinter under mulch where the ground stays soft |
| Jerusalem artichoke | Almost nothing | Hardy and permanent; site it first, away from rotated beds |
Two preparation notes belong here. Grating fresh horseradish releases compounds that genuinely burn the eyes and airways. Open a window, run a fan, and keep your face away from the bowl. Jerusalem artichokes store inulin rather than starch, and that causes digestive discomfort in many people. Start with a small first portion to find out how you respond. Neither cooking nor a frost is a guaranteed fix.
On varieties: British Columbia’s agriculture and seafood service is the place to ask which ones have been tried in your district. Local trial results are the only variety recommendation that carries weight, and this page does not hold them. Naming a cultivar without that evidence would be a guess dressed as advice, and a coast garden and an Okanagan garden would get the same guess, which makes it useless to both.
Common questions
When can I plant these roots in B.C.?
At the Vancouver airport station, the average last spring frost is March 18, but that is a midpoint and soil warms later. Plant when the soil is workable and warm enough for the specific crop, using a thermometer. Inland and northern districts run weeks behind the coast.
Can I leave roots in the ground over winter?
On the south coast, where the coldest month’s mean daily minimum is 0.8 °C, hardy roots, horseradish and Jerusalem artichokes can usually stay under mulch. Where the ground freezes hard, lift and store them first, and discard any root with a soft patch, weeping spot or moldy crown.
Is celeriac realistic in B.C.?
On the coast, yes: the 237 days between mean frost dates give the long-season root room. In shorter-season districts, count your own local frost dates before committing.
Which varieties should I buy?
This page names none, because it has no local trial data. Ask the province’s agriculture service for the types trialled in your area, and favour disease resistance if your summers run cool and damp.