Around Montreal, the average last spring frost lands on May 6, and the root crops in this group go in a little after that, once the soil has caught up with the air. The season is long enough for celeriac, kohlrabi, turnips, rutabagas, horseradish and Jerusalem artichokes, with celeriac the tightest fit. Those dates belong to one station southeast of the city, though, and much of the rest of Quebec runs behind it.
When the soil is warm enough in Quebec
Environment and Climate Change Canada puts the average last spring frost at May 6 at the Montreal/St-Hubert A station, using its 1981-2010 normals. That is a mean, not a guarantee. In one year out of two the last frost falls later, so read May 6 as the middle of a window. (The US figures on this site cover 1991-2020, so the two sets of dates don’t describe quite the same decades.)
Frost is also only a proxy. Celeriac, kohlrabi, turnips and the rest wait for warm soil, and soil warms after the frost risk ends, not with it. A cold, rainy second week of May can leave a bed sodden and chilled with no frost at all, and seed sown into it sits and rots while transplants stall. A cheap soil thermometer, read in the morning at planting depth, tells you more than the calendar does. If the bed is cold and waterlogged, wait.
The crops don’t all wait equally long. Kohlrabi, turnips and rutabagas, as quick or hardy brassica roots, tolerate cool soil better than celeriac, which is normally started indoors and set out as a transplant. Cold snaps after transplanting can push young celeriac toward flowering instead of a swollen root, so hardening off and a patient planting date matter more for it than for any other crop here. For how each one grows in general, see Celeriac, Kohlrabi, Horseradish and Jerusalem Artichokes.
Geography stretches the window further. Northern and upland districts of Quebec run weeks behind St-Hubert, so a gardener in the Laurentians or the Saguenay should treat May 6 as a floor and lean on MAPAQ, the provincial agriculture ministry, and on neighbors with a few seasons of records.
Site Jerusalem artichokes before you plant anything
This is the planting gardeners most often regret. Jerusalem artichoke is effectively permanent once it is in the ground, because every fragment of tuber left behind regrows the following spring. Digging the bed over only scatters the pieces. Give it a corner you can fence off or mow around, such as a field edge or a bed with a hard border, and never the middle of a vegetable plot. The stalks also grow tall enough to shade whatever sits on their north side.
Once the site is settled, the growing is simple. Tubers go in as soon as the soil can be worked in spring, and they ask for little else.
How long the season lasts here
The same station gives an average first fall frost of October 5. Count from May 6 to October 5 and the window is 152 days. Both dates are means, so in a given year the window may be shorter or longer, and it will be shorter wherever spring comes late.
What does 152 days allow? Not a lot of slack, but enough for options. For the quick roots (kohlrabi, small turnips), the window is long enough to sow once in spring and again in midsummer for a fall crop. Hardy brassica roots also keep growing through light fall frosts, so the October 5 date marks the end of tender crops, not of the harvest. The succession sowing guide on this site lays out how to space those sowings.
Celeriac is a different story. It is the slow member of the group, and with transplants set out after the last frost, a late May planting leaves little margin before fall. A season this length makes the first sowing the main event for celeriac, and it makes the transplant worth the trouble: starting seed indoors buys weeks that direct sowing cannot. The catch is the root check. Transplants that are pot-bound or handled roughly stall for a while after planting, and celeriac cannot afford to stall. Loosen the root ball gently and plant at the same depth it grew at.
Gardeners elsewhere work with very different arithmetic. Compare it with Growing Unusual Root Crops in Oregon or Growing Unusual Root Crops in Iowa, where frost dates and summer heat shift what the same crops need.
Heat and water in Quebec
The data behind this page doesn’t include a count of days above 90 °F (32 °C) at the reference station, or a summer rainfall total, and guessing at either would be worse than leaving them out. What can be said is that a northern climate does not call for a hot-climate playbook. Where summers run cool and damp, the trouble is slow ripening, mildew on foliage and rot in the root zone, not scorched leaves. Wet years push gardeners toward airflow between plants, raised or well-drained beds, and watering in the morning so foliage dries.
Two facts govern the group here. The first is season length. At 152 days, celeriac can finish in a typical year, but only if the transplants get away cleanly and spring doesn’t drag. A cold, wet June costs it more than any other crop in this guide. It also wants steady moisture, so a dry spell followed by a downpour can leave rough or split roots.
The second is the winter low. The mean daily minimum of the coldest month at the Montreal reference station is -14.1 °C (6.7 °F). That is an average of nightly lows, not the record, so individual nights go well below it. Natural Resources Canada puts the reference city in plant hardiness zone 5b on its Canadian scale, which is built on seven climate variables and does not convert to a USDA zone.
That low sorts the crops. Horseradish and Jerusalem artichokes are hardy perennials and can stay in the ground under mulch. Turnips and rutabagas can hold in the garden into late fall, but frozen ground and snow make later digging a gamble, so lift what you want for winter before the soil freezes. Celeriac and kohlrabi should come out before the ground freezes.
Stored roots need inspection, not trust. Check them regularly and discard any with a soft patch, a weeping spot or a moldy crown. A root that looks sound on the outside is not proof that it is safe, and a damaged one can spoil its neighbors.
Which these root crops suit Quebec
Choose by type, and let the local climate break the tie. A season of about 152 days favors the earliest-maturing types, especially for celeriac, where margin is thinnest. Humid summers make disease resistance the first criterion for everything else. Wherever summers turn hot, shade at the root and airflow between plants matter more.
| Crop | Fit for Quebec | Winter |
|---|---|---|
| Celeriac | Longest season; transplant, choose early types | Lift before the soil freezes |
| Kohlrabi | Quick; room for a second sowing | Lift before the soil freezes |
| Turnip, rutabaga | Hardy; tolerate fall frosts | Lift for winter storage |
| Horseradish | Perennial; fits any site | Stays in the ground under mulch |
| Jerusalem artichoke | Permanent; needs a contained site | Stays in the ground under mulch |
Turnip, rutabaga, kohlrabi and horseradish are all brassicas. They share their pests and diseases with cabbage, kale and mustard, so rotating them into a cabbage bed rotates nothing. Follow the rotation page on this site and keep them on a separate cycle.
No cultivar names appear here, and that is deliberate. This page cannot source what has been trialled in Quebec, and a variety that thrives near Montreal may sulk in the Saguenay. MAPAQ and local growers know which varieties have been tried where, and that is the only recommendation worth planting on.
Two kitchen notes. Jerusalem artichokes store inulin instead of starch, and many people get digestive discomfort from them, so start with a small first portion. And grating fresh horseradish releases compounds that burn the eyes and airways: ventilate the room and keep your face away from the bowl.
Common questions
When do I plant these in the Montreal area?
After the average last frost of May 6 at the St-Hubert station, and only once the soil has warmed. That date is a mean, so half of all years see a later frost. Check the soil, not just the calendar.
Is Quebec’s zone 5b the same as USDA zone 5b?
No. The Canadian system uses seven climate variables and the USDA system uses one, and Natural Resources Canada says there is no simple conversion. Name the system whenever you cite a zone.
Can celeriac finish in a Quebec season?
In a typical year, yes, from transplants set out after frost within a 152-day window. A cold, late spring leaves it the least margin of any crop here.
Can I leave everything in the ground over winter?
Only the perennials, horseradish and Jerusalem artichokes, under mulch. The mean daily minimum of the coldest month is -14.1 °C (6.7 °F) at the reference station, so lift celeriac and kohlrabi before the soil freezes. Cold nights run well below that average.