Sow the hardy roots (parsnip, salsify, scorzonera) as soon as Quebec soil can be worked in spring, and hold frost-tender ones until after May 6, the average last spring frost at the Montréal/St-Hubert station. That date is a midpoint, not a safe date. Frost fell later than May 6 in about half the years behind it.
The short answer for Quebec
Direct-sow hardy roots such as parsnip, salsify and scorzonera in early spring, on or before the May 6 average last frost, and plant frost-tender roots such as oca and yacon only once that date has passed, with a margin of a week or two. The two frost dates in this page come from Environment and Climate Change Canada’s 1981-2010 normals for the Montreal/St-Hubert A station: last spring frost on average May 6, first fall frost on average October 5.
What those dates measure
Both are mean dates. In one year out of two, the last spring frost lands after May 6. A gardener who plants tomatoes-style on that exact day is betting on a coin flip. The dates describe the odds of frost, and they say nothing about when the soil is warm enough for a seed. Between the two means there are about 150 days, and that is arithmetic on two averages, not a guaranteed growing season.
A working calendar by type
| Root type | Examples | Window against the frost dates |
|---|---|---|
| Hardy, direct-sown | Parsnip, salsify, scorzonera | As soon as the ground is workable, before May 6 if the soil allows |
| Hardy perennial roots and tubers | Jerusalem artichoke, horseradish | Early spring, light frost is not a problem |
| Frost-tender, long season | Oca, yacon | After May 6 plus a margin, ideally started indoors, harvested around the October 5 average |
The middle row is the forgiving one. Perennial roots live through a Quebec winter underground, so spring timing matters less. The bottom row is where the calendar earns its keep. For a fuller look at which roots suit which gardens, see The Best Unusual Roots to Grow in Quebec.
What will not work here
Planting tender roots on May 6 and walking away. With the last frost falling later than that date in half of all years, an unprotected oca or yacon planting is exposed to a frost it has no defense against. A cold snap in mid-May is enough to set it back by weeks, and the weeks are exactly what these crops cannot spare.
Short-season thinking also defeats the slowest crops. The window from May 6 to October 5 is real, but a tender, long-season root needs most of it. Start it indoors late, or set it out in early June, and the first fall frost arrives while the roots are still small. Oca in particular bulks up late, so a frost that kills the tops in early October can cut the harvest off at the point where it should be growing fastest. Quebec’s calendar rewards hardy roots and punishes anything that needs every available day.
Late sowing of slow seed fails the same way. Parsnip, salsify and scorzonera are slow to germinate, and a seed bed that dries out in late spring is hard to rescue. Sowing them in late June, hoping they will catch up, leaves too little season for a full-size root. Early is better, even into cool soil.
Winter is the other limit. The mean daily minimum of the coldest month is -14.1 °C (6.7 °F), and that is the average of the lowest temperature each day, not an extreme night. It is cold enough that ground freezes and stays frozen. Tender roots left in the soil simply will not come through, so oca and yacon must be dug before hard frost and stored. Even hardy roots left in the ground become a chore to harvest if the soil freezes solid, so a thick mulch of straw or leaves over the row is worth the effort. Gardeners in milder US states can leave many roots in place all winter; here that habit needs a plan.
One more failure is quieter. Using the Montréal/St-Hubert dates for a garden hundreds of kilometers away. Those dates belong to one station. Northern and upland districts run weeks behind it, so a calendar copied from the south can put seed in the ground a month too early.
What changes across Quebec
Quebec is not one garden, and there is no single hardiness answer for it. The figure this page carries is Canadian hardiness zone 5b, from Natural Resources Canada’s 1991-2020 normals, and it describes the reference city, Montreal, not the province. Gardens to the north and at altitude sit in colder zones, and this page does not have the full spread of zones across the province, so it will not guess one.
Please keep one point straight: the Canadian zone is not a USDA zone. Natural Resources Canada builds its system from seven climate variables, where the USDA system uses one, and publishes the warning itself that there are no simple conversions between the two. Its own example: Canadian zone 4a overlaps nine different USDA zones, from 3a to 7a. A seed packet or nursery tag that gives a USDA number tells you little about a Quebec garden. To find your own zone, use the Canada’s Plant Hardiness Site map and look up your municipality.
The two sets of numbers also cover different years. The frost dates here come from 1981-2010 normals, while the hardiness zone comes from 1991-2020. Treat them as two rough guides rather than one matched set.
If you garden north of Montreal or at elevation, shift in three ways. Push the tender-root planting date later than May 6 by a margin you check against your own spring. Lean toward the hardy types and drop the crops that need the whole season. And start sowing the hardy ones the moment the soil is workable, because the spring window is short and the autumn one shorter. The general picture for the province is in Growing Unusual Root Crops in Quebec.
Where to check this for your own county
Quebec has no state extension service, so the nearest official starting point is MAPAQ, the province’s agriculture ministry. The page you are reading does not have a Quebec root-crop calendar from MAPAQ, so check what the ministry and your regional agricultural advisors publish rather than assuming one exists.
Look for two things. The first is a local planting calendar for your region, with sowing and transplanting dates keyed to your own frost pattern. The second is a list of varieties trialled where you garden, because a root that performs in the Montreal plain can sulk in the Laurentians or the Gaspé. A trial result from a nearby farm or research site beats any general rule.
A local recommendation beats a provincial one, and this page is the provincial one. It rests on a single station’s averages, a single reference-city hardiness zone, and a normals period that is already some years behind us. Use it to get oriented and to understand why the dates fall where they do. Then let the local calendar overrule it wherever the two disagree.
Checking this against your own garden
Your own observation outranks every date above. Three things are worth watching, and none needs an instrument.
- Soil warmth by feel. Grab a handful from the bed you plan to use. If it feels clearly cold to a bare hand, tender roots and slow seed will sit and stall. Wind-exposed or shaded beds stay cold longer, and that tells you which corners to save for hardy crops.
- The first true leaves. Sow a few radishes or lettuce ahead of the main crop. When their first true leaves (the ones after the rounded seed leaves) open, the soil is actually working. Compare how fast they move with a neighbor’s and you learn how your garden runs.
- The first male flowers on squash. Male blooms open before female ones, and the date they appear tells you how far into the warm season you really are. If they come late, your site runs cool and a slow root needs a head start.
Write the dates down for one season. By the second year you will have a calendar that beats the averages, because it is yours.
Common questions
Is May 6 safe for planting tender roots in Quebec?
No. It is the average last spring frost at the Montréal/St-Hubert A station, so frost came later in about half the years. Wait a week or two past it, or cover young plants.
When does fall frost end the season?
The average first fall frost is October 5 at that station. Plan to harvest tender roots by then, and note that an early frost can arrive sooner in colder districts.
Can I use these dates in northern Quebec?
Only as a starting point. Northern and upland districts run weeks behind the Montreal-area station, so shift your dates later and check a local source.
Is Canadian zone 5b the same as a USDA zone?
No. The Canadian system uses seven climate variables and does not convert to USDA zones. Natural Resources Canada notes that Canadian zone 4a alone overlaps nine USDA zones.