Frost Risk Dates by Canadian City
Frost risk dates by Canadian city — not one average date, but the 10%, 25%, 50%, 75% and 90% probability dates for the last spring frost and first fall frost, straight from Environment and Climate Change Canada's climate normals. Plant to the risk you can live with, not to a single average that's wrong half the time.
At a glance: A frost-risk date is the frost date at a chosen probability. The 10% last-spring-frost date is the risk-averse one — plant frost-tender crops after it and only about 1 year in 10 brings a later killing frost. The 50% date is the median; the 90% date is the early, high-risk edge. For Toronto, the ~90%-safe frost-free window runs May 19 → Sep 22; the coin-flip (50%) window is May 04 → Oct 09. This table gives both frost ends at five probabilities for 19 cities. Free to cite with a link to this page.
How to read these dates
- Spring column = "last frost on or after this date." At the 10% date, only ~10% of years still get a frost afterward — the safe planting date. The 90% date is early: ~90% of years still frost after it.
- Fall column = "first frost on or before this date." At the 10% date, only ~10% of years have frozen already — the safe harvest/protect-by date. The 90% date is late: ~90% of years are already done.
- So the risk-averse pair is 10% + 10%: plant after the spring 10% date, harvest or cover before the fall 10% date, and you're frost-free on both ends in about 9 years out of 10. Use the 50% dates to gamble a longer season.
📥 Download the dataset
All 19 cities — spring & fall frost dates at 10/25/50/75/90% — as a free CSV.
Download CSV →📝 How to cite this data
Frost-risk (probability) dates by Canadian city, compiled by GrowersGuide.ca from Environment and Climate Change Canada Canadian Climate Normals 1991–2020.
Last Spring Frost — Plant Tender Crops After These Dates
Read across: the date the last spring frost (0 °C) falls on or after, at each probability. The 10% column is the risk-averse planting date; 90% is the early gamble. Cities ordered by their median (50%) date, mildest first.
| City | 10% safe |
25% | 50% median |
75% | 90% early gamble |
|---|---|---|---|---|---|
| Vancouver BC | Apr 21 | Apr 06 | Mar 26 | Mar 15 | Mar 04 |
| Victoria BC | Apr 30 | Apr 25 | Apr 14 | Mar 31 | Mar 22 |
| Windsor ON | May 09 | May 01 | Apr 22 | Apr 15 | Apr 10 |
| Montreal QC | May 15 | May 08 | Apr 29 | Apr 24 | Apr 20 |
| Toronto ON | May 19 | May 13 | May 04 | Apr 28 | Apr 17 |
| Ottawa ON | May 20 | May 13 | May 07 | Apr 26 | Apr 19 |
| London ON | May 21 | May 13 | May 07 | Apr 28 | Apr 20 |
| Halifax NS | May 26 | May 17 | May 08 | Apr 30 | Apr 26 |
| Quebec City QC | May 26 | May 18 | May 11 | May 05 | Apr 30 |
| Fredericton NB | May 31 | May 26 | May 16 | May 09 | May 02 |
| Kelowna BC | Jun 02 | May 25 | May 16 | May 05 | Apr 30 |
| Sudbury ON | May 31 | May 25 | May 17 | May 08 | May 04 |
| Charlottetown PE | May 30 | May 24 | May 18 | May 07 | Apr 30 |
| Saskatoon SK | Jun 07 | May 29 | May 22 | May 14 | May 08 |
| Edmonton AB | Jun 10 | May 31 | May 22 | May 16 | May 12 |
| Winnipeg MB | Jun 07 | Jun 01 | May 24 | May 17 | May 09 |
| Calgary AB | Jun 11 | Jun 05 | May 26 | May 19 | May 11 |
| Regina SK | Jun 15 | Jun 05 | May 28 | May 17 | May 10 |
| St. John's NL | Jun 16 | Jun 09 | Jun 01 | May 23 | May 18 |
First Fall Frost — Harvest or Protect Before These Dates
The date the first fall frost (0 °C) falls on or before, at each probability. The 10% column is the risk-averse harvest/protect-by date; 90% means the season is almost certainly over. Same city order as above.
| City | 10% safe |
25% | 50% median |
75% | 90% late gamble |
|---|---|---|---|---|---|
| Vancouver BC | Oct 15 | Oct 27 | Nov 04 | Nov 12 | Nov 24 |
| Victoria BC | Oct 17 | Oct 30 | Nov 05 | Nov 11 | Nov 23 |
| Windsor ON | Oct 07 | Oct 17 | Oct 25 | Nov 03 | Nov 11 |
| Montreal QC | Sep 28 | Oct 02 | Oct 09 | Oct 16 | Oct 21 |
| Toronto ON | Sep 22 | Sep 29 | Oct 09 | Oct 20 | Oct 30 |
| Ottawa ON | Sep 24 | Sep 28 | Oct 02 | Oct 09 | Oct 16 |
| London ON | Sep 26 | Oct 02 | Oct 11 | Oct 18 | Oct 26 |
| Halifax NS | Oct 03 | Oct 10 | Oct 17 | Oct 23 | Nov 01 |
| Quebec City QC | Sep 20 | Sep 24 | Oct 01 | Oct 09 | Oct 15 |
| Fredericton NB | Sep 14 | Sep 16 | Sep 24 | Oct 02 | Oct 07 |
| Kelowna BC | Sep 10 | Sep 17 | Sep 23 | Oct 03 | Oct 10 |
| Sudbury ON | Sep 14 | Sep 20 | Sep 27 | Oct 06 | Oct 12 |
| Charlottetown PE | Oct 06 | Oct 12 | Oct 17 | Oct 23 | Oct 30 |
| Saskatoon SK | Sep 01 | Sep 08 | Sep 15 | Sep 21 | Sep 27 |
| Edmonton AB | Aug 21 | Sep 03 | Sep 11 | Sep 19 | Sep 27 |
| Winnipeg MB | Sep 12 | Sep 16 | Sep 22 | Sep 28 | Oct 03 |
| Calgary AB | Aug 27 | Sep 03 | Sep 10 | Sep 19 | Sep 27 |
| Regina SK | Aug 22 | Sep 03 | Sep 11 | Sep 18 | Sep 23 |
| St. John's NL | Sep 28 | Oct 07 | Oct 15 | Oct 21 | Oct 26 |
Turning Probabilities Into a Planting Plan
- Price the risk. Expensive, frost-tender transplants (tomatoes, peppers, basil, cucurbits) → plant after the 10% spring date. Cheap, quick-to-re-sow crops, or if you keep row cover handy → the 25–50% date buys one to three weeks of earlier season.
- The spread is the point. The gap between a city's 10% and 90% spring dates shows how variable its last frost is — a wide spread (common inland and on the Prairies) means an "average" date is close to useless. St. John's has the latest 10% spring date here (Jun 16).
- Watch the fall end on the Prairies. A short season is squeezed from both ends: Edmonton can see its first fall frost as early as Aug 21 (the 10% date) — choose short-maturity varieties accordingly.
- Season extension shifts your risk, not the climate. Row cover, cloches, Wall-O-Water and low tunnels effectively let you plant to an earlier (riskier) probability while keeping the same odds of survival. That's the practical lever the distribution reveals.
Want the single-date version, or your exact town? The frost calculator gives local last/first frost by postal code, and the last-frost hub and first-frost hub carry per-city deep dives. This page is the risk distribution behind those averages.
Methodology & Sources
- Source. Every date is Environment and Climate Change Canada's published frost-probability normal from the 1991–2020 Canadian Climate Normals: "probability of last temperature in spring ≤ 0 °C, on or after (date)" and "… first temperature in fall ≤ 0 °C, on or before (date)."
- Threshold. 0 °C (a light frost). Tender foliage can be nipped at or just above 0 °C, and a hard freeze is −2 °C or colder; ECCC publishes those thresholds too, but this page uses the standard 0 °C set.
- Distribution period. ECCC computes each probability curve over the station's long-term daily-minimum-temperature record and publishes it within the 1991–2020 normals — a longer, more stable base than 30 years alone.
- Same-station rule. Each city is read from one long-record station, matched by Climate ID (in the CSV). A city is included only if both the spring and fall probability rows parse for all five percentiles; otherwise it is flagged and skipped — never reconstructed or estimated.
- Live-computed. The example window, latest-spring and earliest-fall figures and city ordering on this page are computed from the downloadable CSV on every load — nothing is hand-typed.
For researchers, master gardeners, societies & educators
This table is free to quote and republish — in newsletters, society bulletins, extension handouts, coursework or your own site — with credit to GrowersGuide.ca and a link to this page, and a credit to Environment and Climate Change Canada as the primary source. Want a city added, or the −2 °C hard-frost thresholds pulled too? Tell us: zusashicanada@gmail.com.
Every city added follows the same rule — same Climate ID, both probability rows present, or it doesn't go in.
Use of This Data
The compiled dataset on this page is free to use with attribution to GrowersGuide.ca (a link to this page is sufficient) and to Environment and Climate Change Canada as the primary data source. Provided as-is, without warranty; probability dates describe long-run odds and any single year will differ — verify against your own microclimate and a local forecast before acting.