Frost dates for Calgary, Canada
Half of years have their last spring frost by May 22, but 1 year in 10 still frosts after May 31.
A frost date is really a percentile, here from 30 years (1991 to 2020) of a weather model’s daily lows near Calgary: in about half of years a frost still comes after the median date. Both numbers are below, so you can choose the risk yourself.
The odds
Last spring frost
How often a frost still comes on or after each date.
- 1 year in 10
- May 31
- 1 year in 5
- May 27
- 3 years in 10
- May 26
- 2 years in 5
- May 25
- Half of years (the median)
- May 22
First fall freeze
- Half of years (the median)
- September 20
- Growing season
- about 120 days
- Hardiness zone nearby
- 4a, estimated from the weather model
Where these numbers come from
Modeled, not measured. No weather station stands behind these dates. They come from ERA5, a reconstruction of the world’s weather from 1991 to 2020 made by ECMWF, Europe’s medium-range weather forecasting agency, for the EU’s Copernicus program, and read here through Open-Meteo. They are the model’s daily lows for the point at 51.25, -114.25, 22 km (14 miles) from the center of Calgary. A frost here means a low at or below 0 °C (32 °F).
A weather model sees the land in squares about 25 km (16 miles) across, so it can miss what sets one garden apart from the next: a frost hollow, a hillside, a lakeshore, a city’s own warmth. The Milpa planner reads these same numbers for a garden here and grades them A good hunch.
Cold air also pools in low ground on the clear, still nights when frost happens, so a hollow can freeze while a slope a few hundred feet away does not. No table can know that about your garden. Your own logged frosts eventually can.
Weather data by Open-Meteo.com, under CC BY 4.0. Contains modified Copernicus Climate Change Service information, 2026.
What can I plant here, and when? ›
Nearby cities
The nearest cities with a frost page here, and how their last-frost dates compare.
- Edmonton, Canada, last frost by May 10
- Vancouver, Canada, last frost by April 18
Other cities in Canada.
- Toronto, Canada, last frost by April 29
- Ottawa, Canada, last frost by April 29
- Montreal, Canada, last frost by April 30