Frost dates for Ottawa, Canada
Half of years have their last spring frost by April 29, but 1 year in 10 still frosts after May 11.
A frost date is really a percentile from 30 years of records at a nearby weather station: 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 11
- 1 year in 5
- May 6
- 3 years in 10
- May 3
- 2 years in 5
- April 30
- Half of years (the median)
- April 29
First fall freeze
How often the first freeze comes on or before each date.
- 1 year in 10
- September 25
- 1 year in 5
- September 30
- 3 years in 10
- October 3
- 2 years in 5
- October 6
- Half of years (the median)
- October 10
- Growing season
- about 162 days
- Hardiness zone nearby
- 4b, from the US zone map at a ZIP code 76 km (47 miles) away
Where these numbers come from
NOAA NCEI 1991–2020 Climate Normals, the Ogdensburg 4 NE station (listed by NOAA as Ogdensburg 4 NE HCN, USC00306164), at 44.73, -75.44. These are that station’s own records, unshifted. The further your garden is from it, the less exactly they describe your ground. The planner finds the nearest station to your garden and lowers its confidence with distance, so no number is presented as if it were measured in your yard.
Ottawa is 79 km (49 miles) from this station, in New York, in the United States. The Milpa planner reads a weather station within 80 km (50 miles) before it reads a weather model, so a garden here gets these dates too, graded Promising.
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.
What can I plant here, and when? ›
Nearby cities
The nearest cities with a frost page here, and how their last-frost dates compare.
- Montreal, Canada, last frost by April 30
- Toronto, Canada, last frost by April 29
Other cities in Canada.
- Calgary, Canada, last frost by May 22
- Edmonton, Canada, last frost by May 10
- Vancouver, Canada, last frost by April 18