Growing zones · Lethbridge
Lethbridge growing zone: zone 4b
Lethbridge, Alberta is in plant hardiness zone 4b on the current Natural Resources Canada map (4th edition, based on 1991–2020 climate normals). The average last spring frost is around May 20 and the first fall frost around September 17, giving about 119 frost-free days at Lethbridge Airport, 8 km away.
Planting, hardiness and grow zone in Lethbridge
"Growing zone", "planting zone" and "hardiness zone" all refer to the same thing in Canada: the plant hardiness zone, which predicts which perennials, trees and shrubs survive the winter. It does not tell you when to plant vegetables; frost dates do that.
Zone 4 is the mildest band in Alberta, mostly in the south and in sheltered urban areas. Chinook thaws are the main winter risk.
- Wider choice of apples, plums, pears and grapes rated to zone 4
- Haskap, saskatoon, cherries and berries
- Many perennials rated zone 4, ideally in sheltered spots
- Shelterbelts against wind are still essential, especially in the chinook belt
- Longer warm season for squash, corn and beans in the irrigated south
Buy perennials rated for zone 4b or colder. Cold-air pockets, low ground and exposed sites in and around Lethbridge can run a full zone colder than the map.
Frost dates near Lethbridge
Average dates from Environment and Climate Change Canada's 1991–2020 climate normals at the stations nearest Lethbridge. Stations in towns usually show a longer season than open farmland nearby, which is why the numbers differ: nearby stations range from 103 to 119 frost-free days.
| Station | Distance | Last spring frost | First fall frost | Frost-free days |
|---|---|---|---|---|
| Lethbridge Airport | 8 km | May 20 | September 17 | 119 |
| Monarch | 27 km | May 28 | September 10 | 103 |
Growing degree-days above 5 °C average about 1,761 a year at Lethbridge Airport (8 km), and total precipitation about 380 mm at Lethbridge Airport (8 km).
When to plant in Lethbridge
- Cool-season crops (peas, spinach, lettuce, radish, potatoes) can go in a few weeks before the last frost, once the soil can be worked.
- Frost-tender crops (tomatoes, peppers, squash, beans, cucumbers) go out after the last frost, around May 20 on average, and many local gardeners wait an extra week.
- Trees, shrubs and perennials rated zone 4b or colder can be planted in spring or early fall.
Common questions
What growing zone is Lethbridge, Alberta?
Lethbridge is in Canadian plant hardiness zone 4b on Natural Resources Canada's current map (4th edition, 1991–2020 climate normals). Average frost dates there are about May 20 (last spring frost) and September 17 (first fall frost).
When is the last frost in Lethbridge?
On average around May 20, based on Environment Canada's 1991–2020 normals at Lethbridge Airport. Frost can come later in low spots and in cold years, so many gardeners wait about a week past the average before planting tender crops.
Is Lethbridge zone 4b on the USDA map?
Not necessarily. The USDA map uses only the average coldest winter temperature, while the Canadian map also weighs frost-free days, rain, snow cover and wind, so the two numbers often differ by about half a zone. Check which system a plant label uses.
Nearby places: Taber (4a) · Cardston (4b) · Claresholm (4a) · Pincher Creek (4b) · Brooks (3b) · High River (4a)
Land around Lethbridge: Lethbridge County farm guide · Lethbridge County hardiness zone · all Alberta growing zones · Canadian vs USDA zones explained
Sources: Natural Resources Canada, Plant Hardiness Zones of Canada (4th edition, 1991–2020); Environment and Climate Change Canada, Canadian Climate Normals 1991–2020. Page reviewed 2026-10-09.