When looking for or giving gardening advice, one of the first questions that should be asked is what zone you are gardening in. Zones range from 0 to 12, extreme cold temperatures to tropical environments and help gardeners to identify which plants will survive within their zone.

Plants are typically described as hardy to a certain zone. For example mint is hardy to zone 4, which means it will survive cold temperatures down to -34C. All hardiness zones can also be subdivided into a and b (Ex. 4a and 4b), with b indicated a slightly warmer zone than a.

In 1960, the first hardiness map was developed by the United States Department of Agriculture. Based only on minimum winter temperatures, it provided the basis for future guides, many of which now take into consideration additional variables such as length of frost free periods, summer rainfall, maximum temperatures, and elevation. http://www.planthardiness.gc.ca/

Here in Canada, Agriculture Canada has a useful map you can use to determine which zone you are in and which plants are suitable to grow. This map was last updated in 2000 incorporating weather data, elevation and plant survival data.

We suggest using the map and your growing zone as the first variable in determining which plants to grow. Your results will vary based on microclimates (ex. growing in the city vs the countryside) as well as the reliability of snow cover. Snow acts as an insulator against the cold and having reliable snow cover can allow some plants on the edge of your zone to survive while having little snow another year can mean the same plants will not survive the cold winter.

Here’s a general guide for minimum temperature resistance for plants in various zones:

Zone 0a: < -53.9°C
Zone 0b: -53.9 °C to -51.1 °C
Zone 1a: -51.1 °C to -48.3 °C
Zone 1b: -48.3 °C to -45.6 °C
Zone 2a: -45.6 °C to -42.8 °C
Zone 2b: -42.8 °C to -40.0 °C
Zone 3a: -40.0 °C to -37.2 °C
Zone 3b: -37.2 °C to -34.4 °C
Zone 4a: -34.4 °C to -31.7 °C
Zone 4b: -31.7 °C to -28.9 °C
Zone 5a: -31.7 °C to -28.9 °C
Zone 5b: -28.9 °C to -26.1 °C
Zone 6a: -26.1 °C to -23.3 °C
Zone 6b: -23.3 °C to -20.6 °C
Zone 7a: -20.6 °C to -17.8 °C
Zone 7b: -17.8 °C to -15.0 °C
Zone 8a: -15.0 °C to -12.2 °C
Zone 8b: -12.2 °C to -9.4 °C
Zone 9a: -9.4 °C to -6.7 °C
Zone 9b: -6.7 °C to -3.9 °C
Zone 10a: -3.9 °C to +1.1 °C
Zone 10b: +1.7 °C  to +4.4 °C
Zone 11a: +4.4 °C to 7.2 °C
Zone 11b: +7.2 °C to 10 °C
Zone 12a: +10 °C to 12.8 °C
Zone 12b: > 12.8 °C

Like many activities, gardening is never constant and yearly fluctuations, global warming, and season extension techniques can all make a difference in how successful the plants be over the winter. See for yourself what grows best in your zone or talk to your neighbours, gardening friends, experts at your local plant nursery for other planting tips.

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