Plant hardiness refers to a plant's ability to tolerate extremes.
The most common extreme referenced, is to a plant's cold hardiness, sometimes referred to as just hardiness. A cold hardy plant can tolerate cold weather better than a plant that's not cold hardy.
Your area's average annual lower temperature determines your hardiness zone. If your low is -10'C, you would be in Zone 8 and would want to buy plants that can survive Zone 8 winters. It's generally assumed that a plant that can withstand the cold of Zone 8, it would also be fine in warmer zones.
Source: Natural Resources Canada
Hardiness zones can range from region to region, city to city and even from garden to garden.
The best way to determine your zone is to look up the average annual low in your area and apply that to the table below. Or better yet, ask a local, seasoned gardener - they'll know!
Zones range from 1a to 13b. Below are the most common zones for British Columbia.
Here are some additional resources to help you determine your plant cold hardiness zone:
- Natural Resources Canada: Plant hardiness maps
- Natural Resources Canada: Plant hardiness zones by municipality
- PlantMaps: British Columbia plant hardiness zone map
One final note: Your hardiness zone is not the same as your last average frost date. Your last average frost date is the last day that you are likely to have frost in your area - this is usually in the spring. It has nothing to do with the coldest day of the year, which is what determines your hardiness zone.