March 14, 2024
Revised plant hardiness zone coming this year

Revised plant hardiness zone coming this year

Natural Resources Canada scientists are hard at work revising the plant hardiness zones map for the first time since 2010. The revision follows the release of ‘climate normals’ data — looking at climate information from 1991 to 2020.

“We develop new models based on the new time period and to see if there are any changes in the average conditions for each of the seven variables used in the plant hardiness formula,” said Dan McKenney, climate scientist with Natural Resources Canada. These factors are:
  • Mean minimum temperature of the coldest month
  • Frost-free period in days
  • Rainfall June through November
  • Mean maximum temperature of the warmest month
  • Rainfall in January
  • Mean maximum snow depth
  • Maximum wind gust in 30 years

“Any change usually varies across the country and some places seem to change more than others,” said McKenney. “In the past the west has changed the most, which is consistent with what is expected due to a changing climate.”

For landscape professionals, the new map may mean that new or different plants become more possible to experiment with. “The tricky thing is that this is based on ‘average’ conditions and each year there will always be some variability in performance and growth of plants from year to year.”

While there is no firm date for the new maps, McKenney says they will be released later in 2024.