A long-term warming trend has seen shrubs and bushes, previously considered impossible to grow in Calgary, sprouting in the city.

Many major cities have seen their planting zones altered to reflect the change in conditions.

Hydrangeas had been an uncommon sight in Calgary gardens but that didn’t deter longtime gardener Rick Bron, the owner of calgaryplantsonline.

“I've been doing experimenting with it for a long, long time,” explained Bron. “I used to grown endless summer hydrangeas at my house in Calgary 10 years ago and they came back every year when everybody said ‘No, those don't grow here’.”

Bron’s yield has made believers out of his critics and hydrangeas have become increasingly popular.

Several shrubs that, as a rule of thumb, don't grow here are thriving.

In 2016, Calgary’s plant hardiness designation was moved from Zone 3b to Zone 4a. The new category indicates a greater variety of plants will grow in the region during an extended growing season.

“If you're willing to experiment, it's an open book,” said Kari Baker of Bedworx Fine Gardening & Design. “You'll definitely get more colours and maybe things you haven’t seen before. That’s exciting!”

The zoning is based on the number of frost free days and the coldest temperatures reached during past winters.

Data recently released by Natural Resources Canada indicates that, over the past 30 years, Canada is experiencing a warming trend.

Plant hardiness zoning changes include:

  • St. John’s – Zone 6a (previously Zone 5b)
  • Ottawa – Zone 5b (previously Zone 4a)
  • Winnipeg - Zone 4a (previously Zone 3a)
  • Edmonton - Zone 4a (previously Zone 3b)
  • Calgary - Zone 4a (previously Zone 3b)
  • Kelowna – Zone 7a (previously Zone 6b)

CTV Calgary meteorologist Steve Rothfels says the zone changes are further proof of climate change.

“It is happening,” said Rothfels. "One of the aspects of it that a lot of gardeners and naturalists will notice is that there are things that can be grown here that you couldn’t grow 20 or 30 years ago.”

Gardeners eager to experiment with planting should brace for a period of trial-and-error.

“We're getting more into the heucheras, the coral bells, more hydrangeas,” said Bron. “There are some that are working, some that aren't.”

Despite its new designation, Calgary’s unusual weather patterns, including Chinooks and frost-thaw cycles, will continue to play havoc with delicate plants.

“Just make sure you’re really watering your plants in the fall, water in the spring and water throughout,” explained Baker.

For additional information on Plant Hardiness Zones, visit Natural Resources Canada.

With files from CTV’s Amanda Singroy