Terry Skillin, president and owner of Skillin’s Greenhouses in Brunswick, Cumberland and Falmouth, has begun to notice that local gardeners are having greater success growing more southern varieties of produce such as tomatoes, peppers and melons.

It’s a sign that Maine and the nation are getting hotter, according to a new analysis by the U.S. Department of Agriculture.

The USDA’s new plant hardiness zone map, which was released last week, shows how growing zones have changed since the last growing guide was published 22 years ago.

The map is considered the standard by which gardeners and growers can determine which plants are most likely to thrive in a specific geographical location.

The new plant hardiness zone map — the old map was published in 1990 — is based on temperature data gathered over a 30-year period between 1976 and 2005. It was jointly developed by the USDA’s Agricultural Research Service and PRISM, a climate group based at Oregon State University.

In Maine, the biggest shifts occur in the midcoast and York County.

On the new map, the midcoast of Maine and the southern portion of York County have moved from zone 5b to zone 6a. The rest of the area along the Maine coast, including parts between the new 6a zones, remains at 5b.

The average annual extreme cold temperature in zone 5b is minus 10 to minus 15 degrees. The average annual extreme cold temperate in zone 6a is minus 5 to minus 10 degrees.

“We’re definitely starting to grow things that our counterparts have been selling for years in Connecticut and Massachusetts,” Skillin said. “But Mainers won’t be growing oranges or bananas anytime soon.”

For the first time, the map offers a Geographic Information System-based interactive format and is specifically designed to be Internet friendly. The online map also offers a find-your-zone-by-zip-code feature.

Lois Stack, who was cooking home grown winter squash for dinner Thursday night, grows all her own vegetables at her home in Hampden.

She is employed as an ornamental horticulture specialist for the University of Maine Orono’s Cooperative Extension Service. Stack has been a professor of sustainable agriculture at the University of Maine since 1987.

Stack spent part of her day on Wednesday studying the new map and how it will affect Mainers. She was impressed with its level of detail and specific growing boundaries.

“Now, we can use this map to say where a particular plant can be grown,” Stack said. “That helps a gardener to say, ‘OK this plant is only hardy in a certain zone. I shouldn’t consider that for my garden.'”

Stack said the challenge for gardeners will be deciding whether to grow a plant or even a tree that might be borderline in terms of the zone it can survive in.

Stack said Maine gardeners might try to grow more varieties of rhododendron, a flowering woody shrub.

Amatuer gardener Anne Hagstrom of Yarmouth, who was shopping for houseplants at Skillins in Falmouth on Saturday, said she wants to experiment with plants she wouldn’t have tried before in her community garden plot this summer.

“But at the same time, I am wishing this was not the result of climate change,” Hagstrom said.

Seth Kroeck, who has been farming at Crystal Spring Farm off Pleasant Hill Road in Brunswick for nine years, said the new map won’t really affect his work. But he does agree that the growing season has been getting longer and warmer.

“Our frost dates are pushing back in both directions,” said Kroeck.

Two years ago, Kroeck said, he started turning ground in early March and last year the first killer frost didn’t arrive until late October. He said it feels as if the summers are getting warmer, making for a long and productive growing season.

“As a professional grower, the map doesn’t have a great impact on me, but it should help some of the new gardeners decide what to grow,” he said.

Kroeck is already thinking about the upcoming growing season. Seed catalogs started arriving this month.

“It’s a good time to curl up next to the wood stove with a seed catalog,” he said.

Richard Brozozowski, a University of Maine cooperative extension educator from Falmouth, teaches master gardener classes and said the new map does open the door for gardeners to try new varieties.

“Gardeners in Maine have tried growing everything, from peanuts and figs to sweet potatoes and kiwi,” he said. “They pushed the envelope.”

Brozozowski said peaches, grapes and okra might be able to thrive in Maine.

He suggested gardeners keep an eye on their property and watch where the snow melts first. He said warm pockets of land are good places to start a garden.

Tom Settlemire, retired from a career of more than 35 years as a biology professor at Bowdoin College, gardens and raises sheep in Yarmouth.

Settlemire is excited about the new map because it shows that ryegrass might grow in Maine. Ryegrass is a high-energy, high-protein grass that cattle and sheep graze on. It is grown extensively in places such as Australia and New Zealand.

“The problem has been that our cold winters freeze it out,” he said.

But if ryegrass could be grown here, it could have a positive impact on the cattle and sheep industry.

Not everyone is excited by the USDA’s new zone configurations.

Jeffrey O’Donal, who owns O’Donal’s Nursery on the Gorham/Scarborough town line, said the new map did not contain any surprises. He doubts that gardeners in Maine will start to grow plant species that might not otherwise have thrived here.

“In my opinion, none,” O’Donal said. “The real proof will be in the pudding. If you plant a plant and it dies, it doesn’t matter what the map says.”