Hermantown event to teach gardeners about warming climate

Bob Olen had been working to develop a fall-fruiting raspberry that would produce well in northern Minnesota for years without much success. Until two years ago.

“We got really great yields the past two falls," the St. Louis County extension horticulturist said.

The better autumn-crop raspberries are probably the result of more summer and early fall “heat units" — higher temperatures during the growing season that allow better sugar production in the plant.

“It’s not just how cold it gets in the winter that matters for plants, it’s also how warm it gets during the growing season,’’ Olen said. “The growing season may be slightly longer, but we’re also getting more heat between frosts.”

That longer growing season, the northward movement of official planting zones, and a generally warmer environment in which to plant is the focus of this year’s Spring Gardening Extravaganza. The annual event brings together gardening experts and gardening enthusiasts and touches on subjects as diverse as garden photography, color schemes in gardening to match your home and how new hydrangea varieties will perform in northern Minnesota.

“Gardening in a Warming Northern Climate," set for Saturday at Hermantown High School, includes a program by National Weather Service meteorologist Carol Christenson on temperature trends for the region.

If you hadn’t noticed, that trend has been warmer. That’s not to say there won’t be very cold days, or that we won’t still see snow in April. But, on average, the extremes are warming, as are the seasons.

Olen said new shrubs, annuals and perennials are now options, as are warmer season vegetables and even new “deer-proof” ornamental grasses — all varieties that earlier generations of Northland gardeners probably would have avoided, or failed at if they tried.

Master Gardener Rick Boen of Duluth will show how to plant seeds now — and start them growing in hoop houses or indoors — for vegetables and flowers that still need more time in the ground than Northland summers offer. Tomatoes, peppers and eggplant, for example, need 100 days or more from the time the seed is planted.

“They may say ‘70-day variety,’ but that’s after it takes five or six weeks to get to the size you can transplant,’’ Boen said. “So you’re up over 100 days at that point. It’s not so much the temperatures late in summer or early fall. Even if it stays warmer, tomatoes just don’t do as well when the daylight starts to get shorter.”

Boen said warmer summers might help produce better crops of those vegetables and might even allow Northlanders to plant more southern crops.

“Green beans will do better. We could even see watermelon up here, which has been really hard to grow in this area,’’ Boen said.

The U.S. Department of Agriculture in January revised the official hardiness guide for the nation’s 80 million gardeners that shows zones moving north as winter temperatures aren’t getting as cold as often, and growing seasons are getting longer.

Much of the Iron Range, for example, moved from Zone 3A to warmer 3B under the new guidelines, meaning new and different plants and vegetables might grow because temperatures aren’t getting as cold.

Much of the Northland sits on the edge of Zones 3B and 4A, but areas near the warming influence of Lake Superior are squarely in warmer zone 4B. And Olen said some spots might be even warmer.

“We’re still not officially in Zone 5 yet, but for a lot of areas near the lake and in south-facing, sunny areas, I think people around here can try some Zone 5 varieties. I’m seeing it happen, but one cold winter could still get you," Olen said. “When you move just one-half a zone, you open up literally thousands of new plants.”

For more information or to pre-register, call (218) 737-2870.

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