This winter is a tough test of true Zone 5 plants

By Barb Delisio

OSU Master Gardener Volunteer

Hardiness zones tell us what plants we can grow successfully in our area. We are considered a Zone 5 for plants that will survive our winter temperatures. Zone 5 is our average highs and lows as well as distribution of rainfall that certain plants need to survive. This winter may be a test of true Zone 5 plants, and many of us who have tried Zone 6 plants with some mixed success will find the plants did not survive this winter of the “polar vortex.”

The United States Department of Agriculture provides these zone maps, which divides North America into 11 zones from the coldest Zone 1 to the warmest Zone 11. Each zone is 10 degrees warmer or colder in an average winter than the adjacent zone. The eastern half of North America is somewhat flat so the lines are drawn approximately parallel to the Gulf Coast every 120 miles as you move north. The lines lose their parallel status and tilt northeast the further north they go.

This fall, we took a trip to Nova Scotia and Prince Edward Island. While walking through a blueberry farm in Nova Scotia, I noticed they were growing the same things we grow here in our area: blueberries, tomatoes, potatoes, onions, etc. The farm grew blueberries, 350 bushes, for use commercially in Betty Crocker Wild Blueberry Mix. I questioned the head gardener about them. We were definitely much farther north than I would have thought they would have survived. He told me they are a Zone 5B, because of their nearness to the ocean and the gulf stream. When I got home, I immediately checked a hardiness zone map and was surprised how far Zone 5 went along the ocean. Due east of Youngstown, and all the way toward the Atlantic Ocean is Zone 7. Same latitude, but that ocean current makes the growing conditions warmer.

Hardiness really isn’t a problem with annual flowers because we know they last one season, then die at the first frost. The problem comes into play when you purchase bulbs, perennials, shrubs or trees. All plants expected to last longer than one growing season in our area must be labeled Zone 5 or lower. Tulips, daffodils, crocus and other early-spring bulbs planted in the fall survive our winters and bloom beautifully in early spring for many years to come. But other bulbs such as elephant ears, Rex begonias or caladiums must be brought indoors. Any perennial marked Zone 6 or higher must be treated as an annual, protected in our winters. Some higher-zone plants will survive, they just won’t bloom. For more information, see:

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