2017-03-19 / News

Understand hardiness zones before planting


USDA Hardiness Zone map courtesy of the USDA. View an interactive version at the USDA website. USDA Hardiness Zone map courtesy of the USDA. View an interactive version at the USDA website. Gardening benefits the environment in myriad ways. Maintaining natural landscapes and preserving green spaces can reduce the collective carbon footprint of the human race. Trees, flowers and other greenery filter the air and create welcoming habitats for all species of animals and insects.

Many home gardeners set out each spring to create landscapes that cater to all of the senses. But choosing plants that are unlikely to thrive in certain climates can lead to dissatisfaction and premature plant demise and may require gardeners to use more fertilizers, pesticides and other not-so-Earth-friendly techniques to help plants thrive.

One of the more important steps gardeners can take before spring arrives is to educate themselves about plant hardiness zones. Hardiness zones are defined by the average climatic conditions of the region and are broken down into various zones. The USDA Hardiness Zone map divides North America into 13 separate zones. Each zone is marked by 10 F incremental differences from the last zone. In some versions of the map, each zone is further divided into “a” and “b” regions.

The National Gardening Association says the USDA Hardiness Zone Map was revised in 2012. The latest version was jointly developed by the USDA’s Agricultural Research Service and Oregon State University’s PRISM Climate Group. To help develop the new map, the USDA and Oregon State University requested that horticultural and climatic experts review the zones in their geographic areas. As a result, the zone boundaries in the 2012 edition of the map have shifted in many areas. Canada’s Hardiness Zone map, updated in 2010, uses nine different zones.

Zone maps are tools that show where permanent landscape plants can adapt. Home gardeners who are looking for shrubs or perennials to last year after year should recognize that such plants must tolerate year-round conditions, including the lowest and highest temperatures and the amount of precipitation. Snow cover and humidity also can impact a plant’s propensity to thrive.

While zone maps are not perfect, they can be useful in planning and ensuring the survival of future gardens. Plant and seed manufacturer Burpee says that other factors to consider that also affect the viability of plants include wind, moisture and soil conditions. The company offers an interactive zone finder on their website that will indicate the hardiness zone as well as average first and last frost dates. Visit www.burpee.com/findgrowzone to enter a zip code.

Learn more about plant hardiness at planthardiness.ars.usda.gov/PHZMWeb. In Canada, visit the site www.planthardiness.gc.ca/?m=1.

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