Spring is the season for planting and envisioning new garden and yard landscapes. Garden centers are full of attractive flowers, shrubs and trees. When selecting perennial varieties that will survive through winters in South Dakota, use the U.S. Department of Agriculture (USDA) Plant Hardiness Zones to help identify the best candidates for your landscape.
The USDA Plant Hardiness Zones (PHZ) were updated in 2012. For many years, gardeners and landscapers may have used the Sunset hardiness zones, which were last updated in 1990. These are similar and were printed on seed packets and made popular through Sunset magazine and their associated gardening publications. The Sunset zones used much-older climate data; however, and thus, the USDA updated the maps to reflect more-recent wintertime temperatures.
The 2012 PHZ maps use the same calculation as the old Sunset zones. The calculation uses the average annual extreme minimum temperature for the years 1976–2005. This serves to identify thresholds of pests, diseases and plant damage due to cold temperatures. In South Dakota, over the last several decades, there has been a trend of warmer winter temperatures. As a result, many areas of South Dakota are now categorized in a higher number zone. Much of the state moved one zone warmer, for example from 4a to 4b, or 4b to 5a. Zone 4 indicates average annual extreme minimum temperatures of -30 degrees Fahrenheit to -20 degrees Fahrenheit. The USDA website has a feature where you can search by ZIP code to find your local plant hardiness zone.
Your local yard or garden may be warmer or colder than what the PHZ map shows, but it serves as a good starting point when selecting plants for your area. Labels on perennial plants, trees and seed packets will often indicate the appropriate climate zone or plant hardiness zone for that variety. You should always look for this information and purchase plants that are appropriate for your zone. Local nurseries and garden centers will likely not sell varieties that won’t overwinter well in our climate, but you should take note if you purchase from a national chain store or bring in plants from elsewhere, especially from the south, where they have less extreme-cold winter temperatures. While plant survival from year to year is never 100% guaranteed, selecting plants from the appropriate hardiness zone will give you the greatest chance for success in keeping your favorite plants in the garden for many years.