What You Need to Know About Iowa’s Plant Zone

Iowa Map

Iowa gardeners and plant enthusiasts now have access to an updated plant hardiness zone map. The U.S. Department of Agriculture (USDA) has recently released an updated version of the map, the first update since 1990. This latest edition reveals that much of Iowa is now considered Zone 5. But what does this mean for gardeners and the plants they choose?

Understanding Plant Hardiness Zones

Plant hardiness zones are important tools for gardeners and researchers alike. These zones represent the average annual minimum temperatures at a particular location. The new USDA map divides the United States into 13 zones, two more than the previous version. The data used to determine these zones was measured during the 30-year period from 1976 to 2005. Each zone is a 10-degree Fahrenheit band, further divided into A and B 5-degree Fahrenheit subzones. For example, Zone 5 has an average annual minimum temperature range of -10 to -20 degrees Fahrenheit.

Shifts in Zone Boundaries

Compared to the 1990 version, the new map exhibits significant shifts in zone boundaries. Overall, the zones have moved northward across the country. Jennifer Bousselot, Iowa State University (ISU) Extension horticulturist and Iowa Master Gardener coordinator, states that locations on the new map are generally five degrees Fahrenheit warmer than those on the previous map. While this half-zone difference may not seem substantial, it is still important for Iowa gardeners to take into account.

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Factors Influencing Zone Changes

The changes in the zone boundaries are the result of improved mapping methods. The new USDA map incorporates algorithms that consider factors such as changes in elevation, proximity to large bodies of water, and topographical features like valley bottoms and ridge tops. Richard Jauron, ISU Extension horticulturist, reminds gardeners to use the zone map as a guide and to consider their specific location details when selecting plants.

Local Influences on Plant Selection

Jauron emphasizes the need for gardeners to factor in local variations when choosing plants. For instance, it would be incorrect to assume that the same plants can thrive in both Mason City and Ames simply because both cities are located in Zone 5a. Mason City tends to experience several degrees colder temperatures than Ames during winter. It is essential to consider differences between rural and urban areas, low-lying regions near streams, and elevated hilltops. These local factors can significantly impact temperature variations.

Planting Recommendations for Northern Iowa

Jauron advises caution for gardeners living north of Highway 20. While they may experiment with a few plants labeled as hardy in Zone 5a, the most reliable choices for this region are still Zone 4 plants. It is crucial to select plants that can withstand the colder temperatures and climate conditions prevalent in northern Iowa.

Accessing the USDA Plant Hardiness Zone Map

To assist gardeners in making informed decisions, the USDA map is available in an interactive format online. By using the “find your zone by ZIP code” function, users can easily determine their specific hardiness zone. This new map is a joint effort between USDA’s Agricultural Research Service (ARS) and Oregon State University’s (OSU) PRISM Climate Group. Its aim is to provide gardeners with accurate and detailed information for their planting choices.

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For a wide range of plants that are suitable for Iowa’s climate and hardiness zones, visit the Ames Farm Center. With the updated plant hardiness zone map, gardeners can confidently select plants that will thrive in their specific Iowa location. Happy gardening!