Hardiness zones, while commonly used in gardening, are not the best criteria for selecting native plants. These zones are based solely on average minimum winter temperatures over a 30-year period, which helps determine whether a plant will survive in a given area. However, this approach overlooks other crucial environmental factors such as soil composition, moisture levels, and regional ecology. As a result, plants selected using hardiness zones alone may not thrive as well as those chosen based on their native ecoregion.
Ecoregions provide a more comprehensive framework for selecting native plants. These regions consider not just temperature, but also climate, soil type, moisture levels, and topography. Plants that have evolved within their native ecoregion over thousands of years develop unique genetic adaptations, often referred to as local genotype, which enable them to thrive in specific conditions. By prioritizing ecoregions rather than hardiness zones, gardeners can better support biodiversity and ecological health.
Relying on hardiness zones can also contribute to the spread of invasive plants. Because these zones focus only on temperature tolerance, they do not take into account whether a plant has the potential to outcompete native species. Many invasive species thrive in a wide range of conditions and, when introduced outside their native range based on hardiness zone suitability, can spread aggressively. This disrupts local ecosystems, reduces biodiversity, and threatens native plants and wildlife. By selecting plants based on ecoregions rather than hardiness zones, gardeners can avoid inadvertently introducing species that may become invasive and instead support the health and resilience of local habitats.