Understanding the local climate, especially extreme temperatures, is vital for garden success. The United States Department of Agriculture (USDA) developed the Plant Hardiness Zone Map to help gardeners assess a plant’s ability to survive winter. Kansas, a geographically large state, spans several hardiness zones rather than falling under a single designation. Knowing the precise zone is the first step in selecting perennial plants, trees, and shrubs that will thrive.
Understanding the USDA Hardiness Zone Map
The USDA Plant Hardiness Zone Map is the standard reference for determining a perennial plant’s cold tolerance. The map divides North America into 13 zones based solely on the average annual extreme minimum winter temperature recorded over a 30-year period. Each full zone represents a 10-degree Fahrenheit difference in the average coldest temperature of the year.
For greater precision, each zone is further divided into “a” and “b” sub-zones, denoting a finer 5-degree Fahrenheit increment. For example, Zone 6a is five degrees colder than Zone 6b. This detailed system allows gardeners and nurseries to communicate the cold resilience of plants accurately.
The Diverse Zone Range of Kansas
Kansas covers a significant range of cold hardiness zones, reflecting the state’s continental climate and north-to-south geography. The most recent map update (1991 to 2020 data) places the state predominantly within Zones 5b, 6a, 6b, and 7a. This variation means planting strategies differ considerably across the state.
The coldest areas are found in the far northwest corner of Kansas, classified as Zone 5b (average minimum temperatures between -15°F and -10°F). Central Kansas is typically in the 6a and 6b zones. This progression reflects increasing warmth further south and east.
The warmest zones are located in the south-central and southeastern regions, including areas around Wichita and Pittsburg, designated as Zone 7a. Zone 7a has an average annual minimum temperature range of 0°F to 5°F. This geographical progression from colder to warmer zones across the state helps identify which plants will survive the winter.
Pinpointing Your Specific Zone and Selecting Plants
A general map is not sufficient to determine the specific zone for a home garden due to the localized nature of the zones. The most accurate method is to use the interactive USDA Plant Hardiness Zone Map online and search by address or zip code. This tool provides the precise zone designation, including the “a” or “b” subdivision.
The zone number serves as a direct guide for selecting perennial plants, trees, and shrubs. A plant labeled “hardy to Zone 6” is expected to survive the average minimum winter temperatures in Zone 6 and any warmer zone (e.g., Zone 7). Gardeners should choose plants rated for their local zone or any lower-numbered zone, which indicates greater cold tolerance.
For instance, a gardener in Zone 6b should select plants rated for Zone 6b or colder zones like 6a or 5. Choosing a plant rated only for Zone 7a means it is likely to perish during a typical 6b winter. This selection process ensures the plant’s cold hardiness aligns with the coldest weather it is likely to face. The zone designation is most important for plants that remain outdoors throughout the year, unlike annual flowers or vegetables grown during the frost-free season.
Considering Heat Zones and Microclimates
While the USDA map focuses on winter cold, the American Horticultural Society (AHS) developed the Plant Heat-Zone Map to address summer heat, another significant factor in plant survival. This map divides the country into 12 zones based on the average number of “heat days” per year. A heat day is defined as a day where the temperature exceeds 86°F (30°C), the point at which many plants begin to experience stress.
Gardeners should consider both the cold hardiness zone and the heat zone when selecting plants to ensure survival through both winter and summer extremes. Microclimates are localized areas within a garden that have different conditions than the surrounding environment. Factors like proximity to a south-facing brick wall, a large body of water, or a change in elevation can create pockets that are slightly warmer or colder than the official USDA zone.
A sheltered location next to a building that absorbs and radiates heat, for example, can create a warmer microclimate. This may allow a gardener to successfully grow a plant rated for half a zone warmer than their official designation. Conversely, a low-lying valley where cold air settles can effectively make a spot half a zone colder. Recognizing these localized variations allows for minor adjustments to planting strategy.