Perennial plant survival is determined by the lowest temperatures they can tolerate. Categorizing geographical areas based on climate ensures planting success in agriculture and horticulture. These classifications guide growers on which trees, shrubs, and flowers are most likely to thrive over multiple seasons in a specific location.
Kansas’s Primary Zone Classification: USDA Hardiness
Kansas encompasses a range of USDA Hardiness zones due to its expansive geographic area and varied conditions. The state stretches from the high plains in the west to the more temperate Ozark foothills in the southeast, creating a wide thermal gradient. Based on the 2023 update, Kansas zones primarily span from \(5\text{b}\) to \(7\text{a}\).
The coldest pockets (\(5\text{b}\)) are found in the far northwest corner. The majority of the state falls within zones \(6\text{a}\) and \(6\text{b}\), including central regions. Warmer sections, such as Wichita and the southeast corner near Pittsburg, are classified as the warmest zone, \(7\text{a}\).
Interpreting the Hardiness Zone System
The official system measures a region’s winter cold tolerance based on the average annual minimum winter temperature recorded over a 30-year period (1991 to 2020 for the latest map). Each full zone number represents a \(10^\circ \text{F}\) temperature band defining the average lowest temperature experienced. For example, a plant rated for Zone 6 can withstand a minimum temperature \(10^\circ \text{F}\) warmer than a plant rated for Zone 5.
To provide greater precision, each main zone is divided into two subzones, labeled ‘a’ and ‘b’. Each subzone represents a \(5^\circ \text{F}\) temperature increment. The ‘a’ designation represents the colder half of the range, while ‘b’ represents the warmer half.
Practical Application for Kansas Gardeners
Knowing the specific classification is primary for plant selection. Gardeners should select perennial plants rated for their specific zone or a lower, colder number. Choosing a plant rated for a colder zone, such as Zone 5 in a Zone 6 location, adds a buffer against unusual cold snaps.
Localized conditions, known as microclimates, can also affect plant survival. Features like concrete driveways or brick walls create “urban heat islands” that warm an area, while low-lying areas can become colder pockets. The hardiness classification only addresses winter cold, so Kansas gardeners must also consider the American Horticultural Society (AHS) Heat Zone. This separate system accounts for the number of days the temperature exceeds \(86^\circ \text{F}\), which impacts plant stress and survival during hot Kansas summers.