The success of a perennial garden in Arkansas begins with understanding its local climate, particularly its winter temperatures. The United States Department of Agriculture (USDA) Plant Hardiness Zone (PHZ) map is the standard reference for gardeners, dividing North America into zones that indicate where a plant is most likely to survive the winter season. Because Arkansas features varied geography—from the mountainous Ozarks to the flat Gulf Coastal Plain—it spans multiple hardiness zones. Selecting plants based on this zone information is the first step in ensuring long-term survival for trees, shrubs, and other perennial plantings.
Decoding the Plant Hardiness Zone System
The USDA Plant Hardiness Zone system is a classification tool based on a single, specific climate metric. Zones are defined by the average annual extreme minimum winter temperature recorded over a 30-year period, with the most recent map update covering the years 1991 to 2020. This particular measurement is the most telling factor for determining if a perennial plant can survive the coldest point of the year in a given region.
The map is divided into 13 zones, each representing a 10-degree Fahrenheit difference in the average minimum winter temperature. To provide greater precision, each zone is further split into ‘a’ and ‘b’ sub-zones, which represent a finer 5-degree Fahrenheit variation. For example, Zone 7b is 5 degrees warmer than Zone 7a. This system is crucial because a plant’s ability to withstand the lowest temperature it will face is the primary factor determining its survival through the winter.
The Specific Hardiness Zones of Arkansas
Arkansas is no longer confined to a single hardiness number, with the state now spanning USDA zones 7a through 8b, reflecting a slight warming trend over time. The coldest areas, generally designated as Zone 7a, are found in the higher elevations of the Ozark and Ouachita Mountains in the northern and western parts of the state. These regions experience average annual minimum temperatures between 0°F and 5°F.
The majority of central Arkansas, including the Arkansas River Valley and metropolitan areas like Little Rock, falls into Zone 7b. This dominant zone has an average minimum temperature range of 5°F to 10°F, allowing for a broader selection of perennial plants. Gardeners here can successfully grow plants like Southern Magnolia and certain varieties of Crape Myrtle.
The warmest zones, 8a and even some pockets of 8b, are situated in the far south and southeastern counties, particularly in the Gulf Coastal Plain region. Zone 8a registers minimum temperatures between 10°F and 15°F. This allows gardeners in places like Pine Bluff and Texarkana to cultivate slightly more cold-sensitive plants, such as certain palms or camellias. Because the state’s topography and proximity to major rivers create distinct microclimates, gardeners must verify the specific zone for their county or address rather than relying on a single statewide number.
Essential Considerations Beyond Winter Tolerance
While the Plant Hardiness Zone map is an excellent tool for predicting winter survival, successful gardening in Arkansas requires considering other environmental factors. The American Horticultural Society (AHS) Heat Zone Map offers a necessary complement to the USDA map by addressing summer intensity. This system defines zones based on the average number of days per year that temperatures exceed 86°F (30°C), a point where many plants begin to experience physiological stress.
Arkansas, being a state with hot, humid summers, often falls into higher AHS Heat Zones, meaning plants must be able to tolerate extended periods of high heat. Gardeners also need to account for localized microclimates that can alter the effective zone of a small area. For instance, a plant situated against a south-facing brick wall or tucked into an urban area will experience warmer temperatures than one in an open field.
Soil composition is another variable, as Arkansas boasts a diverse range of soil types, from rocky, gravelly soils in the mountains to clay-heavy alluvial soils in the Delta. Many of the state’s soils tend to be acidic, and the expansive nature of clay-rich soils in the eastern and southern regions can lead to poor drainage. Understanding the native soil—and amending it to ensure proper water retention and drainage—is important for plant survival.