Successfully cultivating a garden relies heavily on understanding the local climate classifications that determine plant survival. Northeast Pennsylvania, characterized by its diverse topography, does not conform to a single temperature profile, making a definitive single answer for its climate zone impossible. The United States Department of Agriculture (USDA) Plant Hardiness Zone Map provides the necessary framework for local gardeners to determine which perennial plants, trees, and shrubs will survive the winter in their specific location. This system is the primary tool for making informed decisions, ensuring they can withstand the coldest temperatures of the year.
Defining the USDA Plant Hardiness Zone System
The USDA Plant Hardiness Zone Map is a standardized tool developed to help growers select appropriate plants for a given location. The system is based solely on one metric: the average annual minimum winter temperature, which represents the lowest temperature a plant is statistically likely to experience. This map divides North America into 13 zones, with each major zone representing a 10-degree Fahrenheit range of minimum winter temperatures. Lower zone numbers correspond to colder climates; for instance, Zone 5 is colder than Zone 6.
For greater precision, each major zone is split into two 5-degree Fahrenheit sub-zones, designated by the letters ‘a’ and ‘b’. The ‘a’ sub-zone is the colder half of the zone’s temperature range, while ‘b’ is the warmer half, providing a much finer resolution for selecting species. The most recent 2023 map update utilized thirty years of climate data (1991 to 2020) to establish these minimum temperature boundaries.
Specific Hardiness Zones in Northeast PA
Northeast Pennsylvania is situated across a blend of zones, primarily falling within Zones 5b, 6a, and 6b, with a few isolated areas reaching 7a. The most widespread classification across the region is Zone 6a, which indicates an average annual minimum winter temperature range of -10°F to -5°F. This zone covers the majority of the lower-lying valleys and many populated areas, including portions of Wilkes-Barre and Scranton.
Higher-elevation areas and the northernmost sections of the region, such as parts of Susquehanna and Wayne counties, are designated as the colder Zone 5b. This zone experiences average minimum temperatures ranging from -15°F to -10°F. Conversely, the warmest sections, classified as Zone 6b, with a range of -5°F to 0°F, are often found near the Delaware River. The 2023 update resulted in a noticeable shift, with many areas previously categorized as 5b now falling into the warmer 6a category, reflecting long-term temperature trends.
Regional Factors Influencing Local Zone Variations
The broad zone classifications across Northeast PA are fragmented by localized microclimates, which are small areas where the climate differs from the general regional classification. Elevation plays a significant role, as evidenced by the colder Zone 5b areas found in high-altitude regions. For every thousand feet of elevation gain, temperatures generally decrease, pushing these highland areas into a colder classification than the surrounding valley floors.
Proximity to large bodies of water, particularly the Delaware River, often moderates the minimum temperatures in adjacent areas. Water retains heat longer than land, releasing it slowly during the winter and preventing deep cold snaps in the nearby river valleys, which helps explain the presence of Zone 6b in these locations.
Urban centers, such as the concentrated downtown areas of Scranton and Wilkes-Barre, also create the urban heat island effect. Infrastructure absorbs and re-radiates heat, making these city centers a half-zone warmer than the surrounding suburban or rural landscapes. Gardeners must consider their immediate property, as a sheltered location against a south-facing brick wall can create a microclimate that differs substantially from the official zone designation.
Applying Zone Information for Successful Gardening
Once the local hardiness zone is determined, the information becomes a practical guide for selecting perennial plants. The zone number found on a plant tag indicates the coldest climate in which that species is expected to survive the winter. For a resident in Zone 6a, purchasing a plant labeled as “Hardy to Zone 6” means it should reliably survive, while choosing a plant only rated for Zone 7 introduces a significant risk of winter death.
Gardeners in the cooler 5b sub-zone should exercise particular caution and may need to provide additional winter protection for plants rated for Zone 6. It is advisable to select plants rated for the local zone or a colder zone to ensure maximum survivability. While the hardiness zone is a predictive tool for cold tolerance, it does not account for other factors like summer heat, rainfall amounts, or soil drainage, all of which affect a plant’s health. Selecting species that are native or well-adapted to the specific seasonal temperature fluctuations and moisture levels of Northeast PA will further increase the chances of a thriving landscape.