Gardeners rely on the standardized USDA Plant Hardiness Zone Map to determine which perennial plants can survive winter temperatures in a specific location. This map divides North America into zones based on long-term weather data. Knowing your zone is fundamental for successful gardening, as it dictates the minimum cold tolerance a plant must possess to thrive outdoors year after year. Due to its unique geographic position, Long Island, New York, falls into zones that are generally warmer than much of the rest of New York State.
Defining the Long Island Hardiness Zone
Long Island is primarily situated within USDA Plant Hardiness Zones 7a and 7b, making it one of the warmest areas in New York State for plant survival. Zone 7a is the colder of the two, with average annual minimum winter temperatures ranging from 0°F to 5°F. The warmer 7b zone experiences average annual minimum winter temperatures between 5°F and 10°F. The majority of the island, including Nassau County and most of Suffolk County, is designated as the milder Zone 7b. Zone 7a is generally found in isolated sections of eastern Suffolk County, such as areas around Riverhead, East Quogue, and parts of the South Fork.
How the Hardiness System Works
The USDA Plant Hardiness Zone Map is the standard tool used to guide the selection of perennial plants for a specific location. The system is based solely on the average annual extreme minimum winter temperature recorded over a 30-year period. It is important to recognize that this is an average of the coldest night of the year, not the lowest temperature ever recorded in that location. The map is divided into 13 major zones, with each zone representing a 10°F range of minimum temperature. Each zone is further subdivided into “a” and “b” sections, which represent 5°F increments, with “a” being the colder half.
Localized Zone Variations Across Long Island
The specific zones across Long Island are heavily influenced by geographic features that create distinct microclimates. The most significant factor is the maritime effect, which is the moderating influence of the Atlantic Ocean and Long Island Sound. These large bodies of water warm and cool more slowly than land, resulting in milder winter temperatures along the coastline. Coastal areas are often classified as the warmer 7b zone, while locations further inland, particularly in eastern Suffolk County away from the immediate shorelines, are more likely to fall into the colder 7a zone. Furthermore, highly developed areas like western Nassau County can experience the urban heat island effect, where concrete and buildings absorb and re-radiate heat, making these developed zones comparatively warmer than surrounding rural or suburban areas.
Using Your Zone for Successful Planting
The primary purpose of knowing your hardiness zone is to select perennial plants, shrubs, and trees that can successfully survive the winter minimum temperatures. A plant rated for Zone 7, for instance, is expected to endure the average minimum temperature range of 0°F to 10°F. Selecting plants rated for a lower zone, such as Zone 6, provides a greater margin of safety against unusually cold winters. The hardiness zone is not a measure of summer heat, frost dates, or other local conditions, and annual plants are not dependent on the hardiness zone. Gardeners must also consider their specific microclimate, such as wind exposure, sun intensity, and proximity to buildings, which can slightly alter the effective zone for a plant. A plant placed against a south-facing brick wall, for example, will be in a warmer spot than the official zone designation suggests.