All of Long Island is located within the USDA Plant Hardiness Zones 7a and 7b, which experience annual average minimum temperatures of 0 to 10 F.
With the exception of Montauk on the eastern border and a portion of Bay Shore on the western border, Suffolk County is almost entirely classified as USDA Zone 7a while Nassau County, with the exception of Hicksville and most of the northeastern portion of the county, is classified as USDA Zone 7b.
If you are planning on gardening in your backyard in Nassau or Suffolk County on Long Island, New York, please note that many seed catalogs, gardening magazines, books, and nurseries will tell you in which zones each of the various plants can grow successfully.
While all locations within Long Island fall in Zones 7a and 7b, it's a good idea to double-check your home address by entering your zip code into the National Gardening Association's USDA Hardiness Zone Finder.
Plant Hardiness Zone Maps and Tools
Gardeners know that not every plant, flower or tree will thrive in every climate. To make the job of deciding what to plant easier, the United States Department of Agriculture (USDA) created a map of the United States and gave a number and letter to different geographical areas according to their average annual minimum temperatures.
These areas, called hardiness zones, are each separated by 10 degrees Fahrenheit and range from zone 1a, which has an average minimum temperature of -60 to -55 F and goes up to zone 13b, where the average minimum temperature ranges between 65 to 70 F.
An earlier version of the USDA's Plant Hardiness Zone Map, created in 1960 and still current in 1990, showed 11 different zones in the U.S. Then in 2012, the United States Department of Agriculture created a new Plant Hardiness Zone Map, which further divided the zones from 10-degree ranges to five-degree ranges.
In addition to the USDA map, the National Arbor Day Foundation created its own Plant Hardiness Zone Map in 2006, basing their renderings on data gleaned from 5,000 National Climatic Data Center stations across the country. You can download a high-resolution version of the map on the Arbor Day Foundation website and zoom in to Long Island or check your home's specific zone by using their zone lookup tool.
Other Factors That Affect Plant Hardiness
Some gardeners would argue that you can't rely solely on the temperatures in an area to gauge how likely a plant is to survive. There are other climatic variables to take into account including the amount of rainfall in a given season, the humidity in an area, and the summer heat.
Additionally, a winter where the snow covers the ground and many plants may have a beneficial effect, and soil drainage or lack thereof is also another critical factor in whether a specific type of plant survives in any given area.
As a result, some Long Islanders would advise buying plants that are in Zone 6—which is colder than the "official" Long Island Zone 7—just in case an extremely cold winter happens. That way, they believe, these hardier plants will make it through the freezing weather no matter what happens.