Below are links to PHZM data in three formats. The shapefiles represent the half-zone classifications in a format suitable for mapping software. The grid files provide the average annual minimum winter temperature values on which the zones are based, giving the type of sub-zonal precision needed for scientific usage. There is also a listing of plant hardiness zones and half zones by ZIP code. Metadata describing the files is included with each format.
Cold-hardiness is not a factor for plants in Zone 11 because there is no frost. Instead, you might want to look up a Heat Zone Map. It divides the country into 12 zones based on the number of days wherein the temperature goes above 86°F in each region.
There's an Open Plant Hardiness Zones (OPHZ) project on Github where various people have reverse-engineered a pdf of the hardiness zones (pdf, really large) to produce a GIS file (SHP) of the zone boundaries. The ophz-c version is the latest. It's public domain.
One of the most important things cold-climate gardeners need to know is their plant hardiness zone. Cold hardiness zones are established by the U.S. Department of Agriculture every 20 years or so. The lower your zone number, the colder it is.
USDA Plant Hardiness Zones can be used to predict which plants will survive in a garden. There are actually 13 Plant Hardiness Zones. Plant hardiness zones are primarily used to determine how many days your plants will be frost-free. Still, they can also determine how far south you can grow certain plants.
Plant hardiness, as defined by the USDA, refers to the hardiness of a particular species to tolerate average extreme winter low temperatures. Winter temperature data for the 2012 map was collected from thousands of weather stations all over the country over a period of thirty years. This data, as well as other factors, such as elevation and proximity to a large body of water, were used to set plant hardiness zones for all areas of the country.
Using the South Carolina USDA plant hardiness map as a guide is a good idea when choosing plants for this region. Click on the map above to enlarge it and locate your growing zone. If you have a difficult time finding your zone, you can go to the USDA site where you can input your zip code. The western part of the state is the coolest while the southeast enjoys a very temperate winter climate. South Carolina zones include 5b through 8b.
Planting zones can vary in your region. Some states can have two or more hardiness zones in their state alone. As a result, you will have different temperatures and planting times. However, they all have to face specific weather typical to their area.
As an illustration, kale is a vegetable that grows in all zones, but you can grow it as perennials if you live in zones 7 and up. Consequently, you can have kale all year long. What else can you grow based on the plant hardiness zones map?
If you'd like to view the zone for your area, you can use the USDA's interactive map to find the plant hardiness zone in your exact location, down to the ZIP code. Remember, hardiness zones can differ across town. A heat island effect in downtown areas might warrant a warmer zone than a less-populated suburban area. Elevation change can affect average temperatures, too.
Planting zones set the guidelines to help gardeners understand the conditions of where their gardens grow. Each plant type has its own designated hardiness zone, indicating that the plant is tolerant to the lowest temperatures in that area. Planting outside the zone may result in your plant being shocked by heat or cold. Therefore, understanding categorization can help you select and care for the best permanent landscaping trees, shrubs and perennials for your location.
Separated by 10-degree differences, hardiness zones run from the lowest to highest possible cold conditions. Vegetation with the lowest numbers can withstand the chilliest weather, while higher numbers mean warmer climates are a better match. If a plant belongs to hardiness zones three to seven, this means it's hardy enough to survive some cold, but not enough to endure extreme and prolonged icy periods. On the other hand, a three to seven zone plant needs a certain amount of cold and will likely perish in the desert heat.
The zones are determined by the U.S. Department of Agriculture, working with Oregon State University's PRISM Climate Group, and based on a 30-year period of averaged minimum low temperatures. The latest hardiness map came out in 2012 and is from data collected during the years 1976-2005. Zones are ranked from 1 (-60 degrees) to 13 (70 degrees), though the extremes are rare. To find yours, put in your ZIP code and your hardiness zone will appear
A hardiness zone is a geographic area defined as having a certain average annual minimum temperature, a factor relevant to the survival of many plants. In some systems other statistics are included in the calculations. The original and most widely used system, developed by the United States Department of Agriculture (USDA) as a rough guide for landscaping and gardening, defines 13 zones by long-term average annual extreme minimum temperatures. It has been adapted by and to other countries (such as Canada) in various forms.
Other hardiness rating schemes have been developed as well, such as the UK Royal Horticultural Society and US Sunset Western Garden Book systems. A heat zone (see below) is instead defined by annual high temperatures; the American Horticultural Society (AHS) heat zones use the average number of days per year when the temperature exceeds 30 °C (86 °F).
In the United States, most of the warmer zones (zones 9, 10, and 11) are located in the deep southern half of the country and on the southern coastal margins. Higher zones can be found in Hawaii (up to 12) and Puerto Rico (up to 13). The southern middle portion of the mainland and central coastal areas are in the middle zones (zones 8, 7, and 6). The far northern portion on the central interior of the mainland have some of the coldest zones (zones 5, 4, and small area of zone 3) and often have much less consistent range of temperatures in winter due to being more continental, especially further west with higher diurnal temperature variations, and thus the zone map has its limitations in these areas. Lower zones can be found in Alaska (down to 1). The low latitude and often stable weather in Florida, the Gulf Coast, and southern Arizona and California, are responsible for the rarity of episodes of severe cold relative to normal in those areas. The warmest zone in the 48 contiguous states is the Florida Keys (11b) and the coldest is in north-central Minnesota (2b). A couple of locations on the northern coast of Puerto Rico have the warmest hardiness zone in the United States at 13b. Conversely, isolated inland areas of Alaska have the coldest hardiness zone in the United States at 1a.
In 2006, the Arbor Day Foundation released an update of U.S. hardiness zones, using mostly the same data as the AHS. It revised hardiness zones, reflecting generally warmer recent temperatures in many parts of the country, and appeared similar to the AHS 2003 draft. The Foundation also did away with the more detailed a/b half-zone delineations.
The hardiness scales do not take into account the reliability of snow cover in the colder zones. Snow acts as an insulator against extreme cold, protecting the root system of hibernating plants. If the snow cover is reliable, the actual temperature to which the roots are exposed will not be as low as the hardiness zone number would indicate. As an example, Quebec City in Canada is located in zone 4, but can rely on a significant snow cover every year, making it possible to cultivate plants normally rated for zones 5 or 6. But, in Montreal, located to the southwest in zone 5, it is sometimes difficult to cultivate plants adapted to the zone because of the unreliable snow cover.
Owing to the moderating effect of the North Atlantic Current on the Irish and British temperate maritime climate, Britain, and Ireland even more so, have milder winters than their northerly position would otherwise afford. This means that the USDA hardiness zones relevant to Britain and Ireland are quite high, from 7 to 10, as shown below.
Macaronesia consists of four archipelagos: The Azores, the Canary Islands, Cape Verde and Madeira. At lower altitudes and coastal areas, the Portuguese Azores and Madeira belong to zones 11a/11b and 11b/12a respectively. The Azores range from 9a to 11b and Madeira ranges from 9b to 12a, 9a and 9b found inland on the highest altitudes such as the Mount Pico in the Azores or Pico Ruivo in Madeira. The Spanish Canary Islands hardiness zones range from 8a to 12b depending on the location and the altitude. The islands are generally part of zones 11b/12a in lower altitudes and coastal areas, reaching up to 12b in populated coastal parts such as the city of Las Palmas. The lowest hardiness areas are found in Teide National Park being at 8a/8b for its very high altitude. The Teide peak is the highest peak of Macaronesia. The Cape Verde islands, inside the Tropics, have hardiness zones that range from 12 to 13 in the coastal areas, while the lowest hardiness zone is found in the island of Fogo, in the country's highest peak Pico do Fogo.
The USDA map published in 2012 shows that most of the US has become a half zone (2.8 °C or 5 °F) hotter in winter compared to the 1990 release. Research in 2016 suggests that USDA plant hardiness zones will shift even further northward under climate change.
Hardiness zone maps are not very detailed and do not accurately show hardiness zones in much of the West due to elevation and microclimate variations. The table below includes hardiness zones using the USDA temperature ranges but calculated with local weather data gathered from 1990 to 2019. Hardiness zones are included for most weather stations in Utah and for several stations in each of the surrounding states. The data was provided by Utah Climate Center at Utah State University and calculations were done by Gabrielle Harden, Forestry Extension. To find your zone, find a station near you that is similar in elevation and other factors. A station designation like Telluride 4WNW indicates that the station is located 4 miles west-northwest of Telluride, Colorado. 2b1af7f3a8