Region defined by minimum temperature relevant to the plant survival

Hardiness zone

Hardiness zone

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 <a href="/en/United_States_Department_of_Agriculture" title="United States Department of Agriculture" class="wl">United States Department of Agriculture</a> (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.

<div class="shortdescription nomobile noexcerpt noprint searchaux" style="display:none" about="#mwt1">Region defined by minimum temperature relevant to the plant survival</div>
<figure class="mw-default-size wiki-thumb"><a href="/en/File:USDAHardiness_2012-2015_Scale.jpg" class="mw-file-description image media-thumb" data-hash="File:USDAHardiness_2012-2015_Scale.jpg"><img loading="lazy"alt="(See table below)" src="//upload.wikimedia.org/wikipedia/commons/thumb/a/a2/USDAHardiness_2012-2015_Scale.jpg/220px-USDAHardiness_2012-2015_Scale.jpg" decoding="async" data-file-width="2550" data-file-height="3300" data-file-type="bitmap" height="285" width="220" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/a/a2/USDAHardiness_2012-2015_Scale.jpg/330px-USDAHardiness_2012-2015_Scale.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/a/a2/USDAHardiness_2012-2015_Scale.jpg/440px-USDAHardiness_2012-2015_Scale.jpg 2x"></a><figcaption>Temperature scale used to define USDA hardiness zones. These are annual extreme minima (an area is assigned to a zone by taking the lowest temperature recorded there in a given year). As shown, the USDA uses a GIS dataset averaged over 1976 to 2005 for its United States maps.</figcaption></figure>
<figure class="mw-halign-right wiki-thumb"><a href="/en/File:World_Hardiness_Zones.png" class="mw-file-description image media-thumb" data-hash="File:World_Hardiness_Zones.png"><img loading="lazy" src="//upload.wikimedia.org/wikipedia/commons/thumb/a/a7/World_Hardiness_Zones.png/290px-World_Hardiness_Zones.png" decoding="async" data-file-width="2729" data-file-height="2213" data-file-type="bitmap" height="235" width="290" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/a/a7/World_Hardiness_Zones.png/435px-World_Hardiness_Zones.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/a/a7/World_Hardiness_Zones.png/580px-World_Hardiness_Zones.png 2x" alt="World_Hardiness_Zones.png"></a><figcaption>Global Plant Hardiness Zones (approximate)</figcaption></figure>

Unless otherwise specified, in American contexts "hardiness zone" or simply "zone" usually refers to the USDA scale. For example, a plant may be described as "hardy to zone 10": this means that the plant can withstand a minimum temperature of 30&nbsp;°F (−1.1&nbsp;°C) to 40&nbsp;°F (4.4&nbsp;°C).

Other hardiness rating schemes have been developed as well, such as the UK <a href="/en/Royal_Horticultural_Society" title="Royal Horticultural Society" class="wl">Royal Horticultural Society</a> and US Sunset Western Garden Book systems. A heat zone (see below) is instead defined by annual high temperatures; the <a href="/en/American_Horticultural_Society" title="American Horticultural Society" class="wl">American Horticultural Society</a> (AHS) heat zones use the average number of days per year when the temperature exceeds 30&nbsp;°C (86&nbsp;°F).

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 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 in various forms. Unless otherwise specified, in American contexts "hardiness zone" or simply "zone" usually refers to the USDA scale. For example, a plant may be described as "hardy to zone 10": this means that the plant can withstand a minimum temperature of 30 °F to 40 °F . 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 is instead defined by annual high temperatures; the American Horticultural Society heat zones use the average number of days per year when the temperature exceeds 30 °C . 