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 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. A plant may be described as "hardy to zone 10": this means that the plant can withstand a minimum temperature of −1.1 to 4.4 °C (30 to 40 °F).

Unless otherwise specified, in American contexts "hardiness zone" or simply "zone" usually refers to the USDA scale. However, some confusion can exist in discussing buildings and HVAC, where "climate zone" can refer to the International Energy Conservation Code zones, where Zone 1 is warm and Zone 8 is cold.

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).

A hardiness or heat zone are both highly specific with respect to altitude, amount of sunlight, rainfall, humidity levels, wind chill, wind speed, amongst other conditions, regardless of latitude and longitude. Trees and greenery foliage may provide dappled or full shade like they can break wind to provide, as do greenhouses without artificial climate control. As a result, microclimates are created where some plants may unexpectedly thrive. Always include caution, knowledge from personal experiences and trial and error when determining whether a plant will grow or not in a particular area.https://evergreenbotany.com/blogs/news/plant-growing-zones