There are two main systems used to define gardening zones:
1. USDA Plant Hardiness Zones:
* Purpose: This system is the most common and widely used in the United States and Canada. It categorizes regions based on their average annual minimum winter temperatures.
* Number of Zones: There are 13 zones, each representing a 10° Fahrenheit range. Zone 1 is the coldest, and Zone 13 is the warmest.
* Significance: Knowing your USDA hardiness zone helps you choose plants that can survive the winter temperatures in your area.
2. Sunset Climate Zones:
* Purpose: This system is used primarily in California and the western United States. It considers a broader range of climate factors, including humidity, rainfall, and summer temperatures, in addition to winter temperatures.
* Number of Zones: There are 24 zones, each representing a unique combination of climate characteristics.
* Significance: The Sunset Climate Zones offer a more detailed approach than the USDA system, helping gardeners choose plants that thrive in their specific microclimate.
Beyond these two, other zone systems exist:
* AHS Plant Heat Zones: Focuses on the average annual maximum summer temperatures, useful for selecting plants that can withstand heat stress.
* Koppen Climate Classification: A broader climate classification system used globally, with categories like tropical, temperate, and polar.
To find your specific zone:
* USDA: Visit the USDA Plant Hardiness Zone Map: [https://planthardiness.ars.usda.gov/](https://planthardiness.ars.usda.gov/)
* Sunset: Visit the Sunset Climate Zones Map: [https://www.sunset.com/garden/zones/](https://www.sunset.com/garden/zones/)
Important Note: Zone systems are general guides and microclimates within a zone can vary significantly. Factors like elevation, proximity to water, and urban heat islands can affect the actual temperatures in your garden. Always consider these local variations when selecting plants.