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What Are Gardening Zones?

There are two primary classification systems used in the United States to designate gardening zones. Hardiness Zones were created by the USDA and Sunset Climate Zones. Orange County is predominately located in USDA hardiness zone 10a or 10b. However, the hardiness zone classification is based on average low winter temperatures, indicating a plant’s ability to survive winters – something that is rarely experienced by gardeners in Southern California.

A more useful gardening zone index is the 24-zone climate system published in the Sunset Western Garden Book in collaboration with the University of California. Devised in the mid-20th century, the climate zones are geographical regions identified by the sum total of the climate experience: length of the growing season, timing and amount of rainfall, winter lows, summer highs, wind, and humidity. Orange County is predominately located in climate zones 22, 23, and 24. While the Sunset climate zones are much more helpful for gardeners – particularly those in Southern California – I encourage gardeners to start keeping a garden journal which will help identify microclimates even within the same property.

Where can Zone 10b Be Found?

Zone 10 garden areas can be found predominately in Southern California, Florida, and small regions of Arizona, Hawaii, and the very southern border of Texas.

The difference between 10a and 10b gardening zones is a five-degree Fahrenheit increment that vaguely outlines two sub climates within the overall zone. This specification is used to help identify coastal and coastal-inland regions. Coastal growing climates tend to have smaller average temperature swings, providing a more consistent average temperature throughout the growing seasons.

How Growing Zones Can Help You Garden Effectively

Knowing your garden zone is most helpful for setting up your garden. Use it to better understand plant descriptions which are written with USDA hardiness zones in mind, often referencing them on plant tags as well. Knowing your zone can help you with research for the best plants to grow in your zone, whether the plants are annual or perennial options.

The best way to use this collection of data is in tandem with your own garden journal. Your garden journal should refer to your garden zone (USDA or Sunset), but also detail the monthly temperature average for your garden zip code to help you determine the garden season you’re in. Take your garden journal when plant shopping or planning your garden to determine if they’ll be a good fit.

At Heirloom Potager, we help clients develop their gardening knowledge by identifying the garden season as well as their garden zone. Plants can be organized by their preferred growing season, following an arc through the year of weather changes. In Orange County, CA, our garden seasons fall in the following order each year: Cool, warm, hot, warm, and cool again to round out the year. Knowing this arc helps you plan out when and what to plant for the best results. Without a cold period – meaning temperatures fall near or below freezing – many herbaceous perennials from colder regions fail here because the winters are too warm for the required dormancy period. This dormancy period is typically referred to as chill hours.

The zones are a guide and a good starting point, but you still need to determine for yourself what will and won’t work in your garden. Keeping a garden journal will help you can keep personalized notes about your microclimates and the impact of how the plants grow in your garden.