Climate Zone (Aka Hardiness Zone)
We in the horticultural industry talk a lot about climate zones, but do you really know what a climate zone is? Do you know your climate zone? Wikipedia describes climate/hardiness zones as “geographically defined area in which a specific category of plant life is capable of growing.” The two most commonly used climate zones are the United States Department of Agriculture (USDA) Plant Hardiness Zones and the Sunset Western Climate Zones.
The USDA Plant Hardiness Zones are divided into 10 degree Fahrenheit zones. These zones give a rough guide to landscaping and gardening. Although this guide is informative; taking into consideration the extremes of winter cold, and if a particular plant species can be grown outside in a particular location, these zones do not incorporate summer heat into the zone determinations. The Central Coast of California, from Paso Robles to Santa Barbara, has a USDA Hardiness Zone range from 8a to 10a, with the California Central Valley being in zones 9a and 9b.
The Sunset Western Climate Zones are based on a “broad range of factors such as cold, heat, humidity, winds, proximity to the Pacific Ocean, snow cover and length of growing season.” (The New Sunset Western Garden Book, 2012, p. 17). This broad spectrum of conditions provides western gardeners and landscapers a very detailed picture of what plants will thrive in their gardens and which plants are better suited elsewhere. When doing research on plants, we choose to focus on Sunset Western Climate Zones. Below is a brief list of climate zones in our local communities:
North Coast: (Los Osos, Morro Bay, Cayucos, Cambria) Zones 15-17
North San Luis Obispo County: (Santa Margarita, Atascadero, Templeton, Paso Robles, San Miguel) Zone 7
San Luis Obispo: Zones 14-17
South Coast: (Avila Beach, Shell Beach, Pismo Beach, Grover Beach, Arroyo Grande, Oceano, Nipomo) Zones 14-16
Santa Maria Valley: (Guadalupe, Santa Maria, Orcutt, Lompoc) Zones 14-17
Santa Ynez Valley: (Buelton, Los Olivos, Solvang, Santa Ynez) Zones 7-8 & 14-17
Santa Barbara: (Goleta, Santa Barbara, Montecito, Carpinteria, Ventura, Oxnard) Zones 21-24
Central Valley: (Hanford, Tulare, Visalia, Kingsburg, Fresno, Clovis, Madera) Zones 8-9
Keeping all of this information in mind, it is important to also consider the impact Microclimates can have on how plants perform in the landscape. A Microclimate can be described as the climate of a small area, as large as a neighborhood or as small as a corner of the garden, that differs in temperature from the climate of the surrounding area. Examples of this could be in heavy urban areas where large areas of concrete and asphalt absorb the sun’s heat, resulting in a heat island. Another would be deeply shaded areas that stay cool even in hot summer regions. One more example would be an area on the south side of a building that is in shade during the summer and full sun in the fall and winter.
Knowing your climate zone will help to ensure many years of successful gardening. Detailed information about each of the zones listed above can be found in The New Sunset Western Garden Book or online at www.sunset.com. Lastly, the saying “Right Plant, Right Place” is vitally important, and your local independent retail nurseries and Landscape professionals are the people to reach out to help design a landscape that will thrive in your area.