The San Fernando Valley, in the north metropolitan Los Angeles, California area, is in U.S. Department of Agriculture zones 10a and 10b. Most peonies, including the popular garden peony (Paeonia lactiflora) and the tree peony (Paeonia suffruticosa), prefer cooler climates. Generally, USDA zone 8b is the warmest environment in which they can grow. However, by making special efforts to choose the right sites and cultural techniques, some peonies may not only survive, but also thrive in southern California.
Peonies will only flower if the crowns and roots are exposed to a certain amount of winter chill. This varies according to species and variety, but in general, peonies need 100 to 300 hours of chilling time each winter. "Chill" means temperatures around 32 degrees Fahrenheit. According to the USDA, average minimum winter temperatures in the San Fernando Valley range from 30 to 35 degrees Fahrenheit, so in any given year, it is likely that peonies will receive some chilling time, but that time amount may or may not be optimum.
Pushing the Zone
"Pushing the zone" means growing plants in USDA plant hardiness zones outside those recommended for specific species. To push the zone for peonies, start with sun-loving types, such as garden peonies (Paeonia lactiflora), hardy in USDA zones 3 through 8; or intersectional (Itoh) peonies, such as "Pink Double Dandy" KEIKO (Paeonia "Pink Double Dandy KEIKO"), hardy in USDA zones 4 through 8. Plant in well-drained soil in an eastward-facing location with morning sun and afternoon shade. Water regularly and provide 2 inches of mulch in the summer. Remove the mulch in the fall so the peony crowns will receive necessary winter chilling.
Search catalogs and websites for peonies that require relatively fewer hours of chilling time within the 100 to 300 hour range. Single or double-flowered varieties generally succeed better than other types in places like the San Fernando Valley. Older varieties -- even some with many petals -- have a history of success in warmer climates. These include white-flowered "Festiva Maxima" (Paeonia "Festiva Maxima"), pink "Baroness Schroeder" (Paeonia "Baroness Schroeder"), and dark pink "Felix Crouse" (Paeonia "Felix Crouse"), all hardy in USDA zones 3 through 8.
Gardeners in the San Fernando Valley should be prepared to experiment to find peony species and varieties that will grow well in the warm southern California climate. Many properties, especially large ones, also contain microclimates that are cooler or warmer than the surrounding area. These microclimates may have lower temperatures because they are slightly elevated or subject to cooling breezes. Finding and using microclimates may lead to success with peonies.
Use caution when growing peonies around children or pets, as all plant parts can cause stomach distress if ingested.
- USDA Plant Hardiness Zone Map
- Los Angeles Times: Beyond the Zone
- The American Horticultural Society Encyclopedia of Plants and Flowers; Christopher Brickell, Editor-in-Chief
- Missouri Botanical Garden: Plant Finder -- Paeonia "Pink Double Dandy" KEIKO
- North Carolina State University: Horticultural Information Leaflets -- Peonies for the Home Landscape
- Photo Credit Comstock/Comstock/Getty Images