Like most of the state, California’s Central Valley has a mediterranean climate, with hot, dry summers and cool, wet winters. Compared with coastal California, however, where most of the state’s horticultural resources are located, the Central Valley experiences greater extremes of heat, cold, and drought. For example, the record low temperature at Davis is 12° F, record high is 116° F, and average annual rainfall is only seventeen inches. Many areas of the valley also have heavy, clay soils, and the ground water used for irrigation in much of the valley contains high levels of bicarbonates. These bicarbonates, when applied to neutral or acid soils, raise soil pH over time, making the soil more alkaline, which restricts or eliminates the ability to grow many kinds of plants, especially acid-lovers like azaleas.
The Central Valley is the fastest-growing region of California; its population is expected to double within the next fifteen years. Many new valley residents are moving from California’s coastal regions. They may enjoy less crowding, lighter traffic, and a lower cost of living in the valley, but they will be frustrated if they try to replicate their coastal gardens in our inland environment. Many showy, tender plants common in coastal gardens grow poorly in the valley, and will require more water and soil amendments to survive. Plants under greater stress may also require more pesticides and more frequent maintenance to maintain a good appearance.
The University of California, Davis Arboretum has a strong institutional commitment to educating Central Valley audiences about regionally appropriate gardening. Arboretum staff have been selecting, growing, and testing plants under Central Valley conditions for seventy years. Recently, as part of a comprehensive horticulture education program supported by the Elvenia J Slosson Fund for Environmental Horticulture, our horticultural staff has identified fifty tough, reliable plants that have been tested in the Arboretum, are easy to grow, do not need a lot of water, have few pest or disease problems, and bring outstanding qualities to the garden. Many of them are California native plants, and many support native birds, butterflies, and beneficial insects. We call them Arboretum All-Stars, and we have introduced several new ways for gardeners to learn about these great plants.
Spreading the Word
Visitors to the Arboretum demonstration gardens will see a series of beautiful, brightly colored signs identifying the Arboretum All-Stars, each with a photo of the plant in bloom, a list of its outstanding features, and information about how to grow it. In some locations, plant labels also show the All-Star logo.
A searchable database of the All-Star plants is available on the Arboretum’s website (arboretum.ucdavis.edu), with color images, a description of each plant, and information on its requirements. The easy-search feature allows users to look for plants that meet the criteria they specify (for example, plants that grow in shade, have white flowers in June, or attract hummingbirds).
You can download and print out a list of all fifty All-Stars, with photos and descriptions, at the Arboretum website, as well as articles on recommended All-Star plants for water-saving gardens, wildlife gardening, and some of the best California native plants for inland gardens. These publications are also available at the Arboretum Headquarters and the Arboretum Terrace home demonstration garden in downtown Davis.
Many of the All-Star plants are available at Arboretum plant sales, where they are marked with the All-Star logo on special information cards. At the Arboretum nursery, volunteers have created an attractive display garden featuring many All-Star plants; here, shoppers can see the mature plants in a landscaped setting. Our sales assistants can direct shoppers to the All-Stars and help them choose the best plants for their specific garden conditions.
More Arboretum All-Stars to Come
The Arboretum recently received grants from the UC Davis Campus Sustainability Program and the federal Institute for Museum and Library Services to expand the All-Stars program and introduce new ways to learn about sustainable horticulture for the Central Valley. We will be adding fifty more plants to our All- Star list, focusing on those plants that we know are tough, adaptable, water conserving, and attractive. We plan to continue recommending California natives and other species that we know provide food for native birds, beneficial insects, butterflies, and other pollinators. We will be expanding the website to include these new plants, creating new demonstration plantings and educational signs for the gardens, and developing audio and video podcasts and cell-phone tours with a focus on sustainable horticulture.
Arboretum All-Stars for Spring
Chilean lily-of-the-valley tree (Crinodendron patagua) is a small, evergreen tree reaching fifteen to twenty-five feet tall, with small, shiny leaves somewhat like a live oak. In spring, it produces masses of delicate, white one-inch-long, bell-shaped flowers. Reliably heat and drought tolerant, it has been grown in the Arboretum with irrigation every two weeks, but also tolerates twice-weekly irrigation. Its attractive, evergreen foliage, upright form, and narrow profile make this plant a good screen or patio tree. (Sunset zones 14-24)
Great for shade or partial sun, Rosada coral bells (Heuchera ‘Rosada’) is a tough and beautiful perennial. A hybrid of two species, the Southwestern Heuchera sanguinea and H. maxima, from Southern California, it makes an attractive mound of foliage and is especially useful in dry shade such as that found under native oaks. Over a long bloom period in spring, it produces a showy display of creamy pink flower clusters on twenty-four- to thirty-six-inch stems. Drought tolerant and tough, this UC Davis introduction can adapt to a variety of conditions. (Sunset zones 14-24)
Another tough, drought-tolerant, native perennial is hummingbird sage (Salvia spathacea). Its sturdy stems, rising to three feet, have “shish kebab” whorls of red flowers nestled in green bracts. Highly attractive to hummingbirds, its flowers are produced in both spring and fall. The apple green, thick, triangular leaves offer a pleasant fruity fragrance that some find reminiscent of pineapple. This is an excellent groundcover for dry shade; we have found that it also tolerates full sun, where it produces even more blooms if given a little extra summer water. It can be found growing wild in the canyons of the Blue Ridge Mountains north of Vacaville in the Central Valley. (Sunset zones 7-9, 14-24)
Anyone who moves from the cold-winter climates of the Eastern states bemoans the difficulty of growing and blooming lilacs in the Central Valley-but they need suffer no more. Cut-leaf lilac (Syringa x laciniata) is one of the few lilacs that thrives in the Central Valley. This hybrid deciduous shrub sports attractive divided leaves instead of the solid eggshaped leaves of more common lilac selections. This lacy foliage is less susceptible to shredding and damage from hot summer winds, and gives the plant an airy and delicate appearance. This is a dependable and prolific bloomer with lavender pink flowers in open sprays that cover the plant in spring. (Sunset zones 3-12, 1-16, 18-22)
If You Should Like to Visit . . .
The UC Davis Arboretum is located on the Davis campus, stretching along the length of Putah Creek, with headquarters at LaRue Road. Plant sales are scheduled for April 7, April 21, and May 19, 2007, from 9 am to 1 pm at the Arboretum Nursery at Orchard Park. For more information about the UC Davis Arboretum, the All-Stars program, membership, volunteer opportunities, or directions and a map, please call 530/752-4880 or visit arboretum.ucdavis.edu.