Garden Update: The San Diego Botanic Garden

By: David Ehrlinger

David Ehrlinger has a background in botany from the University of Michigan. After several years as head of horticulture for…

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A variety of perennials, woody plants, cycads, and bulbs were planted in the understory of existing trees in the African Garden. Photographs are by Herb Knufken, except as noted

A variety of perennials, woody plants, cycads, and bulbs were planted in the understory of existing trees in the African Garden. Photographs are by Herb Knufken, except as noted

Two years ago, Quail Botanical Gardens changed its name to San Diego Botanic Garden to better express its identity in the San Diego metropolitan area. Less than a mile from the Pacific Ocean, it enjoys a virtually frost-free climate, allowing the staff to grow a wide array of plants—from palms and cycads to bromeliads and aloes. The botanical collections are displayed in twenty-seven gardens; several of the older gardens have recently been renovated.

Lying at the heart of the San Diego Botanic Garden (SDBG) is the African Garden, situated between the Visitor Center and the 1918 Larabee House. It includes the oldest tree in the garden, a skyline gum (Eucalyptus cladocalyx) over eighty feet tall. In 1943, Ruth and Charles Larabee purchased the property and set out a number of plants on the grounds, many of which survive today.

In 1957, Ruth Larabee donated the property to the County of San Diego to be developed as a park. It opened to the public in 1971 as Quail Botanical Gardens, with many new plants throughout the grounds, added by the late curator Gil Voss. Voss established geographically organized gardens, among them the African Garden. In the early 1980s, trees and shrubs were added to the African Garden by horticulturist Steve Brigham (author of Ornamental Trees For Mediterranean Climates, The Trees of San Diego). Brigham donated some of the trees; other donations came from Bill Nelson, of Pacific Tree Farms, and the Huntington Botanical Gardens.

African tulip tree (Spathodea campanulata)

African tulip tree (Spathodea campanulata)

Notable specimens from the Garden’s County era include African tulip tree (Spathodea campanulata), African trumpet tree (Markhammia lutea), strawberry snowball tree (Dombeya cacuminum), pink dombeya (D. burgessiae), forest gardenia (Gardenia thunbergia), teddy bear palm (Dypsis leptocheilos), and a number of large African cycads (Encephalartos).

In 1993, the private, nonprofit Quail Botanical Garden Foundation assumed management of the Gardens. Since then, the African Garden has gained more plants and expanded in size. In recent years, however, the garden has needed major rehabilitation and some aesthetic enhancement. Pruning was overdue; weeds, including volunteer trees and shrubs, were prevalent in the middle of the garden, and suckering shrubs like African linden (Sparmannia africana) needed to be restrained.

In 2010, we renovated the African Garden in honor of Bill Teague, our late horticulture specialist and a prominent local plantsman and garden designer. Bill provided aesthetic direction and helpful encouragement through most of the renovation. He passed away later in the year.

Bill favored the use of large boulders to add interest and a sense of permanence to a garden. A rugged sandstone outcrop bisects the African Garden’s hillside site. To accentuate the elevation change and add greater depth, we added boulders along the walkways: quartzite boulders along the upper western edge of the garden adjacent to the Herb Garden, large granite boulders along the eastern lower section. Natural quartzite and granite rock formations can be found within a few miles of the Garden.

The African Garden begins north of the Gift Shop and runs along a walkway under an intermittent canopy of trees. To carpet the ground, we planted colorful herbaceous perennials, including Clivia, Osteospermum, Sutera, Lobelia, and gerbera daisies (Gerbera). In the sunnier spots, cultivars of fortnight lily (Dietes), Agapanthus, fairy wand (Dierama pendulum), and red hot poker (Kniphofia) now provide flowers and contrasting foliage. Cape heather (Erica canaliculata) and breath-of-heaven (Coleonema album, C. pulchellum ‘Compacta’, and C. pulchellum ‘Sunset Gold’) add fine-textured foliage and spring flowers. The bold foliage of mountain cabbage tree (Cussonia paniculata) and several restios or Cape rushes provide further foliage contrast.

On the upper side of the garden is a sunnier, drier site. Here, we placed large African cycads (Encephalartos longifolia, E. transvenosus, and E. horridus), along with shrubs, perennials, and succulents, such as African daisies (from Arctotis to Osteospermum), Protea, Leucospermum, and Leucadendron. Several Aloe species have been planted along with their smaller relatives, Gasteria and Bulbine. Gasterias prefer shadier sites, while bulbines like the sun and flower much of the year. Other succulents in the garden are Crassula, Cotyledon, Aeonium, and Kalanchoe. We also tucked in a number of African bulbs, such as species of Gladiolus, Crinum, Watsonia, and Babiana.

New colorful interpretive panels now describe the garden and its several themes: the flora of Africa and Madagascar, cultivated landscape plants, African daisies, and African cycads.

The Lawn House Garden: new drought tolerant plantings with a tropical look in the foreground against the long-established background plantings of the high water use Tropical Rain Forest

The Lawn House Garden: new drought tolerant plantings with a tropical look in the foreground against the long-established background plantings of the high water use Tropical Rain Forest

The Lawn House

Another recent renovation was completed at the Lawn House, built as a barn, then converted to a guesthouse in the late 1940s, and now used as a multi-purpose facility for classes, meetings, offices, and storage. The “backyard,” always sparsely planted, had never been open to the public. We decided to install pavers and retaining walls to create a new and appealing space to hold weddings and special events.

The backdrop of the Lawn House is our Tropical Rain Forest display, featuring an exotic South Seas landscape of luxuriant palms, bamboo, angel’s trumpets (Brugmansia), tipu trees (Tipuana tipu), streams, and waterfalls. We wanted to bring this exotic atmosphere into the new backyard landscape, but with low-water plants that have a tropical look. This would serve the interests of both water conservation and plant health, by minimizing irrigation to reduce the risk of adversely affecting two forty- or fifty-year-old cork oaks (Quercus suber) on the garden’s west side. This new low-water landscape thus uses our Tropical Rain Forest for shakkei, or “borrowed scenery,” as employed in Japanese gardens.

Instead of planting bananas, with their big, bold leaves, we substituted the more drought-tolerant giant bird-of-paradise (Strelitzia nicolai). Other plants were chosen for their large, glossy, exotic leaves or long flowering season. Among the Mediterranean natives we used were a glossy-leafed hybrid rockrose (Cistus ‘Elma’), Gladwin iris (Iris foetidissima), Arbutus ‘Marina’, and oleander (Nerium oleander ‘White Sands’). We blended in some California native plants, such as island alum root (Heuchera maxima), giant chain fern (Woodwardia fimbriata), and lilac verbena (Verbena lilacina). We added a few foxtail agaves (Agave attenuata) for additional foliage contrast. For floral effects, we used low-water-demanding flowering perennials like Gaura, Euphorbia DIAMOND FROST, and Japanese anemone (Anemone xhybrida ‘Honore Joubert’) for its late season flowers and distinctive foliage.

A low-water, tropical species that grows well in our coastal climate is the common houseplant, Dracaena marginata. It is probably not as drought tolerant as its relative, dragon tree (D. draco), but it certainly has proven tough in this garden. We also used Sanseviera masoniana, which has much larger, broader leaves than the common snake plant or mother-in-law’s tongue (S. trifasciata), but has similar low water needs. Another houseplant used is cast iron plant (Aspidistra elatior); quite cold hardy, this exotic-looking perennial can be grown along much of the West Coast in protected sites.

To fill the garden with fragrance for evening events, we incorporated sweet olive (Osmanthus fragrans), the new seedless SNOW PRINCESS sweet alyssum (Lobularia maritima ‘Inlbusnope’), and FIRST LOVE gardenia (Gardenia jasminoides ‘Aimee’ grafted onto the more drought-tolerant G. thunbergia rootstock).

Dragon trees (Dracaena draco) and various Echium species are features of the Canary Islands Garden

Dragon trees (Dracaena draco) and various Echium species are features of the Canary Islands Garden

Canary Islands Garden

The third garden renovation began when a local church group offered to do a service gardening project. I suggested cleaning up the neglected back area of our Canary Islands Garden. The group energetically pulled weeds, raked, pruned back overgrown shrubs, and dug up or pulled out dead and dying shrubs. By the end of the day, they had really jumpstarted a clearly much-needed renovation project.

Opened in 1995, the Canary Islands Garden features mediterranean-climate plants from the cluster of islands off the northwest coast of Africa. Huntington Botanical Gardens provided a number of species, and the late Jack Catlin, noted aeonium hybridizer, donated an assortment of Aeonium species. Many of those original plants have since died, but others or their progeny have persisted. The highlight of the Canary Islands Garden is a grove of dragon trees (Dracaena draco), the oldest specimens planted in the late 1940s and 1950s. Torrey pines (Pinus torreyana) were also planted then, so much of the garden is now in full or partial shade. Only a few plants were added during the County era from 1957-1993.

White tower-of-jewels (Echium simplex) in blossom with dragon trees in the background. Photograph by Sally Sandler

White tower-of-jewels (Echium simplex) in blossom with dragon trees in the background. Photograph by Sally Sandler

Tower-of-jewels (Echium simplex) grows well in shady sites, and its white floral spikes are elegant in spring. The shrubby, white-flowered E. decaisnei has done well, though preferring as much sun as possible. The common but showy pride-of-Madeira (E. candicans), from the nearby Madeira Islands, grows prolifically in this garden, so much so that its many seedlings require removal. We planted Canary Island sage (Salvia canariensis), tree euphorbia (Euphorbia lambii), Canary Island euphorbia (E. canariensis), Persea indica, various Aeonium species and hybrids, and tree sonchus (Sonchus canariensis), a shrubby species quite unlike the weedy common sow weed (S. oleraceus).

The Garden’s horticulture staff continued the renovation work begun by the church group, progressing deeper and deeper into the mostly evergreen border between the Canary Islands Garden and the Central American Garden beyond. We cleaned up a tangle of overgrown shrubs and trees and discovered a den of nasty invasive and otherwise unwanted plants that often infest dark and neglected garden nooks and crannies. Fifteen-foot-tall Brazilian pepper trees (Schinus terebinthifolia) and a Victorian box (Pittosporum undulatum) masqueraded as desirable evergreen screening shrubs. Clambering over and through the echiums was a wild patch of Japanese honeysuckle (Lonicera japonica). A large swathe of English ivy (Hedera helix) was revealed. The worst weed, by far, was perennial veldt grass (Ehrharta erecta), insidious because of its tolerance of shade and drought, its rapid growth, and its prolific seed production. We also found a few seedling Mexican fan palms (Washingtonia robusta), Canary Island date palms (Phoenix canariensis), carrotwood (Cupan-iopsis anacardiodes), and even a couple of young giant bird-of-paradise.

Most of this renovation has involved editing out weedy, undesirable plants and overgrown and declining plants. We replaced the evergreen screen with an avocado relative (Persea indica), dragon trees, and shrubby species of Dendriopoterium and Echium. Along some of the more heavily trafficked pathways, we planted Marguerite daisies (Argyranthemum frutescens), Perez’s sea lavender (Limonium perezii), and lots of aeoniums, mostly Jack Catlin’s hybrids (‘Cyclops’, ‘Velour’, and ‘Blushing Beauty’). Because of its rampant nature, Algerian ivy (Hedera canariensis), native to the Canary Islands as well as northwest Africa, has been confined to container plantings.

It’s best to think of these garden improvements (perhaps garden renovations in general) as never being complete. There is always something more to do: fall planting, sticking in more aeonium cuttings, thinning out Torrey pines, and weeding. Garden making is never really done, but the progress we have made in recent years is adding even more excitement to the San Diego Botanic Garden. Drop by and see what we have accomplished.