Plant in Shade and Let Trees Live : Fungus: Too much watering can cause root disease. The trick is to grow those varieties of plants that require a minimum of water.
A magnificent old shade tree is both an opportunity and a paradox. It fairly begs to be underplanted with azaleas, ferns and other shade-loving plants that, with generous summer watering, will create a verdant woodland scene typical of areas that receive many times our annual rainfall.
The paradox is that the heavy watering given such a planting can cause the death of the tree it was meant to accompany.
This sad scenario most often involves native oaks, which are prone to armillariella root-rot, but that disease, also called oak-root fungus, affects a wide variety of other woody plants.
In fact, the list of trees that don’t get oak-root fungus is a rather short one. Overwatering also aggravates verticillium wilt and other root diseases that can kill camphor, Victorian box and other shade trees, especially where drainage is poor. Mature and senescent trees are in more danger than younger, vigorously growing specimens.
To preserve an old tree and conserve water at the same time is a noble undertaking, but what about that lush shade garden? In the case of an existing garden, the question to ask might be: Do these plants really need all the water I’m giving them?
Camellias and azaleas are favorites in Southern California shade gardens, and it is axiomatic that they require heavy summer watering. But if gardeners would give their sprinklers some time off they might be in for a pleasant surprise. Mature camellias in shade need very little watering and can be seen surviving around long-vacant houses, blooming freely in spite of drought and neglect.
Camellias are slow to reach that stage of maturity, but even plants that only have been in the ground three to five years can go two or three weeks between waterings.
Azaleas are much less drought-tolerant, and their foliage can be rather badly damaged if allowed to wilt for as long as a day. Still, overwatering is a frequent cause of death for azaleas, as constantly saturated soil lacks air that azaleas need in their root zone for good health.
Other familiar plants grown in the shade that thrive on frequent watering but that actually require much less, once well-established, include clivia, star jasmine, nandina, aucuba and Philodendeon selloum. Almost all ferns have higher water needs, but chain fern, Australian tree fern, Japanese felt fern and hare’s foot fern are some that withstand dry periods.
If you have reduced the irrigation of your shade garden and find that certain plants always wilt or show other signs of drought-stress before others, consider concentrating the more moisture-loving species in a separate area. Otherwise, you may be overwatering 80% of your shade plants to satisfy the 20% that need more water.
If you are planning a water conservative shade garden, a visit to the nursery might reveal some new choices to combine with old favorites, or to make up a whole garden by themselves.
Nothing creates a more harmonious garden scene than a grove of native trees underplanted with shrubs and perennials that are their companions in the wild. At the Theodore Payne Foundation’s nursery (10459 Tuxford St., Sun Valley, (818) 768-1802) you will find California natives that form the natural under-story for our coast live oaks, Engelmann oaks and valley oaks.
Two of the best local natives for shade are fuchsia-flowered gooseberry ( Ribes speciosum ) and meadow-rue ( Thalictrum polycarpum ). The gooseberry is a thorny, 4-foot shrub with shiny, inch-wide leaves and pendent red flowers that are an important nectar source for hummingbirds in winter.
Meadow-rue is an evergreen perennial forming an 18-inch clump of graceful blue-green foliage reminiscent of columbine. Both become established quickly, and after their first year in the ground, should only need monthly soakings during hot, dry weather.
From the Sierra foothills, bush anemone ( Carpenteria californica ) is a rare evergreen shrub noted for its display of large white flowers in spring and summer. Good companions for bush anemone are the hybrids of Iris douglasiana and other native iris species in shades of purple, blue, yellow and white.
Though not especially attractive plants when out of bloom, these spring-flowering perennials are outstanding for their wide tolerance of soils, sun, shade and much or little watering.
Another handsome pair of natives for dry shade is creeping mahonia ( Mahonia repens ) and evergreen currant ( Ribes viburnifolium ). Mahonia is an erect plant to 3 feet tall that slowly spreads by roots to form colonies. It bears yellow flowers followed by blueberries, and in cool weather its blue-green leaves take on pretty tones of red and purple.
Evergreen currant, native to shady canyon slopes of Catalina Island, has reddish trailing stems clothed with pleasantly fragrant dark-green leaves.
These two shrubs require good care to become established and develop properly. Consistent watering during their first two sumemrs in the ground, pinching the currant to encourage branching, and cutting back the tallest, woodiest stems of the mahonia to encourage new shoots from the base result in full, attractive plants with good drought tolerance.
California natives are obviously moving up in the world as a number of them, including the mahonia and ribes are for sale at Burkard’s (690 N. Orange Grove Blvd., Pasadena; (818) 796-4355), a nursery where many a hard-to-find plant has been found at last.
Recently, a specimen of Garrrya elliptica ‘Evie,’ a spectacular cultivar of the coast silktassel bush that had been special-ordered from a Northern California grower, was awaiting its new owner.
The majority of native-plant wholesalers are located between Santa Barbara and San Francisco, and Frank Burkard Jr. says he is happy to order unusual natives from them at customers’ request but cautions that sometimes a wait of several weeks is involved.
Spotted among the shade plants at Burkard’s were several sought-after shrubs and perennials that prefer drier conditions, including Corsican hellebore, a robust, long-lived perennial that is rare in the nursery trade due to difficulties in germinating its seed.
Aucuba japonica , represented at Burkard’s by its familiar yellow-speckled form and also the cultivar ‘Serratifolia’ with very different narrow, saw-toothed leaves, is a shrub that tolerates deep shade.
Once established, it fares best with infrequent irrigation as overwatering causes a disfiguring leaf-spot disease. Variegated winter daphne ( Daphne odorata ‘Marginata’) is said to produce its intensely scented flowers more freely when kept rather dry in summer but “if you let it go bone-dry, it’s dead,” Burkard warns.
Burkard, a third-generation nurseryman recalls a challenging landscaping job in which the answer to the dark shade and troublesome surface roots of a group of Brazilian pepper was a ground cover medley of tough members of the lily family, including cast-iron plant ( Aspidistra elatior ), butcher’s broom ( Ruscus hypoglossum ), a variegated lily-turf called Liriope ‘Silvery Sunproof,’ mondo grass ( Ophiopogon japonicus ) and black mondo (O. ‘Nigrescens’).
In this composition, leaf color and texture provided interest in a dark, dry situation most plants would not tolerate.
The shade and deep litter under eucalyptus trees is not merely difficult for other plants, it’s actually poisonous. Chemicals leaching out of their fallen leaves into the soil act as herbicides to discourage other plants in the vicinity. In Australia’s eucalyptus forests, sword grass ( Lomandra ) is one of the few plants that seems impervious to this toxicity.
At Desert to Jungle Nursery (3211 W. Beverly Blvd., Montebello; (213) 722-3976) owner Gary Hammer is offering two species of sword grass collected on a recent trip to Australia. Lomandra longifolia forms 2- to 3-foot clumps of graceful, grass-like evergreen leaves that give the effect of a taller lily-turf. Its panicles of white flowers are now showy, but if it can co-exist with eucalyptus it promises to be a useful plant for many difficult dry shade situations.
Definitely more fetching in bloom is a ginger lily ( Alpinia caerulea ) with white flowers and blue fruits Hammer collected in an Australian monsoon forest with alternating seasons of torrential rain and severe drought.
Examining the thick, almost leathery leaves of shell ginger ( Alpiniazerumbet , A. speciosa ), Hammer remarks that of all the ginger lilies, alpinias are the best-equipped to withstand dry periods.
Climatic conditions similar to the monsoon forest prevail in much of tropical Africa and America, making these good hunting grounds for dry shade plants.
From Central America, Anthurium hookeri definitely has the rain forest look with its handsome 3-foot long leaves, but in the wild, Hammer has found it growing on arid sandstone slopes, enduring a dry season as long as ours although with higher humidity.
From the same area, the common parlor palm ( Chamaedorea elegans ) is feathery and delicate in appearance but can take “an amazing amount of drought” according to the well-traveled plants man. For planting in dry shade he also recommends bromeliads of the genus Aechmea from tropical America, sansevierias from Africa and Japanese felt ferns.
All nurserymen queried rejected the idea that any plant takes so well to dry shade that it simply could be planted and forgotten. As with water-conserving plants for sun, shade plants expected to ultimately withstand drought should be given careful, consistent watering for the first one or two dry seasons to enable them to develop strong root systems.
