Every summer there are days when the heat is sinister — hot outside, hot inside. The A/C is on but my ’20s Spanish home is still 84 degrees. I pad back and forth, feeling like a snow leopard in an Arizona zoo. I eye my garden and pine for shade.
Trees. I need more trees.
“Trees are the most beneficial plants in our urban landscape,” says landscape architect and Cal Poly Pomona professor emeritus Bob Perry, conveniently supporting my obsession. Trees not only shade our homes, he points out, they also sequester carbon from the atmosphere “and transpire their moisture, which [reduces] air temperature and direct-sun heat load on our houses.”
With temperatures rising and Southern California vulnerable to drought (despite recent rain), cultivating shade just makes sense. Sure, gardening in the shade can be tricky, but with a little know-how, you can cultivate spots that are cool, lovely and soothing.
Over the 13 years I’ve lived in San Gabriel, I’ve added shade to my lot: a native Catalina cherry, some gorgeous red-barked manzanitas, a feijoa (pineapple guava tree). But as the trees have grown, the shadows have deepened and I’ve had to reexamine what will thrive.
To state the obvious: Plants need sun to photosynthesize and grow. That makes deeply shady areas, including the north side of structures, a challenge for gardeners. For these full-shade spots, Perry recommends understory plants from temperate or subtropical climates—flora that evolved to grow beneath a thick tree canopy. That includes the Japanese aucuba (Aucuba japonica), an evergreen shrub with variegated leaves; various maples, aspidistras and philodendrons (both commonly sold as indoor plants) and some species of Berberis, such as Oregon grape (Berberis aquifolium) and creeping barberry (Berberis repens).
Many of these plants need year-round water to look their best, so I prefer plants from Mediterranean climates — California, Chile, South Africa, Australia and the Mediterranean basin. Perry recommends these as well. “It’s a limited palette, but dry shade is as tough as it gets,” he says. “When you talk about dry shade, you are dealing with sort of a double negative.”
Las Pilitas, a native plant nursery near San Luis Obispo, offers an exhaustive list of California flora for full and dry shade on its website (laspilitas.com), with the caveat that many might prefer partial shade. Among the more popular plants on the list are various species and cultivars of coffeeberry, monkey flower, Heuchera, currants (Ribes indecorum and Ribes sanguineum glutinosum) and hummingbird sage.
All of these natives have thrived in shady spots in my garden. On the north side of my home, along a path between the house and a perimeter wall, I converted a dank zone of calla lilies and lawn into a thicket of (mainly) natives. The new plants mostly thrived and didn’t need as much water, but I discovered that each niche had its own microclimate. Several patches turned out to be sunnier than I thought, affording me a wider range of plants.
Jill Morganelli, horticultural supervisor for the Los Angeles County Arboretum and Botanic Garden, recommends studying your shade before you plant. “Maybe keep a little journal,” she says. “Go in the morning and see what the sun is, go out there in the afternoon, and then you also have to do that at different times of the year.”
My thicket matured, providing an attractive privacy screen, but some of the plants, including a nectarine tree, languished as others grew up around them. At the northwest corner of the house, a manzanita caught late-afternoon sun in summer. It grew slowly but steadily, eventually shading out a coffeeberry shrub.
“Most trees need full sun,” says Morganelli, “and when you start getting into shade and growing against buildings, there’s no air flow, so molds and root rot can really intensify.” She adds that people tend to overwater shady areas, leaving plants vulnerable to disease.
I’m stingy with water, so my biggest problem is determining whether aggrieved plants have taken too much umbrage or are in need of a drink.
Morganelli strolls among ferns at the Arboretum in Arcadia. She points out other shade-tolerant plants: orange-flowered Clivia, an evergreen, bulb-like (rhizomatous) plant from southern Africa; Peruvian lily (Alstromeria); and shrimp plant (Justicia brandegeana), a shrub with blooms resembling crustaceans.
Because shady areas are darker, Morganelli says, variegated and white-flowered plants, including the lighter azaleas, look especially pretty. “At night it literally illuminates your garden,” she says.
On hot days, one of Morganelli’s favorite Arboretum roosts is a bench under a stout coast live oak. ”Don’t try to plant magnificent gardens under oaks,” she advises. “It’s just not going to work.” Indeed, because of the deep shade and chemicals (tannins) this tree exudes to inhibit other plants, nothing is growing under it. “But look at the glorious shade,” Morganelli says.
The Arboretum’s Engelmann oak grove is a refuge for L.A. County’s largest remaining congregation of these rare native trees. I asked Jim Henrich, the Arboretum’s curator of living collections, to meet me there to discuss gardening around oaks.
The Engelmanns slant west in unison, a carpet of weeds at their feet. Henrich hopes to replace the weeds with a few sparsely planted natives, perhaps evergreen currant and bunch grass — but around the periphery. “The best thing of all is not to plant under the tree,” he says, “and just allow natural leaf-litter accumulation. It’s the best mulch.” California oaks are adapted to dry summers. New plantings will need more frequent summer water, which can leave oaks vulnerable to fungus, especially if moisture concentrates near the trunk. (One exception: In the first few years, young oaks benefit from regular water.) For trees generally, it’s best to water at the dripline — the zone under the outer circumference of the branches.
“If you have to plant under the tree, you should probably stay at least 15 feet away from the trunk,” Henrich says, adding that you’ll need to select plants that survive on less frequent but longer (deeper) watering. To avoid excessive root disturbance, keep plantings sparse. It’s good advice for working around any kind of tree.
Perry recommends installing a drip irrigation system at a tree’s dripline. “Cover it with mulch and strategically plant,” he says. “Put an emphasis on plants that spread and sprawl.” Cluster things, he says, so instead of a carpet, you’ll have mulch and “drifts and groupings and islands” of plants.
First and foremost, water the trees. “Our big trees, even coast live oaks, are not necessarily water-thrifty plants,” says Perry. “They have a big surface area to cool.” So prioritize: allow portions of your yard to be drier, rely less on lawn and other thirsty plants. That way, says Perry, “collectively you’re using less water because you are focusing it strategically on the plants that really do the good things for our environment.”
Exactly. Trees. Big shady trees.