Despite the Coachella Valley’s near tropical climate, creating gardens in this desert can be trying. Wind, heat, sand and a dozen other factors must be considered and then solved or mitigated before plants will grow. With its topsy-turvy planting and growing seasons, just about anything will grow in the valley’s year-round sunshine, given enough time, abundant water, and well-drained soils.
Maureen Gilmer’s book; Palm Springs-Style Gardening, reveals that it isn’t all cactus and palms, but a wide variety of desert plants that shower the landscape in candy-bright blossoms, interesting textures and sculptural forms. Based on her many years as a landscape architect, avid horticulturalist and local resident, Maureen offers invaluable tips and handy instructions to help keep your desert garden looking its best. The following excerpts are generously shared from her book.
The Coachella Valley enjoys over three hundred days of sunshine per year. The dry air is so lacking in moisture there is little atmosphere to diffuse ultraviolet light, allowing the sun’s full intensity to strike the ground. It is why Palm Springs became synonymous with both the winter tan and skin cancer. Cacti indigenous to this region have evolved to thrive in intense ultraviolet light, but even these struggle in the summer months here. Many permanent plants that demand full sun in normal atmosphere can suffer significant problems in direct low desert sun. The change of seasons alters the position of the sun in the sky. As it moves further south for the summer and then north again in the winter, the exposure of plants is varied. Container gardens make sense because they can be moved with the seasons to protect against midsummer sun damage and winter frost.
Plants react to excessive sun in different ways. Leaf scorch results in brown blotches or the crisping of leaf edges. With succulents, the plant becomes yellow under too much direct sun. This color may fade back to green as the seasons change. But when the exposure is just too great and permanent damage results, the yellow continues to discolor to brown, with ugly scabbing. For a beautiful green skin cactus or succulent euphorbia with few thorns, this can result in irreparable damage.
The wind farm at the west end of the Coachella Valley attests to the epic winds experienced here. The old tamarisk tree windbreaks were planted to reduce its effects and that of blowing sand so severe, it can pit automobile glass. It is difficult for even desert-adapted plants to survive these conditions. In some seasons, typically spring and fall, high winds cause broken branches and blow-over of trees. Just take a look at the trees in Desert Hot Springs to see how wind can spoil their form and thin foliage. Even tough palms and moisture holding succulents have a hard time there, and those that manage to survive lose their natural beauty. The biggest challenge of wind is desiccation. This is the drawing of moisture out of the leaves of a plant through tiny pores known as stomates. Plants that evolved in and regions around the world have natural defenses against wind borne moisture loss. Try to grow plants from more humid climates and they’ll instantly wither.
When the rate of moisture loss becomes greater than the rate at which the roots can replace it, leaves die. Few new ones form. This makes it nearly impossible to get a young tree started because it is water-starved from day one. Older trees may leaf out in calm periods only to be stripped again by wind.
In ancient times the Coachella Valley was once an inland sea. It was named after the Spanish word for shell, and you can still find small seashells in some soils here. The soil is noticeably lacking in organic matter, so its fertility tends to be limited in the west end of the valley. In more recent history just a few centuries ago, a great lake lay at the east end of the valley and was ringed by extensive marshland that drew Native Americans from all directions to hunt water fowl and to fish. This is why soils around Indio are so fertile they support extensive agriculture. Soils in the Palm Springs and Desert Hot Springs are influenced by the windy pass and tend to be heavy with sand. The same is true down the wind belt of Thousand Palms and Bermuda Dunes. Drainage is expressed and there is little nutrition for plants not adapted to a Spartan diet. However, these can be some of the best soils for gardening because we can augment them with bagged compost and fertilizers, both organic and synthetic. Sandy soils will dry out very quickly, so it is essential to water often to keep plants adequately hydrated in the summer months. This is doubly important in the wind belt communities.
Around the foothills that edge the valley which include the coves of La Quinta, Palm Desert, Cathedral City, and south Palm Springs including the Mesa, soils can be more challenging. They are rocky and the earth can reach the consistency of concrete with only slightly greater fertility than the sand. Some of these hardpans exposed to water experience natural cementation due to minerals which set up much like concrete. This cementation can restrict drainage so that water applied runs off before it is absorbed slowly into the soil. Therefore irrigation must be carefully designed to mitigate this poor drainage and maximize its effectiveness with much slower applications. For these soils, the best way to improve conditions is the healthy addition of finely ground compost. Organic matter interferes with the natural cementation, keeping soil particles from packing so tightly together.
Water is the desert’s most precious resource, and sadly it is too often exploited in our valley. Lawns and golf courses are the major offenders that require incredible amounts of irrigation to survive here. The best way to water in the desert is to supply water to a plant and nowhere else. Not only does this reduce weed growth and maintenance in the desert landscape, it makes your plants far more healthy. Their water demands in the hot months are greater than traditional spray systems can provide. But there is another reason why spray systems can be a problem. Plants root only where there is water. When a spray system covers large areas with airborne spray, the water you apply must reach a huge area of ground. The moisture penetrates only a few inches deep, which is adequate until the next watering time in the cycle. The plants will concentrate their roots in that shallow layer to capture as much moisture as they can. But come summer and the surface temperature of the soil skyrockets. This water grows less abundant and the roots are subjected to the full force of surface soil heat. Without the ability to root for deeper hidden moisture, they fail to do well and may die if there is a sudden
Spray systems can also have big problems in windy climates. New homes in the wind belt will suffer the most from water drifting out of its designated location in gusty weather. Stream heads were designed to water better under these conditions, but even these can be challenged by desert conditions. The key to success is to think about flooding the root zone with water. This was traditionally done with a bubbler head on a standard riser that supported one tree or shrub. They emit a great deal of water and one or two can support a sizeable tree. The water pools around the base of the tree to gradually percolate down to a greater depth than spray. When the surface soil heats up and dries out, there will be plenty of water deeper down, so roots naturally seek it out.
Even if you leave the valley for the summers, your garden doesn’t. Every plant that is to remain behind must be tolerant of the summer here. Next to Death Valley, the Coachella Valley summer is the hottest in the United States. Do not confuse heat with solar exposure. Heat occurs whether a plant is in full shade or sun, under cover, or out in the open. It is the ambient air temperature that can reach staggering levels in July through September. Many plants that are suited to warm climates may not be able to tolerate these temperatures even under the best conditions. This is why you never see certain plants in valley landscapes that hail from warm climates elsewhere. For example, New Zealand Flax, a very popular plant for droughty gardens and landscaping along Los Angeles freeways, thrive west of Banning. But try to grow them in the valley and they literally melt down. Meltdown is a common term to describe how a plant collapses from the heat. The cells that make up its structure literally disintegrate and the plant is lost. No amount of care, relocation, or water will save it. This reaction is purely genetic and indicates the plant simply won’t grow in our climate.
Sometimes nursery plants grown in coastal nurseries and brought into the valley to be sold will exhibit the very same characteristics. This meltdown may not be genetic, but a reaction to suddenly being forced into such a blistering climate. Their stomates are much larger to allow for greater transpiration rates on the mild coast. When they come here, too much moisture is lost through the stomates and the plant withers. Sometimes it will die back to the stem or root, but don’t be in a hurry to dig it out. This remnant may regrow next year. But this second grow-out will bear smaller leaves with more efficient stomata.
Maureen Gilmer has 35 years experience in horticulture and land- scape architecture. She is the garden columnist for The Desert Sun and writes a nationally syndicated column for Scripps News. Maureen is a photographer and author of many gardening books. She writes content for various horticultural companies and magazines, but still designs gardens for a select few. Follow her newspaper columns and join the fun on Pinterest and Facebook, where she’ll keep you up to date with signs and seasons of gardening in the Coachella Valley and High Desert.