The whole of California is officially in a drought. An arid landscape devoid of moisture, our yearly precipitation is quite meager in coastal California. The mild climate, largely devoid of bugs and humidity and the typical blue skies are largely what attract hordes to continue to flock to the Golden State. Furthermore, the rain that does come arrives sporadically in episodic deluges, generally occurring between November and April. This means eight to ten months of no rain, except for the night’s fog-drip. In such episodic hard rain storms, six months of rain may fall in a forty-eight hour period, sheeting down driveways, running down on-ramps and gliding downslope and away from our gardens. Such storms happen in a flash, and are acute times of topsoil erosion, as well as the time when the opportunity for rain harvest is manifest. Impervious surfaces, such as concrete, work to accelerate the speed of rain runoff and create no opportunity to harvest the bounty of this water.
California is growing by nearly half a million people per year. Many of these migrant Americans come from places east of the Rockies, lands full of year-round precipitation. As they begin to move into the California landscape, they often bring with them the expectation of a lush oasis. It is inherent in our human DNA to favor such oasis. However, until recently we have taken for granted the viability of limitless water. San Francisco, like San Luis Obispo and much of coastal central California receives 18 to 20 inches of rain per year. Los Angeles, further to the south receives a scant 15 inches per year.
The average California resident “uses 110 to 130 gallons of water per day, of which up to fifty per cent is used outside for the yard. “Of this half,” says water economist David Zetland, “up to eighty percent is used for the watering of thirsty lawns”. Clearly lawns, our biggest single drinker of residential water, are beginning to be noticed and identified as too thirsty for drought conditions.
According to the Los Angeles Metro Water District, the average Los Angeles lawn uses the equivalent of 84 inches of rain per year to water a lawn planted in a place that receives 1/4 of that rainfall (LA Metro Water District). With residential restrictions being enacted in municipalities throughout coastal California, it is time for a dialogue about how to create lush oases around our dwellings, while working with the forces of nature. We can start by considering what we plant. California Native plants, Mediterranean plants and succulents have evolved to naturally be in sync with eight-plus months without rain. One way they can do this is by absorbing the night’s fog-drop, which can actually be the equivalent of up to 10 inches of rain per year. Another way people are finding efficiency in their home landscape is to utilize greywater from the washer and sinks to reallocate in the garden. Some people are harvesting the rain that falls on their roofs by way of rain barrels, to store for later usage. This is a great method to lessen our demand on municipal water. However, this rain catchment is not the only way to hold on to and slowly release the rain. By channeling moisture through our hill slopes in a process called earthworks, we can set the stage and then let the rain work for us and our garden.
Earthworks: “SLOW IT, SPREAD IT, SINK IT:
As rain falls it streaks down stalks of plants and runs down slope toward the nearest drainage and eventually to the sea. Water always finds the path of least resistance, the most efficient route downhill. On steep slopes this run off can pick up speed and momentum, taking soil particles and, at time, causing catastrophic collapse, as the Southern California mudslides have repeatedly shown.
Steep topography throughout coastal California allows us to work with the slopes to harvest rain. Many slopes on our residential homes and ranches are left bare. Earthworks allow us to create swales that become temporary repositories, allowing the rain to linger on our hillsides long enough to infiltrate the topsoil at a rate that plants downslope can uptake, thus extending the wet period for our cultivated plants.
Slope stability and soil retention
Long droughts exacerbate the difficulty plants have getting started on steep slopes.
By mulching three to four inches deep on slopes downhill from swales, we can create habitat for mycorhyza, or beneficial mushrooms, to colonize. This moist mat holds the soil and allows small, new plants a better chance for survival. Mulch and mycorhiza are key components, along with moisture that begin to create a living soil. This creates a positive feedback system, as more water creates more root growth and more mycorhizal mat, which in turn increases the water-holding capacity of an area, thus increasing the ability for new plants to fill in the gaps, fostering a healthy network of what soil scientist Dr. Elaine Ingham has termed the “soil food-web.”
Net and pan systems allows steep slopes to become areas that channel moisture into production pockets. These pockets can then produce Mediterranean fruit trees, such as olives and pomegranates. In each basin, under said fruit trees, edible annual crops such as arugula and squash can offer a second and third crop, while also acting as a living mulch. Thus, earth works begin to steer the water through the landscape, creating wet zones and dry zones. The wet zones can be centers for food production. The dry zones can incorporate drought tolerant specialists such as Mediterranean and native plants such as California poppy, lavender and rosemary. By shaping our slopes, we can slow the rain water, build the soil and stabilize our hillsides while creating oases of food and ecology.
Action Steps: Assess your property.
- Where are your rain gutter downspouts?
- Is there an opportunity for rain barrels/water storage?
- How can washing machine effluent get incorporated into the garden?
Joshua Burman Thayer is an Ecological Landscape Designer and Educator who runs Native Sun Gardens, based in the Bay Area.