After the Lawn: Assessing Your Garden's Water Needs

"The hills and lowlands are carpeted with living green, the air is redolent with mingled odors of roses and orange blossoms, and sweet songs of birds are heard everywhere. Nature is decked in the garb of summer the year round. The days are ideal and the nights are no less beautiful ... Almost anything will grow here, fruits, flowers and agricultural products alike..."
-- "San Gabriel Valley: A Vale That Lies Swooning in Beauty," Los Angeles Times, January 1, 1891

Ah, realtors. The idea that (almost) anything grows in Southern California was never true. That California's original sales pitch took more than a century to dispel is credit to how well aqueduct builders filled our garden hoses. But, as water becomes less available and more expensive, and the Imaginary Homeowners of this series have removed their lawn, they have a question. What actually does grow here?

The short answer: Less. The long answer has many variables. Yes, yes, yes, say the Imaginary Homeowners, but what about their jacarandas? Those beautiful trees front and back were the reason that they wrote a begging letter to the previous owners to sell the house to them. They're why they mortgaged themselves up to their eyeballs. Can they at least support their jacarandas with the proceeds of their rain garden?

In a staggering oversight, city watering ordinances have focused on lawn and forgotten trees. So the Imaginary Homeowners turn to a copy of Landscape Plants for California Gardens by former Cal Poly Pomona Professor Bob Perry. Scanning the irrigation tables, they realize that the answer is: Barring a disastrously low local rain year, probably yes. They can support their trees. They would be far better off it their street had been planted with native oaks that have low water needs in summer, but, in a year with only nine inches of rain, it would take infiltrating all the rain harvested from various roofs to keep the trees healthy. To keep tropical trees healthy in a Mediterranean climate, they would also need summer water. That would mean diverting half or more of the dry season tub and shower water to the jacarandas too.

The bad news? Even with greywater, the most they could add to the landscape without supplemental irrigation might be a spangling of California grey rush to help stabilize the soil of the rain garden arroyo. Beyond that, in dry years and summers, they're irrigating from the mains. They found room just outside the canopy line for a low-growing native coffeeberry 'Ed Holm' cultivar. It would need some supplemental water. Not much, but some. They're going for it. The four stone fruit trees would get run-off from the driveway and laundry water, but would also need supplemental irrigation. A dwarf Meyer lemon by the driveway could share greywater from the bathtub, but it would need occasional deep soaking from the mains, too. They hope their downslope neighbor will agree to a low water, dreamily aromatic Cleveland sage to billow over the property line by the driveway. Once established, that beauty will do a lot for very little. But that's it. And even keeping it so very simple, they missed their target of zero impact.

At this point, the Imaginary Homeowners have trouble fighting back a sense of gross betrayal. This wasn't what they signed up for. To grasp the enormity of the "anything grows" lie, they turned to a Perry study looking at a three-acre community park with an identical climate zone to the City of Los Angeles. There Perry found that in a "normal" 15-inch year, the rain that fell on the park barely met a tenth of the site's water needs. Lawn, which covered a third of the study area, took roughly half of the combined irrigation and rainfall. A food garden covering another third of the land used about a third of the total water. Finally, the Mediterranean and California native planting that covered the remaining third of the park took more than a sixth of the total water. Only a quarter of the native plant water needs were met by rain. Urban settings reduce their efficiency. By comparison, tall fescue turf grass needed fourteen times the amount of water supplied by rain.

The Imaginary Homeowners start grasping at straws. Ah, but the Perry test site doesn't have tanks capturing roof water! They'd heard advocates of tanks argue that water shortfalls could be made up by trapping rain in 10,000-gallon storage tanks front and back, then meting it out on an IV-basis.

And then comes the deflation. A tank might work down the line, particularly in back. However, beyond the staggering cost (underground tanks can cost roughly $1/per gallon of storage, above-ground ones are still in the thousands), placement challenges and questionable aesthetics, what would the impact be if they hoarded roof water? The thing that would miss it, they realized, was probably the single most important, most deserving element of the garden.

That would be the soil. The imaginary homeowners learned the difference between soil and dirt after sheet mulching over their lawn, then waiting a period of months to remove recurring weeds. To their astonishment, the ground had gone from compacted to sponge-like. Beneficial fungi and bacteria necessary for plant roots to thrive moved in. When it rained, the water soaked in rather than running off. Briefly, so briefly during rain, the falling water volatilized deep earthen aromas. Their idea of a vale of beauty became a well-mulched yard. The Imaginary Homeowners decided that drip is best for summer annuals such as tomatoes but, when it came to the wider landscape, drip alone wasn't sufficient. Their garden needed seasonal deep soaking.

As they looked at their paltry new plant list, they realized less was more if you counted soil. Protecting soil went far beyond treating it to big glugs of seasonal rain. It also meant eliminating competition on the surface. They would no longer have trimmers savage the jacaranda's canopy just so they could get light to the ground, which they'd jam-packed with groundcover plants around the tree's root zone. They were, they realized, asking too much of too little ground. As Fullerton-based arborist Kevin Holman said to them when asked about the single worst problem facing trees in Southern California, "Too many plants."

As they removed lawn, harvested greywater, worked with their neighbors on sightlines and drainage, the Imaginary Homeowners are all too aware that the "anything grows" era is forever over in Southern California. Block club meetings now routinely involve plant-editing sessions. Their first question: "What does that plant do for us?" If it doesn't satisfy at least one of a checklist that includes: save a family $200 a month on air conditioning, muffle noise, clean air, capture stormwater, feed someone, sustain birds that control pests, or go beyond merely floral fill to something of utter soul-replenishing beauty, they decide in fall pruning season to dispatch it to compost. "It isn't your grandmother," they joke.

The Imaginary Homeowners are on a roll. They may have fewer plants in their landscape, but they have healthier ones. Their soil is alive. With luck, no one on their block will need to call back Kevin Holman because their jacarandas are stressed or dying. Now all the Imaginary Homeowners have to do is become us, and not Imaginary.

Next week: The penultimate installment of After the Lawn looks at how and why to plant woody landscape plants only in the autumn to establish them during rainy season.

Follow the entire After the Lawn series:
After the Lawn: Part I
Designing Your New Garden
Caring For Your Turf
How to Remove Your Lawn
Planning Your New Garden
How to Design Your New Garden
Managing the Parkway
Greywater