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The Dry Garden: How to capture rain

October 7, 2011 |  8:00 am

Rain dog
With the first rain of the season comes a question: How best to capture it for the garden? There is no single answer. Each property has dramatically different opportunities and challenges. Get it right and rainy season becomes a time of unrivaled beauty and pleasure. Get it wrong and you can ruin your house, or your neighbor’s.

TreePeople have a good basic guide.  Across much of the Los Angeles basin, water can be banked by following the basic recommendation to direct plastic gutter extenders into planting beds. Take care that the grade of the garden slopes away from the foundation of your house. It is not a good idea to inundate the footing of a structure.

The harder the ground, the slower absorption, but the bonus for properties with clay soil is that once the rain settles, the earth will hold this water for months. You can increase the infiltration by creating pond- or creek-like swales, then landscaping the area with native plants such as oaks, toyon and ceanothus. The banked water should be available to plants through spring, with little supplemental irrigation needed when the plants go dormant in summer.

Inspired by the Garden/Garden project in Santa Monica, I hired two designers -- Nick Tan of Urban Organics and Marco Barrantes, who now runs La Loma Development Co. -- to create an artful trench at my old house that would bank rain. The story of how we aimed to minimize rainy season runoff there and ended up eliminating it ran in 2006.

After moving last year, I’ve learned that this technique has limitations. My new garden is on an appreciable slope and so high up in the San Gabriel foothills that last winter I received 33 inches of rain -- about twice what fell near downtown Los Angeles. The soil isn't the wonderful water banker of clay, but sieve-like sandy loam. If I directed rainwater where it would be easiest, right next to my down-slope neighbor’s house, I could easily flood his basement.

By connecting gutters to a pipe run behind a long garden fence, I’ve calculated that roughly half of the water from the roof can safely and discreetly be discharged to an orchard behind both homes. That leaves another 10,000 gallons to capture, so, this year, it’s clear. There will be storage tanks. What size? What type? I have no idea.

Rain barrel Supporters of 55-gallon rain barrels argue that they are a gateway drug to conservation. They say 55 gallons not washed into the street is 55 gallons saved! If 1.6 million homeowners had rain barrels, that would be a lot of gallons!

This is true and admirable, but I might as well put demitasses below the downspouts. Even four rain barrels wouldn’t begin to offer the capacity I need. If an inch of rain falls, more than 600 gallons can run off the roof of my 1,000-square-foot house. That's not counting what will come off the garage. My skepticism about 55-gallon rain barrels is mild compared with that of Owen Dell, the respected author of "Sustainable Landscaping for Dummies." Fed up with a craze that he argues gives well-intentioned consumers a raw deal, last winter Dell blogged that 55-gallon rain barrels were “a washout, another delusional, greenwashed, pernicious consumer scam.”

I love the chic industrial look of the larger metal barrels used by Arizona designer Scott Calhoun and plan on investigating the ones with capacities of 600 to 1,000 gallons. The challenge here becomes where to put something that could, at its best, look like a Richard Sera sculpture garden or, at its worst, a junkyard. Tucking a big barrel next to the house strikes me as dicey. Water is heavy. A 1,000-gallon barrel could exert 8,000 pounds of pressure right next to the foundation.

As a temporary measure, a friend is lending me her children’s collapsible above-ground swimming pool. Its capacity: 5,000 gallons. It won’t win prizes for beauty, but it will give me a year to see how storage might ultimately work in the tricky spot by my neighbor's house. As I pore over references to what kind of tanks might eventually be built, the books I like best are Art Ludwig’s “Water Storage: Tanks, Cisterns, Aquifers and Ponds” and Brad Lancaster’s "Rainwater Harvesting for Drylands and Beyond." Lancaster offers a nifty calculator for measuring runoff.

Once the kiddie pool goes up, I estimate I'll still have 5,000 gallons of rain running off the roof out front. I'll consult a certified arborist before I will even think about diverting that water into a small garden dominated by a massive cedar that occasionally is subject to ferocious winds. I'll see what the expert says.

This much I know as I estimate rainwater and consider how to manage it: Although the new system must function, it also must be beautiful. Earlier in the year, as I was babbling proudly to garden designer Jessica Hall about the plan to whisk half the roof water through concealed piping to the rear orchard, she asked, “Do you want to celebrate the water?”

A strong degree of brute efficiency will clearly be necessary, but as the first rains wash into L.A. County, the answer to Hall's question is an unequivocal yes. Yes!

-- Emily Green

Green's column on sustainable gardening appears here every Friday. For an easy way to follow future installments, join our Facebook gardening page.

Leigh Adams swale ALSO:

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