Rain to Table

Part 2 of a 3-part series. Growing native plants—and native foods —with rainwater.

May 8, 2017

HomesteadIssue 24: May/June 2017

Installing a rain garden should be a rite of passage for living in the Sonoran Desert. When you do, you’ll transition from a city dweller to a desert dweller taking part in the intricate web of water, soil, plants, and wildlife that make our desert community distinct.

Someday soon, rain gardens will be the essential, basic infrastructure of any landscape in Baja Arizona. If you install a rain garden in your yard today, you may be the first on your street. But then sit back and watch other basins, berms, and swales pop up, at neighbors’ and friends’ yards. The water-harvesting mania catches on quickly, and for good reason. It makes sense, and we get instant gratification when rainfall soaks into our basins to grow lush native gardens.

If you take a walk in the Sonoran Desert, you will see a rich diversity of trees, shrubs, wildflowers, and groundcovers thriving in a wild setting. These plants grow on rainfall alone. Picture your yard. What native diversity could thrive on rainwater? Rain gardens provide the structure for water to be captured and naturally irrigate your plants. It is the most inexpensive and practical form of water harvesting, so it’s a great starting point. Rain gardens are also an effective way to harness rainfall to grow native edibles and tap into local abundance for your table.

I’ll give you some basic pointers in this article. To learn more, consider attending a rainwater harvesting rebate class with Watershed Management Group or Pima County Cooperative Extension/Smartscape Program. By attending this class you also qualify to receive Tucson Water’s rainwater rebate—up to $500 for rain gardens.

There are four basic principles to keep in mind when planning a rain garden:

      1. Rain gardens need plants to work.
      2. Rain gardens need mulch. Organic is best.
      3. Make ’em big! Capture as much water as possible. Your soil can store a lot of water.
      4. Rain gardens should reduce your water use, not increase it.

Plants are a functional element of rain gardens, just like the soil, mulch, and structural rocks or pipes. In order to infiltrate rainwater, you need plant roots in the ground to create space for the water to move through the soil. They create a living system in concert with the soil, organic materials, and microbes, also known as the soil food web.

Landscaping with native plants is a great way to increase wildlife habitat and extend the Sonoran Desert into the urban environment. But in the spirt of our theme, Rain to Table, let’s step it up and choose native plants to create a food forest. You can have your shade and eat it, too. Plant a mix of native shade trees with edible beans or pods (velvet mesquite, blue palo verde, desert ironwood). Then plant your midstory shrubs featuring plants like wolfberry, desert hackberry, chiltepin, oreganillo, and cholla. Fill in your groundcovers with native wildflowers to add color and fun.

Native bunch grasses are an important plant to place in basins. Though not edible, they help create a porous, organic soil to soak up and infiltrate with their dense root system, and they don’t mind being flooded by water.

If you do nothing else, use organic mulch in your yard and apply liberally. The mulch is an important element in a rain garden, helping protect the soil from erosion, reducing evaporation of moisture in the soil, and adding organic material into the soil. The best organic mulch is what is produced at your own house, from your own plants. So start by allowing organic material to stay on your soil and prune materials and drop them in your basins. You can also get free organic material from tree-trimming companies or purchase it from local companies like Tank’s Green Stuff.

Make those basins big. This doesn’t just mean deep. You want them to have substantial capacity so you can make them broad as well. Basins will fill in with organic debris, so you’ll want to make them larger so they have substantial capacity over time. There will often be more water than your basin can handle, so you need to plan for safe, controlled overflow. Make sure to direct your overflow if possible to another landscape area, instead of a hardscape or the street.

Finally, one of the main purposes of a rain garden is to reduce water consumption. By harvesting rain, you can irrigate your plants with rainwater instead of municipal water or well water. When you first add plants, they will need more regular irrigation to get established. Consider a temporary irrigation system, instead of investing in a drip irrigation system that stays on indefinitely. Time the planting of your rain garden in the fall to benefit from winter rains for establishment.

The good news is rain gardens are affordable to install. At the most basic, you can create the rain gardens yourself by hand-digging. Find a source for free organic mulch and you can save money with native seed mixes or bartering for plants. Of course, if you have a budget, you can hire a contractor. There are a handful of great companies in Baja Arizona that can design and build a native rain garden for you. But whether you do it yourself or hire a contractor, you should know the basics, to make sure it’s done right.

Passive Rainwater Harvesting: Earthworks 101

Basin: An earthen depression designed to collect and infiltrate rainwater.

Berm: A raised earthen mound, often crescent shape, laid on contour, designed to slow surface runoff and increase infiltration.

Swale: An elongated earthen depression with a shallow slope designed to infiltrate and transport rainwater runoff.

Mulch: Material used as a surface cover for soil to reduce erosion and evaporation. Organic mulch is made up of plant materials, and inorganic mulch is usually made of rock.

Native plant: A plant that is indigenous or naturalized to a region over a given period of time.

Inlet: Where rainwater enters earthworks.

Overflow: Where rainwater exits earthworks when full.

This is the second article of our Rain to Table series. If you missed the first article, visit EdibleBajaArizona.com to learn about local water budgeting and join the Rain to Table campaign at WatershedMG.org/RainToTable. Using a simple local water budget calculator, you can determine how much rain you can harvest at home to plant your own rain garden. ✜

Lisa Shipek is the executive director of Watershed Management Group.

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