Rain gardens

Now that wet weather has finally arrived, it seems a good time to write something about those little drops falling from the sky.

You might ask, “What are rain gardens?” One writer has very aptly described them as gardens that “encompass all possible elements that can be used to capture, channel, divert and make the most of the rain and snow that fall on a property.” The goal is to create a landscape that keeps water onsite. Rain gardens are not ponds, however; when properly designed, they allow water to percolate into the soil within one to three days.

Why is water retention important? Consider this: urban/suburban development has covered vast areas of land with paved surfaces and buildings, preventing any precipitation from reaching the soil underneath. The moisture that used to soak into the soil now drains away. It can no longer nurture the roots of trees and others plants, benefit soil-dwelling organisms, or help sustain natural underground reservoirs of water.

Most city rainfall travels from sky to impermeable surface to storm drain.  Rain from waterproof roofs is collected in rain gutters, then it travels through drainpipes to street gutters. Rain that falls on parking lots, streets, and sidewalks flows into storm drains without ever touching bare soil. Those storm drains connect to conveyance systems that carry untreated water into local waterways. Street pollutants (oil, gas, asphalt leachates, antifreeze, and more), loose trash, and many other harmful substances are thus carried out to local rivers and the ocean. That sobering fact is why many of our local storm drain inlets are painted with notices that say, “No Dumping. Flows to Delta.” Even the water that drains from lawns can be contaminated with excess fertilizer, pesticides, and pet waste. Untreated, polluted runoff fouls natural bodies of water, harms aquatic wildlife and vegetation, and is a main cause of toxic algae blooms.

Rain gardens can help mitigate these problems by restoring habitat and mimicking natural patterns of water movement. They are key elements of sustainable landscaping and have many environmental benefits:

  • They capture and conserve precious rainwater and snowmelt rather than diverting it to storm drains.
  • They help recharge depleted stores of groundwater by allowing more water to soak into the earth.
  • They help to minimize erosion and flooding
  • They reduce water pollution, since they give plants and soil microorganisms the time to break down water-borne toxins
  • They minimize the need for supplemental garden irrigation

While fulfilling all these utilitarian purposes, rain gardens can also be beautiful additions to home and commercial landscapes. Local native plants are best suited

The simplest rain garden is a well-drained depression with amended soil or gravel at the bottom. More complex rain garden designs can include rain barrels or cisterns to capture runoff from roofs; bioswales or “dry creek beds”; pervious paving (which is porous and allows pass-through of water), and infiltration galleries (perforated below-grade conduits for water transfer).

Rain gardens all have two elements in common: (1) the water enters at a grade higher than where it settles, and (2) there is an overflow outlet. From there, the possibilities are endless. Rain garden designs and plantings can be modern, classical, or rustic. They can either be concealed or they can be featured elements of a landscape design.

Rain gardens should be placed at least 10 feet away from homes. They should be located in an area with good drainage, and kept away from septic systems, underground utilities, and the roots of large or established trees.

The entry sign at the Elk Grove Rain Garden Plaza (Photo © Kathy Ikeda)

For a wonderful outing and a comprehensive overview of how a well-designed rain garden functions, visit the Elk Grove Rain Garden Plazaat 9385 Laguna Springs Drive. It features an interactive sculptural fountain surrounded by different types of permeable paving; a raised composite wood boardwalk over a sunken wetland area; a garden planted with locally-sourced, low-water-use California natives and Mediterranean plant species; a shade structure fitted with rain chains and rain barrels; a large paver patio with bench seating; a dry well for groundwater recharge; and many artistic elements, including a low wall inset with colorful, student-designed ceramic tiles. A fact sheet and plant list for this garden are available online.

One part of the City of Elk Grove’s Rain Garden Plaza, with the shade structure and fountain in the background and a small portion of the landscaped bioswale area in the foreground. (Photo © Kathy Ikeda)
















Until you have an opportunity to visit this rain garden, enjoy exploring these articles and resources:

For gardening-related questions, call the UC Master Gardener office at 209-953-6112, or visit our website.




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