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Whether you’re looking to make your landscaping more eco-friendly, trying to save money on water bills or hoping to prevent flood damage, adding a rain garden could be a great option, experts say. Some cities and regions even have offered incentives for residential rain gardens meeting their standards. Palo Alto residents, for example, can receive a rebate for adding a rain garden. (The garden must be installed by a licensed contractor and inspected by City of Palo Alto Watershed Protection staff. The rebate also must be applied for before the garden is installed.)
Reasons for rain gardens
Natural filters
At its heart, a rain garden is “just a water catchment, an area of your garden where you can channel water to allow it to percolate into the soil,” said Corey Andrikopoulos, the garden director of the Elizabeth F. Gamble Garden in Palo Alto. “It helps water get back into the ground and keeps it on the property rather than going into the storm drains.”
Carefully selected plants and microorganisms in the soil help filter the water naturally, keeping it from rolling across sidewalks, driveways and other paved areas, picking up pollutants along the way and damaging the waterways.
“We do have such bad water pollution in the Bay Area. A lot of our native fish species are really struggling,” local rainwater harvesting specialist Chris Corvetti said. “Being able to help reduce polluted runoff by reducing the amount of runoff from our individual properties really makes a difference in the long run to the health of these creeks and the Bay.”
Groundwater rechargers
And in a drought-prone region, every drop can count.
“People may not realize that in a lot of places the underground aquifers have been very badly depleted,” said Shelkie Tao, a South Bay landscape designer whose company, Water Efficient Gardens, specializes in designing low-water landscaping. “The water level has decreased a lot. It’s really alarming and not healthy.”
By building more rain gardens, she said, “more rain water can go back and recharge that groundwater so we have more water in the ground in the future when we have another megadrought.”
For residents, rain gardens come with additional benefits. Gardening with drought-tolerant native plants (especially when replacing a lawn) reduces the amount of irrigation water needed to keep a yard flourishing. Rain gardens also can help combat flooding by drawing water away from buildings. When done right, rain gardens are both attractive and useful, experts say. They can be an excellent way to support the environment — a landscape system that works holistically to benefit everyone.
Rain garden basics
The specifics of each rain garden vary, Andrikopolous said. The basic essentials are a low-lying bioretention basin (usually lined with gravel or pebbles in addition to healthy soil), suitable plants, and a way for runoff water to be channeled there (a downspout extension or a swale, for example).
The necessary size of the rain garden depends on the amount of runoff it will be absorbing. He recommended choosing a sunny, non-soggy spot and paying attention to the yard’s slope and the type of soil available, amending it with compost as needed. Gardens with sandier, well-draining soil can use a smaller retention area while clay soils drain more slowly and require a larger area.
Size & location
When considering adding a rain garden, “I would say the location of the downspouts is the number one factor,” Tao said. “Number two is space: A rain garden must be at least 10 feet away from the base of the house.” It also should be 5 feet from property lines, and 3 feet from public sidewalks, according to the city of Palo Alto. It should avoid trees (they don’t generally like their roots being inundated, or damaged by digging), septic areas and shallow utilities, too. The water in a sucessful rain garden stays there only for a short time until it can soak into the soil, no more than a day or two, so mosquito larvae should not be an issue if it’s functioning properly.
The right plants
There are plentiful options for native plants that work well in rain gardens, adapted as they are to California’s Mediterranean climate of wet winters and dry summers.
“I would heavily recommend native plants for these kinds of plantings. They naturally handle this wet/dry cycle. This is a system that is going to be inundated entirely at some points but most of the year be dry,” Andrikopoulos said.
Toward the center of the rain garden, he recommended rushes and sedges: plants such as scouring rush, creeping wild rye, basket rush and torrent sedge.
“They can handle dry sun and handle that inundation once in a while,” he said. “As you’re getting out toward the more drought-tolerant areas, ceanothus (California lilac), California fuschia and yarrow work well, sages work well.”
Native plants are also immensely beneficial for wildlife — supporting and attracting the critters essential to a healthy ecosystem.
Local inspiration
Gamble Garden
Gamble Garden has had a rain garden for the past five years, planned and installed with the help of Grassroots Ecology (which also has helped install other local rain gardens). The rain garden at Gamble captures water runoff from the parking lot and also has a water catchment system connected to the roof of the adjacent building, which can be used for irrigation as needed. Grassroots Ecology also recently teamed up with other nonprofits including Climate Resilient Communities to install rain gardens at homes in East Palo Alto as part of a flood mitigation effort.
Professional designers
Professional landscape designers with rain garden expertise are available, including Tao, who got into the gardening business after she had her own challenging experience converting her lawn into water-efficient landscaping. She built waterefficientgardens.com originally as a resource platform for other residents like her, then went on to complete Foothill College’s Environmental Horticulture & Design program with honors. Tao offers a variety of online landscape design packages, can recommend contractors for installation and, for an extra fee, she will even handle the whole rain garden rebate process for clients in qualifying cities.
Corvetti works in Santa Clara and San Mateo counties with organizations including Grassroots Ecology, Bay Area Water Supply & Conservation Agency (BAWSCA), and Flows to Bay (San Mateo County’s water pollution prevention program), educating the community on the benefits of rainwater harvesting (check their websites for upcoming spring classes and workshops).
“The biggest cost, if you want to do it on your own,” she noted, “is time.” It does take effort to dig, plus the planning and know-how to do it right. Adding gravel and mixing compost with a yard’s native soil can be done very cost effectively, with the gravel costing just around $30-$50 and compost often available for free, she said. The plants will be an additional cost.
To make your rain garden a success, provided your yard meets the right conditions and you follow best practices, “I think a lot of it comes down to site preparation and selection,” Andrikopoulos said. “Doing that work up front, of understanding how the water’s going to channel, understanding the soil in your yard, there’s nothing you can’t really work around as long as you do your homework up front and plan it out,” he said.
Resources
- Coastal California Rain Gardens (from University of California Agriculture and Natural Resources)
- Rain Gardens (Flows to Bay program)
- City of Palo Alto’s rain garden rebate program
- Grassroots Ecology’s demonstration gardens
- The Watershed Watch Campaign, an initiative of the Santa Clara Valley Urban Runoff Pollution Prevention Program (SCVURPPP)
