Waterwise: A how-to guide to a rain garden
- Rain gardens are landscaped areas planted with wild flowers and other vegetation that soak up rain water coming from a roof, driveway or other surfaces.
- A typical residential rain garden ranges from 100 to 300 square feet.
- A typical rain garden is between four and eight inches deep.
Note: This is the second of two articles from Master Gardener Nancy Hawkins on suggestions for uses of water from the predicted rain this winter.
A new solution I have been reading about lately is a rain garden. On a recent Master Gardener tour of the Cal Poly, SLO arboretum, the docent showed me an example of a rain garden. Rain gardens are similar to retention basins, but smaller. They are landscaped areas planted with wild flowers and other vegetation that soak up rain water coming from a roof, driveway or other surfaces.
In a storm, the rain garden fills with a few inches of water which slows the flow of water over the surface of the landscape, thus increasing infiltration of water into the water table while filtering the water and reducing pollutants. Water soaks into the ground rather than running off into storm drains. Compared to a conventional patch of lawn, a rain garden allows about 30 percent more water to soak into the ground.
Rain gardens produce substantial neighborhood and community environmental benefits. Rain gardens work for us in several ways:
• Increasing the amount of water that filters into the ground, recharging local and regional aquifers.
• Helping protect communities from flooding and drainage problems.
• Helping protect streams and lakes from pollutants carried by urban storm water.
• Enhancing the beauty of yards and neighborhoods.
• Providing valuable habitat for birds, butterflies and insects.
Home rain gardens can be in one of two places: near the house to catch only roof runoff or farther out in the lawn to collect water from the roof and other hard surfaces and the lawn. The rain garden should be integrated into existing and future landscaping. It should be located at least 10 feet from the house so water doesn’t seep into the foundation, in full or partial sun, and in a level part of your yard.
Any reasonably-sized rain garden will provide some storm water runoff control. A typical residential rain garden ranges from 100 to 300 square feet.
Planning for a rain garden
A typical rain garden is between four and eight inches deep. One more than eight inches deep might allow water to stand too long, look like a hole in the ground, and present a hazard for someone stepping into it. A rain garden less than four inches deep will need an excessive amount of surface area to provide enough water storage to handle the runoff from larger storms. No matter what the depth of the rain garden, the goal is to keep it level. The slope of the yard should determine the depth of the rain garden.
After choosing the depth of your rain garden, identify the soil type — sand, loam or clay. Sandy soils have the fastest infiltration, clay soils have the slowest, and loamy soils are in the middle.
The next step in choosing your rain garden size is to find the area that will drain to the rain garden. As the size of the drainage area increases so should the size of the rain garden.
Digging the rain garden
While digging the rain garden to the correct depth, heap the soil around the edges to create a berm. The berm will need to be highest at the downhill side, becoming lower on the sides and gradually taper off by the time it reaches the top of the rain garden. In a garden with a slight slope, there should be plenty of soil from digging out the rain garden to use for the berm. After shaping the berm into a smooth ridge about a foot across, compact the soil. The berm should have very gently sloping sides; this helps smoothly integrate the rain garden with the surrounding landscape and also makes the berm less susceptible to erosion.
Planting the rain garden
Planting a rain garden is the fun part. An appealing variety of native wildflowers, ferns, grasses, shrubs, and trees thrive in moist soil. Your rain garden can be divided into three wetness zones. In the lowest zone, plant species that can tolerate short periods of standing water as well as fluctuating water levels. Species that can tolerate extremes of wet soils and dry periods are appropriate for the middle zone. Plants that prefer drier conditions go along the outer edge of a rain garden.
Use as many native California or compatible Mediterranean plants as possible. When finished planting, add a three-inch layer of an organic mulch to suppress weeds.
Changes to Visalia’s outdoor watering schedule
Outdoor watering will be prohibited over the next three months in Visalia.
The water-saving move comes as the winter schedule became effective on Dec. 1 and lasts until February.
“While the recent rains and forecasted El Niño winter should help to replenish out water resources, it will take more than one good winter to recover from four years of exceptional drought,” said Kim Loeb, Visalia Natural Resource Conservation manager.
There are exceptions to the watering schedule. Watering of shrubs, trees or vegetables is allowed using a watering can or hose fitted with a shut-off nozzle. Car washing is also allowed with a hand-held bucket or a hose with a shut-off nozzle.
Visalia residents are encouraged to continue conserving water, following the city ordinances.
Washing of sidewalks, driveways or other paved areas is prohibited, unless it is necessary for the health and safety of the public. Use of low-flow, high pressure washer is required. Water runoff is prohibited.
Washing off buildings is also prohibited, unless preparing for the building for sale or painting. Use of a low-flow, high-pressure water is required. Runoff is prohibited.
In Tulare, there is no outdoor watering in December and January.
Waterwise is a news and notes column Reporter Luis Hernandez compiles. Send Waterwise ideas and suggestions to the reporter on Twitter @lfhernanvtd.