Rain gardens are simple landscaping features used to slow, collect, infiltrate and filter storm water. They offer a great way to turn a landscape “problem” into a real benefit. Rain gardens are planted areas—best added to a low lying area that collects rain water—that include deep-rooted native plants and grasses that are designed to thrive in wet soil, soak up excess rain water, and withstand intermittent dry periods.

There are aesthetic benefits to rain gardens as well, transforming a bare, wet area into a green, blooming habitat that provides food and shelter for birds, butterflies, and other wildlife. Amphibians such as frogs and toads will be attracted to this naturally wet area.

The problem

Increased stormwater runoff is the real problem. Add soil erosion to that and the result is vulnerability to flooding. Rain gardens help prevent both, helping to conserve water and soil.

Consider the water cycle shown above and then add human development to the picture. Humans create stormwater runoff when natural areas are developed, replacing them with a sea of impervious surfaces fragmenting our green spaces.  Within a developed residential area, pollutants such as fertilizers, herbicides, pet waste, and oil are washed from lawns, streets, and parking lots into local streams and drainage systems.

Polluted runoff is the number one water
quality issue in the United States. 

How rain gardens help

While a single rain garden may seem inconsequential, it has great value, and several in a neighborhood collectively can produce substantial benefits. They slow the water down and let it collect in the garden’s depression, settling soil, silt and organic material that are washed by the water from higher ground. Water slowly filters back into the soil where it is needed most.  The deep rooted plants and grasses in the rain garden hold of the soil, keeping it in place. Rain gardens can also be designed to divert run off from sewer systems.

Plants within the rain garden increase the infiltration of water, giving the natural process that removes pollutants time to do its work. Naturally purified water then recharges the groundwater system. The end result is that by adding a rain garden to the landscape is a strategy that makes a difference.  Flooding is reduced.  Pollutants are filtered from the water. Runoff is diverted from streets and storm sewers.

Concern that a rain garden might serve as a breeding area for mosquitoes is not valid when they are sited correctly. Following a rain, ponding should last no longer than approximately 72 hours. This is a much shorter time frame than the 7 to 14 days required for most species of mosquitoes to develop and hatch from eggs laid in standing water.

Rain garden basics

Choose a site. Locate your garden in a low lying area of your landscape that tends to collect rain water at least 10 feet from your foundation. Choose a sunny or partially sunny spot. Also consider how it can be incorporated into your existing landscape replacing an area of traditional turf grass where the lawn slopes toward the street. An area that would catch roof run off or water from a down spout is perfect. If the rain garden is located on a slope, create a berm on the low side to retail water and soil.

Compared to a patch of lawn, a rain garden allows 30% more water to soak in the ground.

Test drainage. Test the location’s drainage before you create the bed. Dig a hole 8 to 12 inches deep and fill the hole with water. The water should soak in within 48 to 72 hours. Soils heavy in clay will drain much more slowly than soils heavier in loam, silt or sand. Amend sites heavy in clay with organic compost to improve the soil and help drainage. If the site doesn’t drain within 72 hours, choose another site.

Start digging. Rain gardens can be any size, but a typical residential rain garden ranges from 100 to 300 square feet. The depth of the garden can range between four and eight inches. Anything too deep might pond water too long and if too shallow, it will require greater surface area to effectively manage water.

Add plants. Choose a variety of native forbs and grasses, planting those with higher water tolerance in the middle of the garden. Include plants of varying heights and bloom times to maximize the garden’s depth, texture and color. Plant in groups of three to seven plants of a single species.  Go for diversity. In natural areas, a diversity of plant types not only adds beauty, but also creates thick underground root network that keeps the entire plant community in balance.

The chart below includes plants for our area suitable for a rain garden. Planting zones are indicated as:

Margin: the high edge around the rain garden that is the driest zone
Median: the area between the margin and center
Center: the middle of the garden that is deeper and will stay wet longest

Help it flourish. Rain gardens can be maintained with little effort after plants are established. Weeding and some watering during dry periods will be needed the first two years.

Attend the upcoming rain garden class

Join Patrick Dickinson, Texas A&M Water University horticulturist on Saturday, October 27, 2018 from 9:00 a.m. to noon as he presents Gardening 102:  Rain Gardens.

Register here.

Resources

Refer to Harris County AgriLife Extension gardening fact sheet, Rain Gardens, for more details about planning a rain garden and for a full plant list.

Check out WaterSmart, a presentation by Chris LaChance of Texas AgriLife Extension, for good information and nice photos of various rain gardens.

This how-to manual on Rain Gardens by the Wisconsin Department of Natural Resources may have plant lists that aren’t suitable for this area, but it’s a good guide to creating a rain garden no matter where you live.