How to Build a Rain Garden
A rain garden can help beautify your yard and help protect the environment. Think of the garden as a shallow bowl, about 6 to 9 inches deep, that captures rainwater from your roof, sidewalks and driveway. The rain garden allows you to slow down the flow of stormwater entering our waterways, to soak up some pollutants and filter the runoff that would otherwise end up in a storm drain, and ultimately in our creeks and rivers.
The garden might be most ideal in your front or backyard depending on the amount of sunlight. Full sun is best. Make sure your rain garden will be at least 10 feet from your home, backyard fence, or any other building. Avoid underground utility lines, a septic system, or tree roots you don’t want to damage when digging. Before you start digging your garden, you will want to do what’s called a percolation (“perc”) test to see how quickly water soaks into your soil.
Rain gardens may be used in the Edwards Aquifer Contributing Zone to treat stormwater for increased quality and to reduce flows off the property. However, rain gardens must either be lined with an impermeable liner or be part of a treatment train of BMPs if installed over the Recharge Zone.
Check out the rainfall during a storm. Where does it fall off the roof? Does your home have gutters and downspouts that direct roof runoff onto hard surfaces? If so, you can redirect the downspout to your lawn; this may be the perfect spot for your rain garden!
Fill it with water and let it drain.
Fill it with water a second time. If the water drains at least half an inch in an hour the second time you fill it, your soil has adequate drainage for a rain garden.
Rain Garden Blueprint
This depends on the size of your roof and the available space in your yard.
General instructions: Measure the length and width of the rooftop draining to the downspout. See diagram:
Here’s an example: to find the size of your rain garden, multiply the drainage area of the roof (¼ of the roof size) by the depth of the amount of rain water runoff coming from your downspout or roof top (typically, one inch to 1 ½ inches of runoff) for irrigation.
- If we calculate, here’s how it would look: 60′ (length) x 30′ (width) = 1800 square feet
- If the drainage area is ¼ of that size—it will be 450 ft.
- 450 divided by 6 (depth of garden) gives you the size of the rain garden: 75 sq. ft.
- Remember, it’s not one size fits all. Take a look at our chart to determine what dimensions might work best in your yard.
Grab a water hose or some string and maybe some wooden stakes, or flags for markers, to help outline the rain garden.
Typically shaped like a kidney bean, your rain garden dimensions could be 20 ft. x 10 ft. for the 200 total square foot project. Dig your rain garden about 9 inches from the top of the soil, within the area you’ve outlined. Be sure to gently slope the sides of the garden to make a gradual fall. Remember it is a shallow bowl or basin.
Digging and Planting
A shovel will do. Begin digging inside the boundaries you’ve outlined or flagged.
Plant list for Bexar County can be found here.
Plant list for Wilson, Karnes, and Goliad Counties can be found here.
Water the plants just until they are rooted or established in the ground. Replace plants as needed. Remove any litter or debris that accumulates after a storm event. We want the rain garden to serve two purposes: to beautify your yard and organically treat pollutants to help the environment.