How to Design a Rain Garden in Austin, Texas

Austin, Texas is definitely one of those cities that sticks with you no matter the length of time you spend there. From the eclectic collection of shops, amazing food down every main street and back ally, or the legendary Texas hospitality and charm, Austin really lives up to the hype of its tongue in cheek motto ‘Keep Austin Weird’ in more ways than are obvious to the casual observer. Being a center for creative design and out of the box thinking, Austinites have embraced the idea of getting innovative when it comes to the way they view landscaping and water management. One of these ways is with the healthy use of Rain Gardens. Although the use of rain gardens, bioswales, and other forms of using the landscape to manage rainwater have gained in popularity in the past years, it is good to know the basic fundamentals of what makes for a successful rain garden that can withstand the extremes of the Central Texas climate.

First Things First: What is a Rain Garden?

A Solid Foundation. Let’s start by defining what exactly is a rain garden. There are lots of terms and descriptors used to categorize these very similar landscape applications, but they all differ from each other in one way or another. A rain garden is perhaps the simplest of them all. A rain garden is purely an area of planting that you install in a low spot in your landscape. Rain gardens should be designed to hold water for only a brief period of time after a storm, with water quickly infiltrating back into the ground.

Unlike a pond or wetland, rain gardens should not generally be more than a foot deep at any given point and should not use any sort of liner. The actual depth and size of your rain garden will vary depending upon how much rainfall you need to collect from your roof or other impervious surfaces.

Below are examples of a rain garden in a dry state versus a wet state.

A Residential Rain Garden in a Dry State

A Residential Rain Garden in a Wet State

Benefits of Rain Gardens

Small plantings packing a BIG punch.  The benefits of rain gardens are multifold. Firstly, they help prevent pollution from runoff water. The water that falls off our roofs, down the street, or across a parking lot isn’t pure rainwater; it collects pollutants as it flows, especially excess nitrogen and phosphorus from lawn fertilizers. These pollutants can harm rivers and ponds by causing algae blooms and fish kill. The deep roots of native plants readily absorb these nutrients, protecting groundwater quality. During heavy to moderate rain events, this storm surge can cause damaging erosion, sediment buildup, and bring a number of other harms to freshwater ecosystems, negatively impacting freshwater mussels and other aquatic life.

Rain gardens can also play a part to protect Austin properties from floods. A mature stand of rain garden plants will take up excess water that might normally puddle in your yard, leading to water damage issues in your home. When you get rid of standing water, you also reduce mosquito breeding problems around your home.

Rain gardens create habitats for wildlife. The traditional Austin front yard is turf grass, a monoculture that does little to nurture wildlife, but a mixed planting of native Texas flowers and grasses will draw butterflies, bees, beneficial insects, and birds. Rain gardens also help conserve water. Once established the native plants that thrive in the rain garden won’t need supplemental irrigation, as they are deep-rooted and have evolved to survive periods of drought between rains.

The Right Site, Size, and Shape for the Rain Garden

Getting specific.  How big should a rain garden be? A small rain garden is better than nothing, but you should plan on a garden at least 150 square feet in order to include an interesting variety of plants that can process the runoff associated with your landscape. Choose a natural, rounded shape for your rain garden, like an oval, teardrop, or kidney shape. Outline the potential area with a hose or rope first, and view it from all angles, as well as from inside your home to envision the finished product.

If you’re planning to divert your roof gutters into your rain garden, you won’t want to install the feature too far away from your home, but you must place it at least ten feet away from your home. Underground utilities and tree roots may also influence the placement of the rain garden.

Be sure to check for these two things before you begin to dig.

1. If your yard doesn’t have a natural depression, you will need to create one by digging: either by hand or with an excavator. It isn’t necessary to create a pit; a gentle basin no more than about five inches deep is sufficient. The basin should have a flat bottom and gently sloping sides, and you can use some of the fill dirt to create a berm to hold excess rainfall until the plants can absorb the excess water.
2. Additionally, the use of river rocks 2”- 4” diameter can be implemented to help slow the flow of water entering the planted rain garden and add textural interest.

Plants for a Rain Garden

Choosing the Right Plants.  In order to properly design a rain garden, only use perennial plants. This is because a rain garden functions as a water remediation (cleaning) feature and greatly depends on the deep roots of perennial plants. When considering plants, look at their soil moisture requirements and plan accordingly. While your rain garden should favor plants that can tolerate occasional flooding, this does not mean you are limited to only wetland species or that they are necessarily the best fit for a rain garden. In places like Austin, where rain may be seasonal or intermittent, drought tolerance should be a greater consideration than tolerance of flooding. Luckily, Austin native plants with deep roots that are useful for driving water back into the earth are often drought tolerant as well—making them an excellent choice for rain gardens.

Here are a few good choices of plants for each zone of a rain garden that are well suited to Austin:

Base of the garden

• Frog Fruit
• Mistflower
• Milkweed
• Eastern Gamagrass
• Horsetail

Sides of the Garden

• Big Bluestem
• Big Muhly
• Black-eyed Susan
• Cut-Leaf Daisy
• Coreopsis
• Gulf Coast Muhly

Trees and Shrubs for a Rain Garden

Add Some Height. Although a rain garden is not the place to grow a large shade tree, you can add a small ornamental tree or shrub to act as a focal point in the landscape. A Texas redbud tree has beautiful pink-red flowers in the spring and will reach a mature height of 15-20 feet. A cypress or cedar elm specimen can work in a larger landscape, and will greatly increase the water absorption ability of your rain garden. Trees also lend much-needed shade along a street or sidewalk when rain gardens are used in those settings.

Rain Garden Care and Maintenance

Create a long life for your garden. Although rain gardens are lower in maintenance than a typical Austin residential flowerbed, they definitely will benefit from some of the same basic landscape care practices. The plants in rain gardens will require more direct care in their first year after planting as they establish their root systems. Be sure to remember to water deeply but infrequently during times of drought to encourage healthy roots to grow deep into the soil.

Rain gardens need to be kept free of weeds, both for plant health and aesthetic value. The best time to weed is right after a strong Austin rain event when the soil becomes soft and weed roots release their hold more easily. Additionally, by adding a  three-inch layer of mulch on top of the soil surface weed growth will be further suppressed. Use a fine hardwood mulch, as it’s less likely to float away after a heavy rain.

Diagram of water flow from a rooftop to a rain garden

Top Photo: Source

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