How to Make a Rain Garden: Step-by-Step Guide

A rain garden is one of the most effective ways to manage stormwater runoff while adding beauty and biodiversity to your landscape. Designed to collect and absorb rainwater from roofs, driveways, patios, and other hard surfaces, rain gardens help reduce erosion, improve drainage, and create habitat for pollinators.

For homeowners in the St. Louis area, a rain garden can be especially beneficial for managing heavy rainfall and reducing standing water in low spots around the property. With the right location, soil preparation, and plant selection, a rain garden can become an attractive, low-maintenance feature that benefits both your landscape and the environment.

Key Takeaways

• Rain gardens capture and absorb stormwater runoff before it leaves your property.
• Proper site selection, soil preparation, and plant selection are critical for success.
• Native plants help create a beautiful, low-maintenance garden that supports pollinators and wildlife.

What Is a Rain Garden?

A rain garden is a shallow, landscaped depression designed to temporarily collect rainwater and allow it to slowly soak into the ground. Unlike a pond, a rain garden does not hold water permanently. Instead, it captures runoff after storms and allows the water to infiltrate the soil naturally.

Rain gardens are often installed near downspouts, roof leaders, driveways, or other areas where stormwater flow is concentrated. They help reduce runoff, fix drainage problems, minimize erosion, and add visual interest to the landscape.

Step 1: Choose the Right Location

The first step in creating a rain garden is selecting an appropriate location. Look for areas where runoff water naturally collects or where a downspout can be redirected.

Rain gardens should generally be placed at least 10 feet away from your home's foundation and away from septic systems or utility lines. You'll also want to consider nearby sidewalks, property lines, and the overall grading of the landscape.

Low areas often work well, but avoid locations with high groundwater or areas that remain constantly saturated. A properly placed rain garden should collect water temporarily without creating standing water problems.

Step 2: Test and Prepare the Soil

A rain garden is only effective if water can move through the soil efficiently.

Before digging, perform a simple drainage test by excavating a small hole and filling it with water. Observe how quickly the water drains. If the water remains for an extended period, the soil may need improvement.

Many rain gardens benefit from adding compost, sand, or topsoil to improve soil structure and infiltration. This helps create a permeable soil mix that supports healthy root development while allowing runoff to soak into the ground.

Step 3: Determine the Size and Shape

The size of your rain garden depends on how much runoff it will receive.

Factors such as roof size, driveway area, soil conditions, and drainage patterns all influence the required capacity. Most residential rain gardens range from 100 to 300 square feet, although larger or smaller installations may be appropriate depending on the site.

Step 4: Dig the Basin

Once the layout is marked, it's time to create the basin.

Most rain gardens are excavated to a depth of approximately 4 to 8 inches, depending on site conditions and expected runoff volume. The goal is to create a shallow depression with gently sloping sides and a level bottom surface.

As you excavate, keep in mind how water will enter and move through the garden. The basin should allow water to spread evenly rather than concentrate in one area.

Step 5: Create a Berm and Overflow Area

To keep water within the garden long enough for infiltration, many rain gardens include a berm along the downhill edge. This small raised mound helps contain runoff within the basin.

It's also important to plan for overflow during larger storms. Every rain garden should include a spillway or overflow pathway that allows excess water to safely exit the garden when rainfall exceeds the garden's capacity.

Step 6: Select Native Plants

Plant selection is one of the most important parts of rain garden design. Native plants are typically the best choice because they are adapted to local growing conditions and develop deep, well-established root systems that improve soil infiltration. They also provide valuable habitat for pollinators and wildlife.

Popular St. Louis native plants include blazing star, swamp milkweed, blue flag iris, purple coneflower, black-eyed Susan, and native ferns. Drought-tolerant plants and ornamental grasses can work well along the outer edges where soil conditions tend to be drier.

Step 7: Mulch and Finish the Garden

After planting, apply a layer of mulch to help retain moisture, suppress weeds, and reduce erosion.

Mulch also gives the rain garden a finished appearance while helping new plants become established. Decorative stone or natural rock accents can be added if desired, but avoid materials that interfere with water infiltration.

If landscape fabric is used, select a permeable product that allows water to move through the soil profile.

Ongoing Maintenance

Rain gardens require relatively little maintenance once established, but some routine care is necessary.

During the first year, monitor how water moves through the garden and ensure plants are receiving adequate moisture while roots become established. Remove weeds as needed and replace any plants that fail to survive.

Long-term maintenance may include:

• Refreshing mulch
• Pruning old growth
• Removing leaves, branches, and excess debris
• Monitoring the inlet and overflow areas
• Replacing plants when necessary

Over time, the garden should become more self-sustaining as root systems mature and plant coverage increases.

Additional Considerations

Before starting a rain garden project, take time to evaluate your property's drainage patterns and runoff sources. Understanding where water comes from—and where it goes—can help you design a more effective solution.

For larger properties or sites with significant drainage challenges, hiring a professional landscape architect may be beneficial. Features such as retaining walls, drainage systems, and grading improvements can sometimes be incorporated alongside a rain garden to improve overall stormwater management.

Combining Beauty and Function

A rain garden is one of the few landscape features that can improve drainage, support pollinators, reduce runoff, and enhance curb appeal all at the same time.

By carefully selecting the location, preparing the soil, and choosing native plants, homeowners can create a sustainable landscape feature that provides long-term environmental and aesthetic benefits.

At Poynter, we help homeowners throughout the St. Louis area design landscapes that are both beautiful and functional. Whether you're interested in a rain garden, more in-depth drainage solutions, or a complete landscape renovation, our team can help create a solution tailored to your property.

Contact us today to schedule a consultation.

FAQs

Where is the best place to put a rain garden?

The best location is a low area where runoff naturally collects, such as near a downspout or drainage path. Rain gardens should generally be located at least 10 feet from your home's foundation and away from utility lines or septic systems.

How do you build a simple rain garden?

A simple rain garden starts with selecting the right location, testing soil drainage, digging a shallow basin, creating an overflow area, planting native species, and applying mulch. Proper sizing and drainage are essential for long-term success.

What is needed for a rain garden?

A rain garden typically requires a shallow basin, permeable soil, compost or soil amendments, native plants, mulch, and a safe overflow pathway. Depending on the site, drainage pipes, berms, or decorative rock may also be incorporated.