How To Design a Rain Garden

‍What Is a Rain Garden?

Rain gardens, also known as bio-infiltration basins, are quickly becoming popular among homeowners because they are beautiful and viable solutions to stormwater run-off and pollution. Rain gardens are a practical method for coping with periodic flooding.

A rain garden is a landscaping feature that replaces part of your lawn to collect stormwater (rain and melting snow) that runs off your roof, driveway, and grass. The loose, deep dirt in this shallow depression absorbs and filters run-off, preventing it from entering the storm drain system and, eventually, the waterways. Rainwater and overflow from gutters can be channeled into a rain garden designed with varying vibrant and deep-rooted plants.

How to Design a Rain Garden

Materials and Tools Needed

• A selection of perennial plants
• A collection of small rocks and stones
• Sand/compost mix
• Mulch
• Shovels

Steps To Design a Rain Garden

1. Figure out a Location

Figure out where the water will come from. There are several ways for water to travel to your garden. For example, it can be carried through the overflow pipe from your rain barrel, a penetration channel lined with ornamental rocks or plants, or through an extension on the end of your downspout.

The easiest way to carry water to your rain garden is by redirecting a downspout. You can even direct more than one downspout to your rain garden, although this largely depends on the location and size of the property.

However, there are a few locations that may not be suitable for rain gardens on your property:

• Areas that have poor drainage
• Too close to the house, neighboring houses, or garage
• Uphill of a septic system and 3 meters of a septic bed
• Near steep slopes or around the property

You won’t want to have the garden too far from home if you want to divert your roof gutters into your rain garden. You should, however, construct it at least 10-25 meters away from the house to avoid the risk of water invasion.

Examine the slope of the yard using a longboard. Generally, you should have a slope of about an inch to allow the water to flow freely.  

2. Select a Layout

You will have to create a depression in your yard by digging with an excavator or by hand (if you don’t already have a natural one). You don’t have to create a huge pit; a small basin, about 5-6 inches deep, is sufficient. You can also create a berm in a low spot in the yard using the leftover dirt to store additional water from rainfall until your plants can absorb it. The water is then absorbed through the network of deep plant roots into the soil. It would be best to choose plants that are adaptable to the specific area and the deep depths of water.

You can mark the layout using ground paint of wooden stakes. You can examine the layout and make changes according to your final plan. You should also mark the area where the water will flow. Once you’re happy with the layout, it is time to determine the garden size.

3. Choose a Garden Size

The next thing to consider is the size of the garden. How big should a rain garden be? Ideally, it would help if you planned on designing a garden at least 150 square feet so that you have sufficient space to include a wide variety of plants. After all, having a small rain garden is better than not having one at all.

Try to stand outside of the garden area as much as possible so that the ground under the garden is not packed down. Avoid placing any heavy machinery or instruments inside the area where you’re digging.

You can choose a small, round shape, such as a circle, teardrop, or oval. Make sure that you outline the specific area and shape with a rope if you’re starting from scratch and observe it from every angle to understand what the final result would look like.

You can determine the size of your garden by estimating the water that would run off the roof towards the spout at the time of average rainfall. You can do this by calculating the rough area of the roof that drains down the spout. A relatively smaller rain garden can still handle 75-80 percent of the water flow from storms and rainfall. Just make sure that the garden’s size fits well with the landscape.

4. Think about Garden Depth

You can figure out the depth of the garden based on how quickly the soil absorbs the water. The water should be able to drain within 24-hours after an average rainfall. You can even test the depth of the garden by digging a small hole in the area, filling it up with water, and waiting to see how quickly it absorbs in the soil.

You should maintain a depth of about 60 cm, leaving about 25 cm for water pooling, mulching, and planting. Don’t forget that rain gardens should be deep-set into the soil to allow water to filter and collect into the soil for absorption.

5. Choose the Soil

After determining the depth of the rain garden, it is time to choose the type of soil mix you’ll need. The type of soil you use can make a major difference in how well the rain garden functions. You will need a special soil mix that will contain a balance of sand and compost and is intended to allow water to flow quickly and easily.  

6. Create an Inlet

The next step is to create an inlet to allow the water to flow freely into the garden. The inlet also functions as the gateway for water to flow out of the garden in case of overfilling or flooding.

There are several ways to carry or direct water to the rain garden. It can be carried through the overflow pipe from your rain barrel or through an extension at the end of your downspout. You can also place a few stones around the area where the water will flow into the garden to protect the soil from being withered away.  

7.  Create an Overflow

The water that enters the rain garden will usually be soaked into the ground throughout the year. However, sometimes, the ground may get wet, fill up, and overflow when there is a big storm. Therefore, every rain garden should have a particular exit area to prevent the ground from overflowing. The overflow should be constructed towards the downhill side of the garden, allowing excess water to flow to an open area of the lawn or towards a second garden. You should also consider placing a few small stones around the overflow area (like you did with the inlet) to slow down the water flow and protect the soil from withering away.  

8. Select Plants and Trees

A good rain garden always has perennial plants. This is primarily because rain garden functions as a water storage area that helps perennial plants grow and nurture. Plants will be able to thrive in moist conditions as they will experience longer periods of wet soil. So it would be best if you chose plants that have average or moist water requirements. Some of the best plants for rain gardens include hardy geranium, black-eyed Susan, hardy hibiscus, coneflower, and false indigo. These plants should be placed in the deepest parts of the rain garden, whereas plants that don’t mind the occasional drought or require average-to-dry water flow should be positioned at the edge of the garden. Plants, such as catmint, butterfly weed, yarrow, coral belts, and gaura, are great choices.

You can add a small shrub or ornamental tree as a point of attraction, although a rain garden is not the best place to grow trees. Nonetheless, trees can significantly increase the water absorption ability of the rain garden. For instance, pawpaw trees, river birch, hackberry, or redbud trees would be great fits for a rain garden.

Maintenance and Care

Rain gardens typically require less care and maintenance compared to a flowerbed. You will have to provide additional care initially as the plants establish their root systems. To encourage healthy root growth, you must water deeply during drought.

Moreover, you must ensure there’s no weed growth in the garden to promote healthy plant growth and aesthetics. The best time to remove weeds is after rain. You can even try mulching to suppress weed growth. Fine, hardwood mulch is the best choice as it is less likely to drift away during the rain.

Tips and Techniques

• A rain garden should be considered a foundation planting or a border rather than a specimen tree. It should not be treated as a single aesthetic feature for the garden.
• You should design a rain garden at least 10 feet away from the house, but you should also consider other composition rules, such as circulation and screening.
• It would be best if you chose a shape that complements the existing design and features of the yard. Remember, your rain garden does not need a specific shape to function properly, so feel free to be creative.
• The main feature of a rain garden is the plants you choose. It can be as wild as you like or as formal – as long as it fits well with the overall design.
• You don’t have to keep the rain garden separate from the rest of the plants or trees. You can create a border with shrubs or a perennial bed, especially if you have compact space and don’t have much room.  
• You can also create a small rain garden for each downspout if it works well with the overall design. This way, you can have multiple rain gardens.
• Choose bright colored plants of varying heights to create variety and appeal.