Rain gardens are a great way to use natural irrigation and native plants to build a bountiful garden. After a heavy rain, that water should normally absorb back into the ground. However, with more impervious surfaces like roofs and roads, that rain has less land to soak into. This leads to flowing runoff that collects pollutants and toxins as it flows into waterways.
Rain gardens work on just about any property. Through a combination of soil composition, native plants, and natural filtration, rain gardens can help eliminate runoff and the pollutants it contains.
Here are 7 steps to build a rain garden on your property.
1. Select the Best Location
For the garden to be effective, the proper location is essential. Your rain garden should sit where it receives the most runoff. This is usually by the downspout of a house, or on a slope. The location should also receive sun and shade to facilitate the natural cycle of water.
If the majority of your runoff comes from the roof, then situate the garden within 30 feet of the downspout. However, make sure to keep the garden at least 10 feet from the house. If it’s placed any closer, the water-saturated ground could disrupt the foundation.
Slopes, ditches, and natural flow ways also make ideal locations for rain gardens. When digging, call the proper authorities to check for buried power lines. If your property is large enough, consider multiple rain gardens wherever needed.
2. Know Your Soil Type
Your rain garden will thrive no matter your soil type, but some soils are better than others regarding drainage and filtering.
Sand and sandy soils have high absorption, making sand an excellent base for a rain garden. On the other hand, heavy-clay soils are slow to drain. Remedy this by mixing sand or topsoil to the dig site. Typical soil compositions include:
- Loamy Sand: A fast-draining composition, this features at least 80% sand, with the remaining amount split between clay and silt.
- Silt Loam: Add silty soil to heavy-clay soil to achieve a ratio of 75% silt to 25% clay.
- Sandy Clay Loam: A balanced mixture of 60% sand, 30% silt soil, and 10% clay.
All of these mixtures work great in a rain garden. Different soil compositions work better with certain native plants. Research what the plants need, and incorporate that knowledge into your garden for the best results.
3. Plan the Rain Garden’s Size
The ideal rain garden size ranges between 100 and 300 square feet. High-clay soils need more area to improve absorption through the thick soil. Sandy soils better support small-scale, more efficient gardens in smaller footprints.
To determine the best size, grab a calculator and do some math. If most of your runoff comes from the roof or a driveway, multiply the length and width of the surface to find its area. Then, multiply that area by how much runoff you hope to drain. Typically, this is around 5%. Your final figure is the needed square feet of your rain garden.
Next, you need to determine the slope of your digging area. Follow these steps to find the pitch:
- Place stakes at the highest and lowest points of the slope. Run a string between them, ensuring the string is level despite the elevation difference.
- Measure the distance between the stakes, and the height of the string at the downward slope.
- To find the slope number, divide the string height by the distance between the stakes. Then, multiply by 100 to convert it into a percentage.
Gardens on slopes of 4% or less need a depth of 3 to 5 inches. On slopes greater than 4%, dig 6 to 8 inches deep. These depths slow and collect the runoff within the garden based on the slope.
With the size in hand, it’s time to start the prep work.
4. Best Tools and Supplies for Rain Gardens
Creating a rain garden is a bit more involved than digging a hole—but not much! To begin, gather your needed landscaping materials. These include:
- Topsoil with any needed amendments, including straw, mulch, and sand.
- Native flowers, grasses, and trees.
- Filtration stones, such as 1½ inch gravel and crushed stone smaller than 1 inch.
Choosing your plants is one of the most important steps. They form the basis of the garden, and their roots create the filtration and erosion control needed to fight runoff.
Using native plants is best for several reasons. They are already adapted to the natural conditions and pests of the area. They also provide habitats for local insects and animals, including honey bees. Native plants are additionally guaranteed to be in your hardiness zone. As well, consider drought resistance, root size, and absorption qualities.
Using native plants ensures your rain garden benefits the environment in several ways.
To aid the plants, add new topsoil to the dig area. This creates the proper grading to allow water to collect in the garden. Likewise, the stones act as filtering substrates. This allows solids and other pollutants to stay behind as the water flows back to nature.
As far as tools, keep it simple. You’ll need shovels and rakes to dig. You’ll also need string and stakes to mark out your area, and a level and tape measure to ensure proper grading. With these supplies in hand, you’re ready to dig!
5. How to Dig Your Rain Garden
Once you find and measure the ideal location, it’s time to dig.
Soak the area and wait overnight before digging. This will aid the process. With a shovel, dig out the center and create a berm around the garden. It is higher at the bottom in order to keep the runoff within the garden. Creating a compact ledge of 8 inches at the downslope edge is essential for the garden to function.
Next, cover the berm with mulch or stones to prevent erosion. Use the soil from the dug-out area to ensure the berm wraps around the garden. Once complete, fill the garden hole with topsoil and other mixtures to achieve the ideal ground compositions.
At this point, the garden is ready for planting
6. Plant Your Rain Garden!
Planting the rain garden requires a little planning. To start, consider how much rain flows through the area. Will the rain garden see constant use, or just a few times a year? If the latter, begin with drought-resistant plants at the center low point of the garden. These often have the highest absorption rate, which is perfect for heavy runoffs. If you receive plenty of rain, look for wetland-based plants native to the area.
The edge of the garden should contain plants with lower absorption rates. These will help protect the center plants. As well, their roots will help prevent erosion and create an absorbing soil network.
Trees and shrubs go around the outside of the garden. Often, these are for decoration, but they are also helpful beyond aesthetics. And speaking of decorative, finish the garden with paver stones or other landscaping rocks to improve curb appeal and prevent erosion.
7. Maintain Your Garden
Another benefit of native plants is their low maintenance. With some simple care, a rain garden becomes self-sustaining in a matter of years.
Water the garden every week for the first year like any other garden. Shoot for an inch of water each week to establish a robust root system. After a couple of years, the garden will thrive on natural rainfall alone. If you collect rainwater to irrigate your other gardens, do the same for the rain garden.
Some pruning is necessary to keep overgrowth in check. Weed the garden for the first few years to ensure your plants have no competition. Mulch helps keep weeds at bay. Eventually, the weeds decrease as the plants grow.
In areas with cold winters, protect the garden by pruning back plants. Cover the soil with mulch or compost to keep it warm. An established rain garden works even under heavy snow. So, keep the garden in shape for year-round functioning.
Rain gardens are simple tools that anyone can dig. They help reduce pollution and control the dangers of stormwater runoff. A rain garden full of native plants soon becomes a thriving ecosystem for local plants, animals, and insects. They also add great curb appeal to any property.
If you want to help your neighborhood, then consider a rain garden to detoxify the land around you.