How-To: Building a Rain Garden

If you live near a storm drain or have a yard prone to dampness, you might dread even light rainstorms. The resulting standing water and muddy mess can be a major frustration. However, our latest Eco Action can fix your standing water problem and help better your local watershed.

Rain gardens are an excellent way to integrate ecofriendly practices into your home. They’re designed to absorb water quickly, slowing down the flow of runoff and lightening the load for storm drains. The garden’s design allows the draining water to filter through plants and soil, cleaning the water as it trickles its way down to the water table. Size doesn’t matter – rain gardens come in all shapes and sizes. Rain gardens are also a great opportunity to provide homes for native plants and for the pollinators that love them, too.

Time Needed

This project will require 2–3 hours of pre-planning. The actual garden setup should take about half a day.

Before You Start

• Choose a good spot in your yard for your rain garden. Where are your downspouts located? When it rains, observe the way water flows through your yard. Does it all seem to drain in one direction? That’s where your garden should go. Rain gardens are best located on level ground, but as long as your slope is less than 12°, your rain garden should be ok.
  • Try to place your rain garden at least 10’ from your home. Any closer, and you might harm your foundation. The same applies to septic tanks.
  • As you would with any digging project, call 811 before you start. This free service will map your utility lines and help you figure out where your lines are. Allow a few business days for this service to be performed.
• Choose the right shape for your garden. While some folks can have square or narrow rain garden beds, most tend to favor rounded, more naturalistic shapes like ovals, teardrops or kidneys.
• Pick your plants. The Home Depot has a few suggestions here, but in general, the plants you choose should be able to thrive in both damp and drought conditions. Your plant hardiness zone and local ecosystem will help determine which plants will be most successful. The Wildflower Center has a great list of native plants by state, but you can also contact your local watershed authority or gardening club for recommendations. It’s best if you plant a mix of plants to give a variety of water absorption. Shrubs, grasses, perennials – you have plenty of options!
• Calculate your roof area. This will help you determine how large and how deep your rain garden will be. This handy calculator from the Rain Garden Alliance will get you the right measurements. It will also account for your soil type and yard slope and tell you how many gallons of rainfall your new garden will capture.

Let’s Get Started

1. Using your area calculations, outline your shape with stones or spray paint.
2. Time to start digging. You can use your shovels to get started, but if you want to save time, consider renting a sod cutter to speed things along. Use some of the displaced soil to create a short, earthen wall, or berm, at the far end of your garden.
3. Use your ruler to make sure that your dugout is the correct depth. If your garden is too deep, standing water can build up and create a mosquito hotspot. If it’s not deep enough, water may wash away before it has time to absorb.
4. The edges of your rain garden should all be level to better contain runoff. To ensure this, use your level and string to measure across from end to end. If you come up a little short, use some of your leftover dirt to shore it up and make it level.
5. Once you’ve gotten your garden to the correct depth, use your river rocks to create a swale, or water pathway, leading from your downspouts to the new garden. The rocks should be large and heavy enough to withstand drainage from the heaviest rainstorm and prevent soil erosion.
6. Fill your garden with soil. Ideally, your soil should contain sandy soil, topsoil, and compost to provide good drainage and a nutritious bed for your plants. Speaking of…
7. It’s time to plant! Seeds and seedlings might get washed away by runoff, so it’s best to plant more mature specimens that will establish deep root structures more quickly.
8. Once you’ve planted, lay down about 2–3” of heavy mulch to further anchor your plants. Lighter mulches will wash away, so choose denser options like shredded wood or pine straw.

Aftercare

While your rain garden is settling in, continue to water and weed. As your garden matures, it will need less watering and maintenance overall, depending on your plant selections.

You’re all done. Enjoy the benefits of your rain garden for years to come – your watershed, pollinators and local ecosystem will thank you.

Sources

• How to Build a Rain Garden, This Old House
• Ditch the Barrel: Here’s How to Build a Thriving Rain Garden this Season, Realtor.com
• How to Build a Rain Garden in Your Yard, Family Handyman
• Rain Gardens 101, Anoka Water Conservation District