How to make a rain garden

"This is an opportunity to create something really elegant and pretty that also helps by capturing and filtering water."

In Dewey Square Park, across Atlantic Avenue from the Federal Reserve Bank of Boston, horticulturists have constructed a rain garden to collect stormwater that is absorbed by the plants, which act as natural filters.
A rain garden at Dewey Square Park in Boston, comprised of native plants of the Northeast. –The Boston Globe

If you want to help out the environment, you can plant a rain garden on your property.

Rain gardens collect rain water that flows from places such as your roof, driveway, and yard — collecting pollutants along the way — then filters the water so it doesn’t leave your yard, run into storm drains, and contaminate local waterways.

“It’s a garden with a purpose,” said Mark Chandler, director of research initiatives at Earthwatch, a nonprofit environmental organization in Boston, which will lead three free Rain Garden Training workshops at the Franklin Park Zoo in Boston on June 23, July 14, and Aug. 4. “It’s your small way of making a difference.”


Chandler offered four tips for making one.

1. Find the right place to put it.

You’ll want to place your garden where the water collects on your property, Chandler said.

How do you know where that is?

“You follow the water,” Chandler said.

During the next storm, pay attention to where water is flowing on your land and over impermeable surfaces such as your roof or driveway, Chandler said. As you’re figuring out where your garden will go, note that you’ll want to plant it at least 5 feet away from any buildings to avoid water damage, he said.

2. Decide the size of your garden and then dig.

The typical residential rain garden is between 50 and 100 square feet. You can figure out which size will work best on your property by using handy tools such as this sizing map, provided by the University of Connecticut, Chandler said.

Then it’s time to dig.

“Typically, you dig down 6 to 12 inches,” Chandler said. “You create this basin that will capture the storm water.”

Make sure your garden has a clear inlet, or location where runoff water enters the garden, Chandler said.

To keep the water from flowing into your garden too fast, you can put strategically placed rocks at the entrance, Chandler said. Or you can plant more bushes or thicker-stemmed plants there, he said.

3. Make sure your garden has the right soil and plants.


You need to choose your soil and plants carefully, so your rain garden functions the way it should, Chandler said.

“The plants will help absorb the nutrients and many pollutants,” Chandler said. “And the soil mix will also help filter the pollutants.”

You should choose permeable soil, Chandler said, which typically has increased amounts of sand.

As for the plants, Chandler said the following are good choices: New England aster, butterfly weed, iris, cardinal flower, bleeding heart, columbines, and hosta. You can also get more suggestions from your local gardening store.

“You need plants that are tolerant of having their roots submerged,” Chandler said. “They also should be tolerant of surviving periods of dryness.”

Choose plants you enjoy, he said.

“This is an opportunity to create something really elegant and pretty that also helps by capturing and filtering water,” he said.

4. Don’t forget to maintain it.

Periodically check to make sure the inlet to your garden is clear so the rain water can actually get in, Chandler said. You may have to clear away leaves, branches, and other debris.

Also, it’s a good idea to check that the plants are doing well and weeds have not taken over the space, he said.