A study by the American Society of Landscape Architects found that over 71% of its members expect to see rain gardens become increasingly popular this year. Rain gardens and their siblings, bioswales, can help landscape professionals address drainage and runoff on their customers’ properties without sacrificing the visual appeal of the area.
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“It’s a way to manage stormwater, especially creating an aesthetic way to do that,” James Hartsig, a certified professional soil scientist with Keenesburg-based Duraroot Environmental Consulting, said.
For Cheri Stringer, owner and founder of TLC Gardens in Longmont, rain gardens and bioswales are part of a larger movement to integrate beautiful design with efforts to reduce the amount of chemicals and sediment in water runoff.
“It’s not just flowers. It’s creating a framework of view corridors and pathways, while at the same time creating something that can contain water on the site, filter it and provide a biohabitat,” she explained.
Iana Iavorskaia, a designer at TLC Gardens, noted that some studies have found that as much as 70% of pollution comes from stormwater runoff and estimates suggest about 30% can be handled by rain gardens and bioswales.
Iavorskaia said that sometimes rain gardens and bioswales are treated as an afterthought and called on designers to integrate them into larger landscape designs.
“As designers, we really can incorporate them” into any space, she said. “They don’t have to be round; they can be square. We can make it look contemporary, modern, natural. We can frame it with trees and shrubs instead of having a random bed of perennials, or create a dry creek that leads to it.”
Choosing a site
One of the first steps in designing and installing these types of projects is educating clients on the difference between bioswales and rain gardens and identifying which is appropriate for the client, according to Stringer.
The main difference, she said, is engineering. “Bioswales are engineered soils, they’re engineered slopes. They’re engineered to hold a certain amount of water and a certain flow of water.”
For example, municipalities may be interested in creating a bioswale near a parking lot to filter chemicals and sediment from water running off the pavement.
Once the decision is made to install a rain garden, landscapers and designers need to assess the property for the best location. If there aren’t low areas for water to naturally collect, some digging or grading may be necessary. Although low areas are ideal sites for a rain garden, guidance from the Colorado Stormwater Center at Colorado State University notes that the garden itself should be as level as possible.
“Once you’ve identified that area, you want to make sure that you have the right design capacity to hold however much water is feeding that system. That can be a quick calculation based on the size of the property,” Duraroot’s Hartsig explained.
According to the Colorado Stormwater Center, the surface area of a rain garden is based on the size of the customer’s roof, the depth of the garden, expected runoff and, of course, the available space in the area.
The goal is to create an area that can infiltrate an inch of water every hour. In Colorado, where landscapers will frequently encounter clay soils, that means they’ll have to mix course, sandy loam into the garden area. Hartsig recommends using that type of soil for between 65% and 80% of the soil matrix and using a compost that can aid in infiltration for the remaining 20% to 35%.
“One of the really cool things about rain gardens is you’re creating an area that can handle the capacity and then getting that stormwater or rainwater back into the soil, back into, hopefully, that groundwater system,” he said.
What to plant
Although many people use “rain garden” and “bioswale” interchangeably, TLC Gardens’ Stringer said there are some differences. Rain gardens may be more creative and less engineered, she noted.
“One of the most inspiring rain gardens that I’ve ever experienced was done as a pathway through a side yard,” she said. “The rain garden was set up to look like a pond. It had plant material at different stages that allowed the water that was coming off the runoff to flow at different speeds and hold different levels of water.”
Plant options are extensive and can include flowers, trees, shrubs, grasses, perennials and ground cover. Some popular designs among her clients include rain gardens that resemble streams with bridges across them.
“A lot of clients want lower maintenance” gardens, Iavorskaia added. “In Colorado specifically, people are very environment-conscious. Using native plants definitely answers those demands.”
Rocky Mountain maples, which can handle sitting in water, are a good choice, as well as sand dropseed and golden columbine.
“They know how to handle Colorado,” Iavorskaia said. “They’re fine with the drought and they can tolerate some standing water for a short period of time.”
“Your backyard can become part of the ecosystem and that’s very satisfying to know that it works like it should.”