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Ask the Expert: Jeff Lorenz on Planting Strategically for Stormwater Management

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Ask the Expert: Jeff Lorenz on Planting Strategically for Stormwater Management

November 15, 2023

As rain events have become more intense and more frequent, you may have noticed stormwater from the street flooding your property, rainwater from downspouts carving gulleys into your yard, or a wet patch that never seems to dry out. All of these issues can be addressed with plants.

Jeff Lorenz, the founder of Refugia Design in Philadelphia, is known for designing immersive, native landscapes, but he’s also developed something of a knack for creating gardens that effectively manage stormwater. Refugia’s style is naturally well-suited to the task: The native plants that they work with are good at Lorenz’s three rules of stormwater management: 

  1. Slow down stormwater, allowing the ground to absorb the initial surge. 
  2. Spread the flow of water across the surface.
  3. Soak water back into the aquifer with the help of deep-rooted vegetation.
Refugia&#8\2\17;s garden for the Bryn Mawr Film Institute manages runoff from the roof and neighboring parking lot through a mix of diverse flowering perennials and grasses with a variety of root depths.
Above: Refugia’s garden for the Bryn Mawr Film Institute manages runoff from the roof and neighboring parking lot through a mix of diverse flowering perennials and grasses with a variety of root depths.

Plus, planting densely, as Refugia does, is a stormwater management trick in its own right. “Rain gardens seem complicated, and sometimes they are for good reason, especially in larger applications, but for most residential settings, just creating larger, more vegetated planning beds has a great impact on stormwater issues,” says Lorenz. 

Below, he offers tips on how to have leverage your garden to help with stormwater management.

Photography by Kayla Fell, courtesy of Refugia Design.

Reduce your lawn and increase your beds.

The site at Bryn Mawr Film Institute before Refugia&#8\2\17;s landscape redesign. The first order of business was to reduce the “green concrete” of lawn and replace it with resilient plants with a variety of root structures.
Above: The site at Bryn Mawr Film Institute before Refugia’s landscape redesign. The first order of business was to reduce the “green concrete” of lawn and replace it with resilient plants with a variety of root structures.

“Reducing your lawn has a massive impact on stormwater,” says Lorenz. “We call it green concrete because it has very little absorption quality.” Consider expanding garden beds. Fall is a great time to plan for this, as you can pile up leaves on the part of the lawn you plan to turn into new beds come spring (see Why (and How to) Leave the Leaves). Two places Lorenze says you should definitely consider expanding your beds are where downspouts flow out, and anywhere your border beds are close to a low, wet point in the lawn. “Bring your garden bed out to incorporate that low point.” 

Rethink how your care for your lawn.

Above: Refugia dramatically reduced the amount of lawn in this front yard, replacing it with plants that will help to soak rainwater back into the ground while simultaneously increasing biodiversity in the landscape.

For the lawn you do keep, consider tweaking your care routine. Let the grass grow higher and mow less often. “If you have a thicker, taller vegetation above ground, that’s going to help slow stormwater down,” says Lorenz. When it’s time to reseed, consider reseeding with fine fescues (and gradually transitioning the whole lawn), or if you’re open to a bigger change, replacing the turf with a full fescue or sedge lawn. Lorenze notes that in trials at the Mt. Cuba Center wood’s sedge (Carex woodii) was the best performing sedge lawn alternative for the Mid-Atlantic that can tolerate moderate traffic. (For more on this grass-like perennial, see Trend Alert: A Carex for Every Garden.)

Irrigate less.

Your irrigation might also need some rejiggering. “We discover a lot of properties that are always at a point of saturation because they’ve got these robust sprinkler systems that are keeping the ground wet,” says Lorenz. The ground loses its ability to absorb water in an actual storm, if it’s already saturated, but if it has the chance to dry out a bit and it has more absorbing capability. Dialing back your watering schedule will also have a positive impact by reducing the water your yard consumes. The ultimate goal is not to irrigate at all, says Lorenz, “We aim to make irrigation systems redundant, by using plants resilient in your area, that don’t require long-term coddling.”

Seek out native, resilient plants.

Lorenz’s own home demonstrates many of the principles of stormwater management, including dense plantings, a sedge lawn instead of turf, and a variety of root structures—not to mention permeable pathways.
Above: Lorenz’s own home demonstrates many of the principles of stormwater management, including dense plantings, a sedge lawn instead of turf, and a variety of root structures—not to mention permeable pathways.

Putting plants in the path of stormwater or the place where the water gathers is key, but make sure they can handle both wet and dry periods. “You’ll water them the same as you would any other planting bed you’re trying to establish, but then the idea is that the plants can handle periods of dryness—even drought—and being kind of flooded,” says Lorenz, who notes that many grasses fit the bill. The best plants are going to be plants indigenous to your particular region, and a native plant nursery will be able to help you identify what will work best in your environment.

If you’re looking for plants to soak up rain in shadier areas, Lorenz suggests asking your nursery about different sedges (carexes) that will thrive in your area. “Carexes might not produce a root system quite as deep as switchgrass, but they will help slow water down and soak it up,” he says; for example, Pennsylvania sedge (Carex stricta, pensylvanica) and fox sedge (Carex vulpinoidea) produce root systems from 12 to 24-inches deep. Also consider adding to your shrub and understory layer. In the mid-Atlantic where Lorenz works, he uses white meadow sweet (Spirea alba), native smooth hydrangea (Hydrangea arborescens), and viburnums as well as small understory trees like dogwoods, including red twig dogwood or silky dogwood, and witch hazel.

Beef up your plantings.

For the Bryn Mawr Film Institute garden, Refugia Design replaced turf grass with a filter strip and basin to one side of the pathway that reduces runoff from the adjacent parking lot. As a bonus: the more robust plantings are a more immersive experience for visitors.
Above: For the Bryn Mawr Film Institute garden, Refugia Design replaced turf grass with a filter strip and basin to one side of the pathway that reduces runoff from the adjacent parking lot. As a bonus: the more robust plantings are a more immersive experience for visitors.

“Densely-planted foundation and border plantings are a great way to start slowing water down,” says Lorez. This is especially true if you have a lot of water coming off your roof and the downspouts pass through your beds. Tip: If you have water getting in your basement, make sure that the beds around the house are pitching away from the house one or two degrees. 

Companion plant for better water absorption.

“One of the key things that we look at is a diversity of root systems,” says Lorenz. In a forest, you’d find deep tree roots and lots of plants with surface roots in the herbaceous understory. As an example of a simple combination, Lorenz points to irises, which are great at slowing water down, paired with switchgrass, whose deep root system helps create a pathway for water to go back down towards the aquifer. One note: Do not plant deep-rooted plants near dry wells or septic systems.

Add this stormwater superstar.

Refugia uses switchgrass, like Panicum virgatum &#8\2\16;Shenandoah&#8\2\17; seen here in the foreground, in its rain gardens because its dense clumps slow water down and its vigorous root system helps water soak back into the ground.
Above: Refugia uses switchgrass, like Panicum virgatum ‘Shenandoah’ seen here in the foreground, in its rain gardens because its dense clumps slow water down and its vigorous root system helps water soak back into the ground.

One plant appears in almost all of Refugia’s rain gardens and mini bioswales: Switchgrass (Panicum virgatum). This perennial grass is native in much of the United States and Canada. Its root systems can be three times the size of the aboveground plant, and not only can it help water soak in, it can help filter petroleum-based pollutants out of the water if you plant it where it will catch un-off from your driveway or the street.

Reclaim your soggy spots.

A mix of medium and large stones positioned near a downspout prevent soil erosion and mimic the look of a natural stream.
Above: A mix of medium and large stones positioned near a downspout prevent soil erosion and mimic the look of a natural stream.

If you’ve got a spot on your lawn that collects water every time it rains, you can use that area to your advantage and make a mini rain garden. “You might even want to articulate the grading a little, dig it out a bit more, and then vegetate it,” says Lorenz. Plants in the center of the rain garden need to be able to be happy with wet feet for a few days and also okay with periods of dry. Plants that fit the bill include many grasses, Joe Pye weeds (Eupatorium spp.), and irises like blue flag and dwarf crested iris (Iris cristata). Use the dirt you’ve excavated to create a gentle berm around the perimeter to help direct the water where you want it to go and avoid overflow in the depression. “We usually just use the excess soil and some stone from the dig, and then plant them so that they have root stabilization,” says Lorenz.

Work with the flow.

Water finds the path of least resistance, and you can often see evidence of where it naturally wants to flow. If you have a place where a gully has formed, Lorenz suggests creatively putting some stones and plants into the path of where the water flows; this could be a decorative arrangement of small and medium-sized stones right at the end of a downspout or boulder-sized rocks and shrubs in the path of an overflowing street drain. “In the mountains or forests you’ll see an ephemeral stream where you can tell that water flows from time to time, but it is dried out,” says Lorenz. “You’re just making a little naturalistic feature out of it.” Tip: If water flows so intensely that you’re afraid your new plants will be swept away, Lorenz says you can use sod pins or stakes to help them get established.

Filter the road water.

 This garden features a bioswale that was exacavated from the lawn to create a depression to hold rainwater and act as a filter strip to the road.
Above:  This garden features a bioswale that was exacavated from the lawn to create a depression to hold rainwater and act as a filter strip to the road.

If water flows off the street or your driveway, you might consider planting a “filter strip,” which is planted along the sloped areas commonly found alongside roads, or even a mini bioswale, which is intentionally dug out to hold and direct water. “They’re meant to catch an initial stormwater rush and hold it to soak back into the ground or guide it somewhere where there’s maybe a larger catchment point,” says Lorenz. The vegetation can even have the capability to pull toxins out of that stormwater before soaking back in. 

Engage your neighbor.

As you make changes on your property, share your efforts with your neighbors, especially anyone who is in the same path of stormwater. “As these superstorms keep coming in, you’re not going to have a perfect answer,” but the best solution is when a whole neighborhood works together, he says. “When it’s not just one property but multiple properties, that’s when you start to make an impact.”

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Frequently asked questions

What is stormwater management?

Stormwater management refers to the management of rainwater runoff from impervious surfaces, such as rooftops, roads, and parking lots, to minimize flooding and water pollution.

Why is stormwater management important?

Effective stormwater management is important to prevent flooding, reduce erosion, protect water quality, and recharge groundwater supplies.

How can strategic planting help in stormwater management?

Strategic planting involves using vegetation to capture and slow down rainwater runoff, allowing it to infiltrate the soil. This helps reduce the volume and speed of runoff, preventing flooding and allowing water to replenish underground aquifers.

What are some examples of strategic planting techniques?

Examples of strategic planting techniques include creating rain gardens, installing bioswales, planting trees and shrubs, and using groundcover plants to absorb rainwater.

What is a rain garden?

A rain garden is a planted depression in the ground designed to capture and absorb rainwater. It is usually planted with native plants that can tolerate both wet and dry conditions.

What is a bioswale?

A bioswale is a vegetated channel or depression that helps absorb and filter stormwater runoff. It is often planted with grasses, sedges, and other wetland plants.

How do trees and shrubs help in stormwater management?

Trees and shrubs have deep root systems that can absorb and store large amounts of water, reducing runoff and providing groundwater recharge. They also help to stabilize soil, preventing erosion.

What are the benefits of using groundcover plants in stormwater management?

Groundcover plants, such as low-growing grasses and spreading plants, can help absorb rainwater and prevent soil erosion. They also provide additional filtration and can enhance the aesthetics of a landscape.

Are there any specific plants that are recommended for stormwater management?

Yes, certain plants are more suitable for stormwater management due to their ability to tolerate wet conditions and absorb large amounts of water. Native grasses, sedges, ferns, and wetland plants are often recommended.

How can homeowners incorporate stormwater management techniques in their own gardens?

Homeowners can incorporate stormwater management techniques by creating rain gardens, planting trees and shrubs, using permeable paving materials, and directing downspouts to vegetated areas. Consulting with a landscape design professional can also be helpful.

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