In the growing struggle to curb stormwater pollution fouling urban streams and the Chesapeake Bay, one of the most promising tools could turn out to be the humble radish.
On a vacant lot in Northeast Baltimore, a researcher from the University of Maryland, Baltimore County is testing the potential of daikon or forage radishes to turn badly compacted city dirt into a natural sponge for rainwater.
Stuart S. Schwartz, a senior scientist with UMBC's Center for Urban Environmental Research and Education, hopes the experiment, dubbed B'more Rad, can find out whether cities could benefit from a plant that farmers in Maryland and elsewhere are increasingly raising as a cover crop to reduce polluted runoff from their fields.
With help from a local nonprofit and Baltimore City, Schwartz scattered a mixture of radish, clover and oat seeds this month on a tenth of an acre that until recently held rowhouses. He returned a couple of weeks later to find little round radish leaves poking through the straw laid over the bare ground after the seeding.
"See that little leaf in the center there?" he asked. "That's the first secondary leaf coming out. ... You can tell by the clumps here I went a little overboard."
Daikon radishes, a long, white variety of the red ones that often grace salads, can grow taproots as big as a person's arm. When farmers plant them after a late-summer harvest, their roots bore down through the soil, loosening it. Then, after winter frosts kill the plants, the roots decay, leaving behind deep openings that allow rain to soak in.
"It's very hard to measure runoff where you've planted the radish, because it all goes in the hole," said Ray R. Weil, a soil scientist at the University of Maryland, College Park who has been promoting the plant as a cover crop for a decade.
The radish not only loosens the ground, Weil said, it "fixes" or consumes nitrogen in the soil that might get washed off by rain or snow melt. The nutrients are then returned to the soil to fertilize the next crop as the radish plant dies and decays.
Schwartz said Weil's work with the radish on farmland inspired him to try it in an urban setting.
City and most suburban soil is badly in need of aeration, Schwartz said. He and other researchers have found that even grass-covered ground, just below the surface, is often as dense and impermeable as concrete. Anything heavier than a light rain runs off, washing fertilizer, organic matter and other pollutants into storm drains and nearby streams.
A few years ago, at Yorkwood Elementary School in Northeast Baltimore, Schwartz used another time-tested farm technique, subsoiling, to rip up playground soil that had previously been covered with asphalt. He showed there that treated soil absorbed water much more readily.
But such deep tilling of urban soils is labor-intensive, costly and difficult, with rocks and building rubble often lurking beneath the surface that can break the blades churning the soil.
The deep-rooted radish offers a relatively low-cost, low-tech way to break up urban soil, according to Schwartz, who spent only about $50 for the seed mix. The vacant lot on Perlman Place was provided through a partnership with the city and with Civic Works, a nonprofit that runs Real Food Farm nearby in Clifton Park. The lot is one the city is leasing to Civic Works for expanding its urban agriculture initiative.
"If they do it right, it ought to work," Weil said.
A volunteer with the group ran a Bobcat with a tiller attachment over the vacant lot before the planting, but Schwartz said the ground was so hard it only scratched the surface. The seeds got a layer of compost and straw to help retain moisture, and the city sprayed the lot once with a water truck to spur germination.
Kimberly Burgess, surface water management director for the city's Department of Public Works, said her agency is helping with the experiment because "we want to see creative, community-based programs that help Baltimore manage runoff and contribute to the greening of the city."
Baltimore's Office of Sustainability helped Schwartz find someplace to test the radishes because it fits with the city's Growing Green initiative, a broad effort to make neighborhoods greener, reduce stormwater runoff and make vacant lots less of an eyesore as the city works to promote eventual redevelopment.
"We're not sure what's going to happen, but we think it's worth trying," said Mark Cameron of the sustainability office. "We know things have to change, and it's better to start from the ground up.
If the experiment works, city officials are eager to try it elsewhere, Cameron said.
"We don't want lots that look like this," he added, pointing to an adjoining weed- and rubble-strewn field. "We want more green."
Schwartz said the radishes got in the ground on Perlman Place a bit too late to provide a good test of their soil-loosening ability. The best time for planting is in late summer, he said, but he wanted to find out what tilling of the ground might be needed to get the seeds to take root and grow. He said he hopes to do more plantings next year, including trying the radish on a state highway median, and to follow up by measuring runoff from the test plots.
Cameron said he's freelanced an experiment of his own, scattering some radish and grass seed mix Johnny Appleseed-style on another vacant lot that wasn't tilled at all. He also tossed some on a patch of his own backyard.
"I just wanted to see if it would grow," he said. Though it's a little spotty, he said, "I do have radishes coming up."