Places to grow

To build her rain garden, Dale dug a one-by-five metre hole in the sandy soil of her front yard and lined the depression with a perforated pool liner. She created a basin of stones at one end, refilled the hole with soil and planted native wetland plants. Then she rerouted the downspout from her eavestrough so that water flows into stones, where the erosive force of falling water is absorbed, and then flows into the soil. “I’ve only seen it overflow once in a heavy rainstorm,” says Dale. “And in the most prolonged periods of drought, only the tips of some of the plants have become a bit crispy.”

These landscaped depressions act as sinks, collecting and retaining rainwater runoff from rooftops, paved areas and compacted soils. Rather than pooling in the bog, the water seeps into the earth, so mosquitoes are not a problem. And while rain gardens are exotic in comparison to traditional city gardens or lawns, they have a wild beauty, filled with native flora such as swamp rose, milkweeds and irises.

Homeowners can achieve some of these benefits without building an entire rain garden simply by redirecting downspouts so that they pour water over lawns and gardens rather into streets and storm sewers. “There’s really no reason to have water disappearing from your property,” says Dale. “Once you’ve done the work of digging, a bog garden is pretty much maintenance free.”

Some newer subdivision projects are even building neighbourhood-scale rain gardens to capture runoff while also injecting biological diversity into the monoculture of lawns. Called bio-retention zones, they siphon runoff from blacktops and compacted soils to reduce or even eliminate the need for storm sewers and drains. “Stormwater retention ponds are the most positive environmental improvements coming out of new subdivisions,” says Lamb. “They retain runoff and provide habitat for desirable wildlife like butterflies, red-winged blackbirds, small mammals, toads and dragonflies.”

Large engineered rain gardens perform another useful function, absorbing and breaking down waterborne impurities. The bog traps fertilizers, pesticides and organic wastes, as well as petroleum-based pollutants such as gasoline and motor oil. Held in the soil, they evaporate or become less harmful, says Harder.

Some bio-retention zones can be placed alongside parking lots and industrial lands to draw heavy metals from contaminated industrial runoff. The metals lock onto organic soil particles in chemical bonds, Branfireun explains, so that the metals are retained. A Maryland study revealed that rain gardens can capture up to 95 percent of lead from contaminated runoff. Branfireun’s research shows that these natural areas also retain the majority of atmospheric mercury fallout, for years or decades. “Heavy metals and toxins become an issue when trace levels are routed directly to surface waters where bioaccumulation occurs in the food chain,” says Branfireun. “Once these things are contained within the soil, migration is less likely.”
Many U.S. communities have created incentive programs for homeowners to build rain gardens and instructional packages about how to do so. Canadian cities have been slow to follow. Branfireun says rain gardens, rain barrels and high-rises with green roofs will become increasingly important if climate change brings about more extreme storms. “Our cities are not engineered for the types of events that we’re likely to see,” says Branfireun. “There really should be massive incentives to do these types of things.”

Part of the trick to making rain gardens more popular, says Dale, is helping people understand the ecosystem benefits of natural landscaping and native vegetation.

She applauds the City of Toronto’s ban on cosmetic pesticides last year, which Ontario followed with a province-wide ban. And she raves about the natural landscaping at High Park. “We need to make [rain] gardens more visible on the front lawns of residential streets so people can see how easy they are to maintain and how well they work.”

Dale downplays the flattening of her own rain garden. Much of the vegetation grew back and she had her bog functioning a year later. As for spreading the good news about her garden, she says children in her neighbourhood have bought in to the idea. “If only we could get their parents to follow.”

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Freelance writer and frequent ON Nature contributor Conor Mihell does not own a lawnmower. He reports on environmental issues from his home in northern Ontario.

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