Permeable paving: Good for the environment and your landscape
Less runoff, replenished groundwater levels, and tax savings are a few of the reasons why your home needs permeable paving.
Recently I traveled to Atlanta as a speaker for the Southeastern Flower Show. It was a beautiful and informative three-day show, with astonishing entries from both the Garden Club of America and the National Garden Club, competing in many categories. There were idea-gathering display gardens, fabulous photography and vendors offering everything from bulbs to complete designs.
However, among all this beauty, one of the most popular places at the show was along the back wall, an area dedicated to the mundane and practical aspects of water conservation. By the time I checked it out, much of the literature was gone — showgoers’ response had been unprecedented.
As well it should be. With the Southeast's recent history of prolonged drought, followed by inundations of rain and snow, water conservation has moved front and center for its gardeners.
Let the rain pour through
At my first stop, I learned about permeable paving and why we homeowners need it. Using a paving that water can soak through allows you to recharge groundwater on site, said masonry promotions manager Tom McCarty of the Georgia Masonry Institute. That means you don’t have to create extra swales, ditches, and/or piping to move the water away into storm drains.
Or you could gather the water from under the paving and move it to a storage tank. Depending on where you live — I know this is true in parts of my home state, Oregon — not having storm-drain discharge can also save you money in taxes.
Another bonus — the tiny holes in the porous paving conduct air up from the cooler earth underneath, thus lowering the temperature of the concrete on hot days. Cooler concrete around your house means the ambient air is not as hot, which, in turn, could make a difference in your air conditioning expense. And the plants along the edges of your paving, whether it’s a driveway or a garden path, won’t fry or need as much supplemental watering.
Tom was displaying two porous choices. The first was pervious concrete, a product that is laid down like regular concrete, except that the fine aggregate — usually an important part of a concrete recipe — is left out. The result is something that looks like pumice or a fine sponge, only much harder. It comes in colors and sets up like regular concrete.
The second product was permeable paving, a handsome grid of what appeared to be brick concrete pavers, widely linked together, with colorful gravel in between. This also allows water through—good for garden paths, as well as parking places.
Not easy being green
However, as with many developments that help the environment, there are certain challenges. In this case, installation costs are higher.
Part of that is because the installer must be trained to handle this concrete. For instance, the mix is much drier when laid down, and the usual techniques for finishing won’t work.
Also, the pervious concrete is inches thicker than its impermeable cousin — so that adds to the price. And it still doesn’t have the strength to bear the weight of multiton truck loads, although in home use, that shouldn’t be a problem.
In both cases, the preparation below the surface is more exacting, and often the substrate gravel bed goes down a foot or more, so that the water can be received into the soil effectively.
And what about plant growth on the medium? Tom told me that in Georgia, that’s not a problem.
But the Pacific Northwest where I live has been known for its "green" long before the term meant sustainability. And a lot of that color comes from moss. Would opportunistic moss spores clog the holes in the concrete?
According to Seattle installers Pervious Concrete, Inc. clogging of any porous surface can be a concern. However, even with my ordinary concrete driveway, I clean off the leaves and other detritus regularly and wash it down a couple of times a year. So if I took that kind of care with a permeable surface, there shouldn’t be a problem. And power washing goes a long way to keeping those tiny holes open and moss free.
In future postings I’ll talk about other water conservation methods I saw at the show, including the latest and greatest in graywater use, and why your next toilet should feature two handles.
Mary-Kate Mackey is one of eight garden writers who blog regularly at Diggin' It. She is co-author of “Sunset’s Secret Gardens — 153 Design Tips from the Pros” and contributor to the “Sunset Western Garden Book,” writes a monthly column for the Hartley Greenhouse webpage and numerous articles for Fine Gardening, Sunset, and other magazines. She teaches at the University of Oregon’s School of Journalism & Communication. She writes about water in the garden for Diggin’ It.
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