The Garden Report: The value of a rain garden

Fri, 05/27/2016 - 1:45pm
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You may have heard the term, but what exactly is a rain garden? After a presentation by Lorraine Joubert of the University of Rhode Island Cooperative Extension Service on storm water runoff, my takeaway was that it is a glorified name for a ditch.

Storm water runoff was the subject of a joint meeting of the Planning Board and the Committee for the Great Salt Pond in April. Storm water runoff has been targeted as one of the greatest sources of pollution in our waters, and the presentation by Joubert was a first step in bringing awareness of the problem to Block Island residents. 

“Water seeks its own level,” is a quote I will attribute to no one, and it is more commonly a metaphor about life than about the actual flow of water. But in the case of storm water runoff, it all flows down hill, and usually that means into the nearest pond. Indeed, on Block Island, the water cascading down roads after a rain is quite often channeled into the Great Salt Pond by design. This water can come from surprisingly far away and it can carry all kinds of pollutants with it – lawn and garden chemicals, oil, salt, animal waste, soaps from cleaning cars and boats, and improperly dumped wash water. The excess nitrogen from fertilizers, in particular, can lead to algae blooms, which can then lead to the death of a pond. 

If you live on a hill and rainwater just washes down your drive and into the road, you are, however inadvertently, contributing to the problem. The purpose of a rain garden is to trap, or at least slow down, the flow so that the water may be absorbed into the earth, which at the same time filters it and recharges the aquifier.

Now, as I said, it can be as simple as digging a ditch, but you can get quite creative with it also, and there are lots of resources on the internet for both the technical and the artistic.  One concept is to create what is called a dry streambed. When it rains, you temporarily have what looks like a little stream that goes nowhere. 

One of the most useful looking sources of information is the web-site of the Rain Garden Alliance (www.raingardenalliance.org).  There they have instructions on basic “building” concepts, but more importantly, lists of plants that are most appropriate for the rain garden. These are plants, shrubs, and trees that can withstand both extremes of wet and dry. 

It turns out that the most popular plants for rain gardens are native ones, and that’s a win-win in many ways. Native plants are great — no, crucial — for wildlife, and they are often the easiest to grow because they are just right for the environment in which they reside. 

The biggest problem with adding native plants to your gardens is actually finding them for sale at local nurseries. At many, what one might think is a native plant is actually a cultivar.  While some do have a limited stock of native plants from Rhody Native, the best bet by far for finding a wide variety of native plants is at The Best Native Plant Sale in Rhode Island, brought to you by the Rhode Island Wild Plant Society. It only happens once per year — this year on Saturday, June 4, at the University of Rhode Island’s East Farm on route 108 in Kingston. (Hours: 9 a.m. to 1 p.m.) The Society does actually hold two sales per year, but the first, smaller one, specializing in “spring ephemerals” is past. 

The June sale is impressive, and advance press says that over 3,000 plants, trees, and shrubs will be available. I had the opportunity to go last year and, while not thinking about a rain garden, brought home many plants to try in my gardens, including lupines, butterfly weed, and a purple headed sneezeweed plant, which was much prettier than its name suggests. A black cherry tree, a native species that plays host to many types of insects set me back a mere ten dollars.

What was truly great about the sale was not only the variety, quality, and price of the plants, but the knowledge of the many volunteers manning the tables. Often they were the same ones who grew the plants, and so were intimate with the conditions in which their offerings thrive. 

Some of the plants suitable for rain gardens you will likely find at the June 4 sale are boneset and Joe-Pye weed, which is an important nectar source for monarch butterflies. I’m personally hoping to find some New York ironweed and white turtlehead, both native plants that seem to have disappeared from the island. And this year, I’m bringing a wagon. Hope to see you there!