Rain Gardening in the South: a Review
The rain we've had this year is way above our 30-year average rainfall here in northern Florida. In April we received 5" (3.14" avg.); May brought 13" (3.48" avg.); and as of June 21st we've seen 11.3" (5.37" avg. for the whole month). We're not alone: much of the east coast has had more than normal rainfall.
In a year like this, rain gardens are more important than ever, which is why it's great to have a new resource: Rain Gardening in the South: Ecologically Designed Gardens for Drought, Deluge, and Everything in Between, by Helen Kraus and Anne Spafford. The authors are horticultural professors at North Carolina State University. Kraus has a Ph.D. in Horticultural Science, while Spafford is a landscape architect. Given their education, I was eager to read their take on rain gardens, even though I was pretty well informed on the topic. (I've written about our rain gardens and thoroughly researched the topic for my book, Sustainable Gardening for Florida that includes a chapter on rain gardens.)
This 146-page book is beautifully illustrated with color photos and diagrams throughout. The authors make an excellent case for rain gardens in their introduction:
"In the urban landscape, there's no such thing as a textbook water cycle. Instead, rainfall washes oil and other pollutants from roads and rooftops, and even sweeps up soil and fertilizers-mixing up a slurry of contaminated runoff. That highly polluted runoff them flows into municipal water collection systems. From there, it may go directly into streams and waterways... Soon, the lovely waterway-where you once dipped your toes or your children splashed-is green, slimy, and smelly... Quite a mess.
"Rain gardens to the rescue. They intercept polluted runoff, clean it, and return it to the water cycle... replenishing water reserves."
This book covers details of, soil science, garden design, and how to include rain gardens in a typical urban/suburban lot. I found the designing and location details informative and this portion of the book could be applied to any climate. The informal writing style is easy to read and I read the whole book in one sitting.
<< Two out of five design options provided for siting a rain garden (in red) into a sloped landscape. The diagrams in Rain Gardening in the South add greatly to its usefulness. Other diagrams show rain garden elevations, water flows, plant placement, how plants relate to existing landscape features, and more.
The authors include extensive plant lists for rain gardens: vines, groundcovers, shrubs, and perennials for shade, partial sun, and full sun locations. They added a short list of trees. The lists include cultivars, natives, and non-native plants. The lists are what makes the book for "The South," which the authors narrowly define as Virginia, The Carolinas, Georgia, and Alabama. I guess they do not include Florida as being part of "The South" because their plants include many temperate plants that could not survive in south Florida and one of the plants listed (Nandina domestica) is invasive in our state.
I thought their method for calculating the amount of water for sizing a rain garden was overly complex. I would have used a more simple formula: For every 1,000 square feet of impervious surface area, you receive approximately 600 gallons of water per inch of rain. While the authors included instructions for sizing rain gardens, they did not include much about drainage to handle extra heavy rainfall or if water doesn't soak in within three days. Perhaps they wished to keep their instructions simple, but I think they could have added more solutions such as embedded dry wells and/or French drains. They have a troubleshooting chapter in which they could have added more drainage options, but instead, they offered the option of reducing berm height if the rain garden is not absorbing the water in three days or less..
The authors did not cover how to test for drainage in your proposed rain garden site and even suggested that a persistent wet spot in your yard might be a good location for a rain garden. You can plant rain gardens plants in a wet spot, but the last thing it needs is more rainwater directed into it. I suggest that you site a rain garden "above" a persistent wet spot to soak up most of the rainwater most of the time and then only a small amount would be directed into the low spot where the water table intersects with the surface.
The authors included a throwaway chapter on "other" water-wise landscaping methods, including using rain barrels, drip irrigation, and porous pavement. The rain barrels were treated with distain as "not being terribly attractive" and that when it's rainy you'll never use all that water. It seems as if the authors considered rain barrels as alternatives to rain gardens when, in fact, rain barrels can overflow into rain gardens, leaving the stored rain water to use for outdoor irrigation. Water is an important resource and collecting rainfall reduces the strain on our water systems.
Even with my quibbles, I still think Rain Gardening in the South is a worthwhile book for its design aspects-sufficient details for the beginning rain gardener to get started and enough principles of design and water flow analysis with the landscape for the more advanced gardener. Rain gardens play an important role in stormwater management and water pollution reduction. We need more rain gardens in The South, where frog-choking gully washers can happen at any time, to improve overall water quality of our rivers, lakes, and aquifers.
Buy the book and build your own rain gardens. Then the next time we have too much rain, you'll be ready to absorb all of your stormwater.
Ginny Stibolt would like to hear from readers who have suggestions and questions. After all, there are more than a few transplanted gardeners here in northeast Florida trying to figure out what works and what doesn't in planting zone 8/9. She's written a book, "Sustainable Gardening for Florida," to be published by University Press of Florida in September 2009.