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Bogged Down?
1 Nov, 2008 By: Brian Albright LivescapesAlthough they can be a challenge, wet sites provide an opportunity for creative landscaping
Poorly drained, marshy areas can be a challenge for landscape professionals and homeowners alike. Excessive moisture can displace soil oxygen and suffocate the roots of many shrubs, trees and perennials, and even make it difficult to maintain many grasses.
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"You start getting root damage, and that invites fungal diseases," says Doris Taylor, plant information specialist at the Morton Arboretum in Lisle, IL. "The stress can also create insect problems."
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In many cases, homeowners want these areas filled in or drained, but with a little imagination and careful selection of native plants, these mini-swamps can be turned into attractive garden areas. Planting a large, water-friendly tree like a willow or cypress is an easy fix, but there are a wide variety of shrubs and herbaceous plants that thrive in wet sites and around natural water features like streams and ponds. "Bog gardens" have also become increasingly popular.
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"You can try to amend or modify a wet site to make it less challenging, but these sites provide opportunities to try different things than you could on the rest of the landscape," says Dennis Werner, professor of horticultural science at North Carolina State University in Raleigh. "Instead of fighting Mother Nature, you can take advantage of what the site offers."
To Drain or Not to Drain
If the client decides to use a wet site as-is, some drainage may still be necessary.
"Even for plants that tolerate wet soils, they may grow better if there is some drainage," says Leonard Perry, extension professor at the University of Vermont, Burlington. "If it's possible to improve the soil or add drainage using tiles or pipes, it should ultimately help growth."
In some cases, you can create swales or grassed waterways, or add a drainage line or dry well to divert the excess water. Raised beds are another option, depending on the design. Note that adding drainage tile, piping or a French drain could require special permits, depending on the location. There can also be special municipal restrictions on dry well placement and construction, and local utility companies would have to be called to mark any underground power or gas lines, depending on how deep you intend to dig.
"A swale is one of the least resource-intensive things you can do," Werner says. "If you can put in a swale, it saves you from going to the expense of raising the beds or installing a drainage tile."
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Before selecting plants for the site, it's a good idea to examine the soil and available light, and determine exactly just how wet the sites actually gets. If there is a significant amount of standing water for long periods of time, you might be limited to specific types of shrubs or pond plants. Other varieties can tolerate brief periods of standing water.
Wet areas are often low and draw cold air, which can damage certain perennials in the colder hardiness zones. Soil pH will also have an impact; azalea and winterberry, for instance, grow better in acid sites, while most trees prefer alkaline soils.
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