When you read nursery catalogs or the plant labels at your local garden center, it's easy to get the impression that all plants 'need good drainage'. You never see a description for a plant that says 'needs poor drainage' or 'likes swampy soil'. Yet most gardeners have experienced areas of wet mucky soil in their yards. Garden books list plants for sun, shade, regular irrigation, drought tolerance — why not bad drainage?
The answer is that no plant truly requires poorly drained soil. But many will tolerate boggy conditions, even thrive in them. Plant labels will list these as having high water needs, but how do you know what needs a lot of water and good drainage, versus those that will grow happily in that obstinate area of saturated clay in your backyard?
Rhododendrons require lots and lots of water, but need perfect drainage. They're from moist temperate climates, especially mountainous places with high rainfall and rich forest soil that holds water like a sponge. They would be a terrible choice for a swampy part of the yard. Instead, look to species that actually grow in swamps. You might even consider accentuating the swampiness in places by excavating broad shallow basins to create little wetlands. After planting, fill the basins with mulch or decorative gravel so there is never actually standing water on the surface.
IN LARGE WET AREAS there are a few plants that will spread a long way, making it cost effective to create a beautiful landscaped marsh:
has large strap-like leaves reminiscent of an iris and can be mowed with a brush mower to keep it in check; several dwarf ornamental varieties with colored foliage are available
has hollow stems and a stiff, erect growth habit; its deep green color mixes well with lighter foliage like sweet flag
is a spreading groundcover with triple variegated green, cream and pink foliage and loves to grow in permanently wet soil; it is shorter than sweet flag and horsetail, making a nice accompaniment to these upright growers
IN SMALL SWAMP GARDENS the preceding species will quickly take over the space, though they are still useful if planted in submerged pots to contain their rhizomes (roots). However, here are a few options for smaller spaces that will create a big visual impact:
(Hibiscus moscheutos, H. palustris)
has dinner plate size blossoms on head high stalks and possesses the charm and good looks of other hibiscus species in a form that will grow in boggy soil
has 12-inch spikes of brilliant red flowers that hummingbirds adore; it is a short-lived perennial, but will usually seed itself
grows from tuberous roots, putting out tropical-looking blossoms from the top of stout 4-foot stalks; varieties with colored foliage are also available