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Did you ever stop to think how much water rolls off your roof each year? If you live in Tucson, the quantity might be small. But in Northern Virginia where I live, summer thunderstorms and winter snows drop 40 inches of precipitation annually.
Some minor calculations indicated that just half of my roof could supply me with 14,000 gallons of water a year. Instead of drowning my lawn, I reasoned that quantity could fill a big fish tank or moisten a nifty little marsh. Yesterday, I pronounced the marsh a success: butterflies in droves began "mudpuddling" on the moist marsh soil.
The system directing water off our roofs is simple. Rain runs down the roof, follows the gutter to the down-sprout and is soon streaming across lawn or sidewalk. Much of this rain then surges into our storm sewer system with its accumulated stock of motor oil, cigarette filters, pet waste, fertilizers and pesticides.
As with any project involving significant landscape change, before beginning to excavate, check with your homeowners' association and municipal government to make sure your intended marsh project is permissible.
My marsh project began to take shape in early winter, interrupted by periods of back strain and seasonal periods of frozen ground. Step one was to outline the perimeter of the proposed marsh.
My marsh is irregular in the outline. This is due more to encounters with bedrock than any sense of design on my part. I stripped sod from a 450 square foot area, then excavated the subsoil and rock to an average depth of 14 inches.
I connected my water source, a downspout from our roof, to a length of solid, flexible plastic pipe. This I angled down and away from the house so that water would enter the top of the marsh. The next rainstorm however, showed that the pipe angle was less than was necessary, and that my fill material was too porous. In April, I dug out the pipe, excavated the ditch with a greater angle and backfilled with clay.
Next, I prepared a soil mixture that contained some sand, a dozen buckets of compost, a good quantity of the original subsoil and a small pickup truck full of sand leaf mold. The marsh soil was mixed in a place with my tough, little rototiller. Areas of differing moisture were created by simply varying the original basin depth, then backfilling uniformly with my marsh soil.
The last and most enjoyable task was one of plant selection. As butterflies and hummingbirds rank high in my plans, I factored in their needs with questions of plant size, fragrance, hardiness, color, and seasonal interest. Spicebush, sweet pepperbush, buttonbush, silky dogwood, wafer ash and prickly ash now tower over cardinal flower, great blue lobelia, swamp milkweed and white turtlehead. Joe pyeweed looms over the downstream end of the marsh and provides a transition between the marsh and butterfly garden.
Nature soon took over as the landscaper of my marsh. As the shrubs grew, songbirds and cardinals, catbirds and thrushes took up residence. My labors now include watching the birds and butterflies visit the marsh, and digging up the progeny of the original planting as gifts to friends.