Photo courtesy of Missouri Botanical Garden
The Missouri Botanical Garden's example of how to do rainscaping right.
Even rain’s complicated these days. It used to fall and soak into the ground. Now it comes in sudden torrential downpours that cascade from roofs and run off streets and driveways, carrying their filth into the yard and leaving it soggy and puddled.
Strategy? Rainscaping.
If your only problem’s mild eco-guilt: Get a rain barrel already. Just tuck it under a downspout. Make sure it has a convenient nozzle so you can fill your watering cans with the lovely rainwater you’ve collected.
If there’s a tiny creek running through your lawn after a storm, or the puddling is ruining your yard and your dress shoes: Put in a rain garden. The Missouri Botanical Garden has a tutorial all ready for you.
Ideally, your rain garden will be on a gentle slope, uphill from the lowest point in your yard. Dig a basin (it can be oval, or shaped to complement other beds) that will hold about 6 inches of water at its deepest part, then taper up to 2 inches or less at the edges. How big should your rain garden be? About one-fifth the size of the area you’re draining, according to a recent USGS study.
Note: if you don’t have a slope, make sure the soil’s well drained, and use a circular or square shape. If your slope is long and narrow, you might try a series of small gardens stepped along the slope. You can even connect them with a bioswale (a fancy word for a slope-slided drainage ditch, or channel, filled with vegetation). You can design your swale like a dry stream bed, using rocks and grasses to slow the water’s flow.
Your soil matters—if it’s the heavy clay so common in our city-built-of-brick, do a percolation test to make sure there’s enough drainage and you’re not just creating a pond. Dig a hole 6-inches deep and 6-inches across, right in the middle of your future rain garden, soon after a heavy rain. Fill the hole with water. If it’s gone 24 hours later, you’re fine.
If you’re excavating all the soil, you can replace it with a rain garden mix. But do not till it into existing soil, because its sand will mix with your soil’s clay and compact like concrete.
Once you’ve dug your basin, build a berm (a low mound of soil) at the far side, to hold the water. If your slope is steep enough that water will rush in, reinforce the area where the water will enter with erosion netting and/or stone. Avoid using shredded bark or other organic mulches that will easily wash away; use stone and gravel instead.
Now for the fun part: Choosing your plants. A rain garden can be in sun or shade; you’ll just have a wider selection of plants if it’s in the sun. In one of his designs for MSD’s Rainscaping program, landscaper Joseph Heller, owner of Simply Sustainable Landscaping, planted the berm with cardinal flower, a perennial a few feet tall. At the deepest part of the basin, he planted southern blue iris, a Missouri native that can grow to 4 feet; other options are rose mallow (hardy hibiscus); and, as ground cover, soft rush, a bluish grass that tops out at 3 feet. In the shallower areas, he planted crested iris (“That’s a wee short one”) and also suggests orange cone flower, for a late-season splash of color, and meadow phlox, with oak sedge as an efficient ground cover.
There’s an abundance of ideas on the Missouri Botanical Garden Native Plant List.
If you’re worried that your rain garden will look disheveled, as though nature really has taken its course, just keep the weeds under control for the first year or two, until your plants can hold their own, and give the garden a clean edge, either with a path or just a cleanly mowed boundary. You can also add a low fence, stones, or a bench.
