Interview with Ginny Stibolt
Many people today are tuned in to the fact that water is a precious resource we need to protect and use wisely, and rain barrels are being put to use in many yards. But what the heck is a rain garden?
A. A rain garden, also known as a bio swale, is planted in a swale or a low area where rainwater is directed. The purpose of rain gardens is to retain more stormwater on our properties where it then has a chance to percolate into the ground and isn’t whisked away into the stormwater systems. The swale could be natural or manufactured by digging and building berm around the area. It should be located where you can direct rainwater from roadways, driveways, parking lots, downspouts, and/or rain barrel overflows to it. The swale should not be seasonally or perpetually wet without the rainwater, and the swale should not be dug under existing mature trees.
Q. Why not use a wet spot in the landscape for a rain garden?
A. You could certainly plant rain garden plants in that low spot and they would be far easier to take care of there than a lawn. But it's probably not a good idea to actually direct more rainwater there, especially if it's from a parking lot or roadway, because this is an intersection with the water table and you don't want to introduce pollutants (drippage from vehicles) into the water table. You could build a rain garden "above" the low spot so that only filtered rainwater would reach it. Treat a pond this way as well--install rain gardens so rainwater is slowed down and filtered before it reaches the pond.
Q. How much space is needed for a rain garden?
A. Your rain garden can be large or small and can be tucked into many places in your landscape, but standing water should be gone within three days to prevent mosquitoes from breeding there. A rain garden should be located so the extra water in the soil won't undermine the foundation of a building. If your rain garden space is small compared to the rainwater it receives, you'll probably want to dig a good-sized drywell as part of its construction so the water will have a place to go. You need to plan for the overflow for the rain garden, no matter what its size, because a heavy storm or hurricane will overwhelm its capacity. The overflow should be directed away from buildings toward an area in your landscape that can absorb extra water like a wooded area or even a lawn.
Q. What kinds of plants will I need for my rain garden? Do they have to be native? Will it be hard to find plants?
A. Rain garden plants need be able to live in standing water and also withstand drought. The plants I recommend are natives, because they are more in tune with our wet and dry seasons, but some non-natives could also work well. While it's not recommended that you dig a new rain garden under a tree, trees are good additions to large rain gardens because the larger the biomass of your plants, the greater the rate of transpiration (evaporation of water through the leaf pores), so the standing water is more quickly absorbed.
Some recommended trees and shrubs: Bald & swamp; pond cypress, beautyberry, buttonbush, cabbage palm, dahoon holly, dwarf swamp; saw palmettos, elderberry, inkberry, wax myrtle, sweetbay magnolia.
Some recommended perennials: Black-eyed Susan, blue-eyed grass, dixie iris, goldenrod, meadow beauty, netted chain fern, rain lily, royal fern, rushes, sedges.
These are mostly easy-to-find plants and should be available from most any native nursery.
Q. What happens to my rain garden during dry spells?
A. The plants you want in your rain garden should be drought-tolerant so they'll go through a dry year without any irrigation. This is why natives are usually recommended. Annuals are not a good idea for rain gardens because they don't have time to develop a deep root system.
Q. How do I keep grass or other weeds out of my rain garden?
A. Weeds might be a problem for a year or two, but you can reduce weeds by mulching between your plants. But don't mulch with materials that will float such as bark nuggets. You may need to hand-pull weeds for a while, but after a year or two, the rain garden plants should spread out enough to shade the ground. And consider any non-invasive plant that grows there voluntarily as a good candidate to add to your collection. Meadow garlic volunteered in one of my rain gardens and I've left it as a good addition since it's doing well.