LSU AgCenter Horticulturist
The rain has been pouring for nearly a week, causing flooding in parts of the state. One day brought 13 inches as the weather systems stalled over some cities. Many areas have been under water for days.
One thing this weather has definitely shown us is where the problem spots are in our yards. Take this opportunity to identify these areas and address them for the future.
Floodwaters can carry pet waste and dangerous chemicals that can leave a residue on your fruit and vegetables. They also can spread harmful bacteria such as salmonella. To be safe, throw away any produce that was under water. If the plants dry out and survive the flooding, eat the next round of fruit that they bear.
Next, take note of any low areas in your lawn that collected water. Take pictures so you can remember where the area is after it drains and all evidence is gone. You’ve got a few options for what to do in these areas.
You can have additional drainage installed or divert the water to a storm drain or pond, but not toward your neighbors’ property. You can make a drainage swale by digging a shallow trench and filling it with rocks to prevent soil erosion. The trenching needs to be in a downward slope that drains the water away from the area where water is pooling.
A more expensive but worthwhile investment is to have a French drain or dry well installed. Both are installed below the topsoil to redirect the excess water.
There are some differences between the French drain and a dry well. A French drain is typically a long trench filled with gravel with a drainage pipe running from the house down the length of the drain and is covered up with soil or river stone at the grade level.
A dry well is used to collect water and release it to the surrounding soil instead of redirecting the water to another area. It is placed at the end of a swale or French drain and is constructed of drainage fabric or a large metal or concrete basin with holes in its sides through which the collected water can drain out into the nearby soil.
You can make a combination of the above options: connect a French drain to a downspout, and lead the water away from the house to collect into a dry well. However, if your soil does not drain well, a dry well will not be very helpful.
If you live in an area that has poor drainage with low areas and no sloping, it will be difficult to correct without major groundwork. If this is the case in your yard, you can try a rain garden. This option works with Mother Nature rather than against her.
A rain garden is a low area in the landscape that is dug to collect rainwater and allow it to soak into the ground rather than enter the storm sewer system. Rain gardens help decrease soil erosion and reduce the amount of suspended solids and pollution in our waterways.
Rain gardens often use native and other water-loving plants that can tolerate standing water. Some great selections for Louisiana are bald cypress, river birch, live oaks, swamp red maple, pond cypress, rushes, sweetbay magnolia, southern magnolia, ironwood, parsley hawthorn, Virginia willow, American beautyberry, yaupon holly, Florida anise, dwarf palmetto, southern wax myrtle, Louisiana iris, buttonbush, river oats, muhly grass, ironweed, golden rod, cardinal flower, cinnamon fern, Texas star, swamp mallow, swamp milkweed, rudbeckia, rain and crinum lilies, and so many more.
Locate a place for the rain garden 10 feet away from the house and 50 feet from septic tanks. Dig a hole 2 feet deep, then time how long it takes for 8 to 12 inches of water to disappear. If 10 inches drains in 14 hours, the drainage rate is 10 inches divided by 14 hours, or 0.71 inches per hour. Your target rate is 0.5 inches per hour or greater for an 18-inch-deep garden.
If the area drains at a rate lower than 0.5 inches per hour, you need to dig 30 inches. If the rate is less than 0.1 inches per hour, the area is not suitable for a rain garden.
Make the area the size that you want and in any shape. I like a kidney bean shape or oval. Mark the area with a garden hose, and begin digging down to 6 to 8 inches deep. You can use some of the soil to create a small berm to help retain water.
Make a trench, lay a flexible corrugated tubing from the downspout and run the length of the trench to carry the water from the roof to the rain garden. Make sure the pipe extends 1 foot into the garden. Use stones or rocks to line the trench to prevent erosion, and cover the pipe with soil or leave it above ground.
Fill in the area with soil. Add sand, organic matter or compost to improve drainage. Next, add plants that tolerate the most water to the center and those that like less water to the outer edges, which will be drier. Mulch to help prevent weeds.
Take this opportunity to note the low areas that hold water in your yard and make a plan to help improve drainage. Photo by Heather Kirk-Ballard/LSU AgCenter
Native grasses and sedges make excellent plant selections for rain gardens. Photo by Ashley Edwards/LSU AgCenter
In addition to being a great rain garden choice, Louisiana irises sport beautiful, colorful blooms. Photo by Heather Kirk-Ballard/LSU AgCenter
Virginia sweetspire is a great shrub selection for rain gardens. Photo by Heather Kirk-Ballard/LSU AgCenter