Rain Gardens FAQ

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Q: Can my Rain Garden be on a slope?
A: Yes, but the goal is to keep the garden itself level. Digging a rain garden on a steep slope will require bringing in extra topsoil to bring the down-slope part of the garden level with the upper part. Putting the rain garden in a flatter part of the yard will make digging easier.

Q: How do I determine the slope of the yard where I want to build my rain garden?
A: Place a stake on the uphill and downhill ends of your rain garden location. Attach a string to the bottom of the uphill stake and, using a level, attach the string to the downhill slope so that the string is level. Measure, in inches, the distance between the stakes (A) and also the distance on the downhill stake between the ground and the level string (B). To find the area’s slope percent, divide B by A and multiply the result by 100.

Q: How deep should my rain garden depression be?
A: That depends on how much the yard slopes in the area where the rain garden will be. On a level yard or one that slopes less than 4%, the depression should drop about 4” to adequately contain the volume of water. On a slope of 5% to 7%, 6 “ to 7” below the up-slope s about right. If the slope is between 8% and 12%, it is easiest to build it 8” below the level of its up-slope. If the slope is more than 12%, it is best to find another site or speak to a professional landscaper.

Q: With my rain garden on a slope, can I prevent the rain water from running off the lower edge?
A: Rain gardens on a slope should have a berm on three sides to hold the water during a rainstorm long enough for it to soak into the ground. As you are digging soil from the uphill side of your site, heap this soil around the edge where the berm will be. The berm will be highest on the downhill side and taper up the sides. On a steeper slope, additional soil may need to be brought in to create the berm.

Q: How do I prevent erosion from the downslope of the rain garden?
A: To prevent erosion, ensure that the berm is high enough and well-compacted so it does not break down in a heavy downpour. You can plant grass on the berm or cover it with mulch to further prevent erosion. (Cover grass seed with straw while the grass is taking root.)

Q: Should I add soil amendments to the existing soil?
A: Compost will help your plants become established. If you do add compost or other soil amendment, dig the garden a bit deeper to accommodate the additional material

Q: Will my rain garden become a pond?
A: No. The rain water will soak in so the rain garden will be dry between rainfalls. (Some gardens can be designed to have a permanent pond, but construction of a pond is not addressed in the manual)

Q: Will my rain garden require a lot of maintenance?
A: Some weeding and watering will be required in the first two years. After your plants are established, the rain gardens can be maintained with little effort. You may have to perform some thinning in later years as the plants mature.

Q: Can I incorporate elements other than plants?
A: You might consider enhancing the rain garden by using local stone, ornamental fences, benches or other ornamentation to give the new garden an attractive look as part of your yard and neighborhood.

If you have other questions about the 1,000 Rain Gardens Initiative, or rain gardens in general, please contact Barbara O'Connell at (803) 684-3137 ext. 101 or email at barbara.oconnell@sc.nacdnet.net Thank you for your interest in the program, and happy rain gardening!