Rain gardens are a great way for homeowners and businesses to reduce polluted runoff from their property. Attractive gardens add value to the property, reduce time spent mowing and provide a shelter for area wildlife. To spread the word about rain gardens, DENR wanted to build one at the state fairgrounds in Raleigh. With help from our partners at the N.C. Department of Agriculture and Consumer Services, the N.C. State Cooperative Extension Service, its Master Gardener program and Logan’s Trading Company Garden Shop, we built the one you see here.

Our first step was the same as any property owner: find a site where water naturally drains. State fair and Cooperative Extension staff walked the fairgrounds and ended up very close to the existing ‘garden area.’ The site has a catch basin that collects stormwater, but this unfiltered water is full of trash and sediment. We placed the garden in front of the catch basin so it could filter the stormwater.

The size of the garden depends on the amount of rain it will receive. If the garden is fed from a gutter or drainpipe, you can measure the roof and use these calculations to size to size your garden.
The same simple calculations can be used for stormwater coming from a driveway or basketball court.

Now that you know how big an area you’ll need, take a look at what you’re standing on. If you live near the coast, you’re in luck! Sandy soil drains well and needs no amending. The rest of North Carolina is home to red clay, which doesn’t drain very well at all! To remedy this situation, do what we did at the fairgrounds. Dig a little deeper, then add sand and small rocks to help drainage.

For all gardens, build up the edges a bit to hold the water and then flatten them slightly on the downhill side. Most rain gardens are designed to hold a one-inch rainfall (a nice average for most of North Carolina) but need to accommodate overflows. By flattening the downhill side, overflowing water will “sheet” across the soil instead of channeling an erosion-causing furrow.

Ready to start digging? Find a few friends and it will go faster. Backfill the hole with the soil you just displaced or add topsoil. Whatever you do, don’t fill the hole flush to the ground. Leave a bit of a bowl for water to collect and enough depth to mound the soil slightly at your plantings. Rain gardens should rain slowly, but not take more than three days to empty. If yours takes longer, add more sand and rocks to improve drainage. If that doesn’t do the trick, make the bowl shallower. Mosquitoes start breeding after three days and while we do want a natural habitat shelter, skeeters are not exactly an endangered species!

Native plants are definitely the way to go with these gardens. The fact they are already used to the climate is just the buffer you need for health because these plants will also be called upon to live in very wet and very dry conditions. That’s a lot to ask of a plant, so ‘go native’ and save yourself some expensive replanting. Here’s a list of what’s native to your area. Plants can be mulched or grass can be allowed to grow – your choice! If you do choose mulch, go for the shredded hard wood – pine bark floats just away!

The last step sounds a bit backwards, but it’s true – you have to water the garden! At least until the plants get established or Mother Nature decide to rain on the old North State again. If your area is operating under water restrictions, observe them. But take heart for the future. If there’s even a little bit of rain in your area, your rain garden will be the last part of your yard to dry out.

Build Your Own Rain Garden (power point presentation)