Rain gardens recycle runoff into water for plants, providing myriad benefits. Draining excess rain protects your building's foundation, helps restore underground aquifers, processes chemicals and bacteria caught in runoff, and prevents bugs from setting up breeding grounds near your home. To turn your yard into an oasis where plants can deliver these miracles while blossoming into bushes for wildlife, flowers for bees, or delicious herbs for your kitchen, follow these simple steps.
Step 1 - Plan Your Rain Garden
To find the ideal location, use a level and a straight board to determine where your yard has a slope. If the yard is completely flat, you’ll need to create a sloped area or drainage ditch to guide the water where you want it to go. For optimal flow, the slope should be at least one inch for every four to five feet.
Rain gardens are most effective when they're located near low points, driveways, sidewalks, and downspouts. The garden should be a minimum of 10 feet from your house to avoid any risk of rot or flooding. If you want to guide rain more directly, you can run PVC pipe underground to channel rainwater from one or more gutter spouts.
You may also opt to lay river rock or other large landscaping barriers to direct water. You can build a berm in the low spot and add swales (slightly sunken channels) to help direct water runoff from the higher areas of the yard. Avoid placing a rain garden over any underground utility lines or septic tanks.
Step 2 - Test Your Drainage
Once you have a spot picked out, you’ll want to determine how deep to plant your rain garden. This will depend partly on the absorption rate of your soil, as you only want your garden to collect the amount of water it can absorb over about two days.
Test your soil by digging a hole, filling it with water, and timing how fast it drains. If the level goes down about half an inch each hour, the garden will absorb about one inch of water every two hours, or 12 inches in 24 hours, so a six to twelve inch depth should facilitate drainage over one to two days.
If your soil is draining very slowly, you may want to change its mix to include more peat moss, compost, and/or sand. Depending on how much precipitation your area gets, you may want to place some rocks around the edges of your garden to assist with drainage in case of overflow.
Step 3 - Pick Your Plants
Native plants will perform the best in rain gardens, so choose flora that thrives in your zone. Popular options include sedge, sedum, daylily, artemisia, aster, and cornflower. Plants with deep root systems, like wildflowers, shrubs, and grasses, also tend to thrive in occasionally high-moisture environments.
Place plants with lower water requirements along the higher edges of your garden. Remember, you don’t want plants that need to stay wet all the time, since your goal is to create a garden that drains all the rain out in a day or two.
Step 4 - Plant
First year care is crucial to get started on the right foot. Incorporate some sand, mulch, fertilizer and/or compost into your planting soil, to maximize drainage and nutrition. Shredded hardwood mulch is a good choice, since it's heavier than wood chips and pine bark, which will float out of the garden when it fills. Your young plants will be setting up their root network, so you don’t want to let the ground become over-saturated, leading to root rot.
If you notice your new garden taking more than 48 hours to drain, dig a small hole in the berm on the lowest portion of the rain garden to allow some water to flow out. This will help keep young plants from absorbing too much water too soon. Adding decorative rocks at the incoming edge of the garden will also help keep your baby plants from washing away.
During the dry season, make sure your garden gets about an inch of water each week. Other than that, your native rain garden should require very little attention to remain healthy and productive for years to come.