Planning your rain garden is an important step and should not be overlooked. For most residential settings, you will be trying to capture runoff from your house roof and directing it to your rain garden. This can be accomplished by piping the downspout directly into your garden,or by letting it run over grass before entering the garden. Here are several points to consider when choosing the site in your yard.
1. Avoid placing the rain garden in a low spot in the yard that always seems wet. A rain garden is not a water garden or a wetland. Placing it poorly drained soils may lead to slow infiltration and unwanted long term ponding.
2. Keep your rain garden at least 1O feet away from your house if you have a basement. Infiltrating water close to your foundation can lead to water problems in the basement.
3. Do not install a rain garden in an area where bedrock or stone outcrops are closer than 2 feet to the surface.
4. Place your rain garden at least 25 feet away from wells and septic systems. Rain gardens placed downnhill from a septic field should be at least 50 feet away. Rain gardens placed too close to these areas could cause unwanted infiltration into drinking water, add excess water to a septic field, or collect septic effluent.
5. Avoid steep slopes. Rain gardens can be installed using a retaining wall design on moderate slopes, but the construction of this type of garden is more complicated.
6. Plan for overflow from the garden. Although your garden will be sized to contain the most frequent storms, it will likely not contain the increased volumes of water from larger storms. In most cases the garden will overflow to your lawn, but just make sure overflow is not directed towards your foundation.