Choosing the Proper Site
- Dig a hole to test the drainage of your intended site.Jupiterimages/Photos.com/Getty Images
A rain garden collecting roof runoff should be located about 10 feet from the house foundation and the downspout, on a flat or slightly sloping site; do not locate the rain garden in a wet area, over a septic field, over a well or near large trees.
Since good drainage is the most important factor in constructing a rain garden, conduct a simple drainage test at your site. Dig an 8-inch deep hole and fill it with water. Let the water drain out then refill it. If the refill water drains out within a few hours, your site is suitable for the rain garden.
- River stone slows the water flowing into the rain garden.Jupiterimages/Photos.com/Getty Images
According to the Fall, 2010 newsletter of the Native Plant Society of New Jersey, a rain garden of approximately 4 feet by 7 feet should be sufficient to collect the water from one roof downspout Mark out the garden on the ground with marking paint or a rope.
Slice off the sod with a shovel and dig the garden area down 6 to 9 inches, setting aside the soil. The bottom should be flat with sloping sides. Create a mound or berm on the back and sides with the extra soil, leaving an area open toward the downspout. The berm will help retain rainwater in the garden. Construct a low area in one part of the berm to allow for overflow in periods of high rain. Locate this overflow so it drains into an existing drainage area in your yard.
To prevent soil washout, place some flat stones or river rock where the water enters the garden from the downspout and where it leaves through the overflow. Dig a shallow trench or swale to direct water from the downspout to the garden and line it with river rock, stone or the sod removed from the garden area.
- Cardinal flower can be used in a sun to part shade rain garden.Stockbyte/Stockbyte/Getty Images
It is important to select plants that can tolerate both wet and dry conditions. Native plants are the best choice since they are adapted to your local environment, but non-native garden plants can also be used. Use a variety of shrubs and perennials of differing heights and colors to add variety. Also add perennials or grass to the berm to prevent it from washing out. After planting, mulch the garden with 2 to 3 inches of shredded hardwood mulch.
The following plants are suitable for a rain garden:
Perennials: cardinal flower (Lobelia cardinalis), turtlehead (Chelone glabra), blue flag iris (Iris versicolor), black-eyed Susan (Rudbeckia hirta), blazing star (Liatris spicata), swamp milkweed (Asclepias incarnata).
Grasses: sedges (Carex sp.), switchgrass (Panicum sp.).
Shrubs: inkberry (Ilex glabra), Virginia sweetspire (Itea virginica), fragrant sumac (Rhus aromatica), spicebush (Lindera benzoin).
- Water your plants immediately after planting and every two to three days for the first season depending on rainfall and temperature. After they are established, water in times of drought and/or high temperatures as needed. Regular weeding, pruning and mulching will also be necessary.