What is a Rain Garden?
Rain Gardens are small basins that collect rain from sump pumps, driveways, lawns and downspouts. The idea is to correctly landscape a subtle “well” shaped basin to catch flowing rainwater. These rain gardens typically utilize native grasses and flowers that thrive in a wet environment.
Advantages of a Rain Garden
Rain gardens are designed with the Low Impact Development (LID) concept. A rain garden can be used as an alternative fix (cheaper/faster) to help alleviate water problems closer to the source, unlike traditional draining methods. By installing a rain garden, the property owner will not only have a sufficient low cost/low impact esthetically pleasing functional piece of landscaping but the amount of water pollutants will decrease because of the filtration properties of the garden. However, because of the relatively small volume of stormwater that a rain garden can detain, there should not be the unrealistic expectation that a rain garden will solve a major flooding problem.
Sizing and Sitting of a Rain Garden
Rain gardens are commonly located in two places: near the house to catch roof runoff and sump pump discharge or farther out on the lawn to collect water from the sump pump discharge, lawn and roof.
- Keep garden at least 10 feet from house so infiltrating water doesn’t seep back towards the foundation.
- Rain garden should not be installed over septic system.
- Putting the rain garden in a flatter part of the yard will allow for easier excavation.
- Locating in sunny area is best.
- Water should be channeled using a natural drainage way, constructed swale or a 4” PVC pipe placed in a backfilled trench that connects down spouts to the garden.
- Mulch should be used 3”- 4” deep through out the garden (provides weed protection)
- A berm should be built on the edge of the garden facing the street or nearest catch basin incase of overflow
Size of a rain garden will depend on three important factors:
- How deep the garden will be.
- The type of soils the garden will be placed in.
- How much roof/lawn will drain to garden.
1. A typical rain garden is between six and eight inches deep. These dimensions maintain a balance so as to prevent tripping hazards, visual appearance, and water storage. The depth also depends on the slope of the lawn.
- If slope is less than 4%, build the garden 3 to 5 inches deep
- If slope is between 5 and 7%, build one 6 to 7 inches deep.
- If the slope is between 8 and 12%, build one about 8 inches deep.
2. Before installation begins, identify the type of soil that the garden will be placed over. The most typical soil in Palatine is a heavy clay which do not drain very well. Therefore a deeper garden with a course gravel layer on the bottom followed by a sandy topsoil mix with a loose topsoil layer on the top should work best. Otherwise the
- Clay soils suitable for rain gardens should be able to drain about 6” of water within 24 hours. Dig a hole about 6” deep where the rain garden will go and fill the hole with water. If it takes more than 24-hours to soak in, the soil or location is not suitable for a rain garden.
- Gravel, sand and peat moss can be used in the rain garden to improve infiltration.
3. The last important factor to consider in determining the size of a rain garden is the area that will drain into the rain garden. The bigger the area of the lawn/roof being drained, the bigger the area of the rain garden should be.
- To calculate the amount of water that needs to drain from roof or watershed area, measure the roof area that will be facing the rain garden
- The total rain garden area should be at least 60% the area of the contributing roof watershed to enable proper infiltration
Developing Species List
Native plants work best in rain gardens oppose to typical Garden Variety plants seen in flower gardens. Plants within the rain garden develop deep root systems that help rainwater drain much faster through the soil. Allowing rainwater to infiltrate into the ground more efficiently will filter out harmful pollutants that would otherwise pass into the storm sewers and potentially down stream creeks and rivers. The following is a list of suggested plants suitable for this area along with their light preference.
Light Preference: Shade
||Spring to Summer
||1' - 2 '
||1' - 2 '
||2' - 5'
||1' - 3'
Light Preference: Partial Shade and Sun
- A variety of perennials and grasses should be used in the rain garden, 5 to 10 different species of plants will create a variety of color and improve the longevity of the rain garden.
- Include at least 25-30% grasses or sedges interspersed throughout the garden. They provide structure and support for some of the larger fobs which need the support.
- Generally, place the taller plants towards the back of the rain garden and shorter plants towards the front. If there is no clear front and back then place the taller plants towards the center and the shorter plants towards the periphery.
- Space plants at least 12” – 18” apart as most native plants mature to a large size within 1 -2 years after planting.
- During routine weeding and maintenance, be particularly attentive to removing invasive species of plants like Canada Thistle, Teasel and Reed Canary Grass – they can quickly take over new plantings if not controlled.