A rain garden is a garden of native shrubs, perennials, and flowers planted in a small depression, which is generally formed on a natural slope. It is designed to temporarily hold and soak in rain water runoff that flows from roofs, driveways, patios or lawns. Rain gardens are effective in removing up to 90% of nutrients and chemicals and up to 80% of sediments from the rainwater runoff. Rain gardens incorporate native vegetation; therefore, no fertilizer is needed and after the first year, maintenance is usually minimal.
However, not every yard has a good spot for a rain garden.
What is the average size and placement of a rain garden?
A rain garden should have an area about 20% the size of the roof, patio, or pavement area draining into it. A typical rain garden for a residential home or small building is between 100 and 400 square feet. Regardless of the size, big or small, each rain garden can make an impact.
Rain gardens are shaped longer than they are wide and positioned perpendicular to the slope of the land in order to catch the maximum amount of rainfall. Rain gardens should be placed at least 10 feet away from building foundations and should not be located where water ponds for an extended period of time.
What makes a site suitable for a rain garden?
- The site is fed by one or two downspouts
- Soil tests show the site does not have heavy clay soils (conduct a ribbon soil test)
- Infiltration tests show the site infiltrates water one-half inch per hour or more (conduct an infiltration test)
- The water table is at least 2 feet from the surface at its shallowest
- The slope of the site is not more than 12%
- The site is at least 10 feet from buildings with basements
- The site is not over any utilities (contact your local diggers hotline)
- The site is not over or near a septic tank, drainfield, or wellhead
- The site does not interfere with any trees. If there are trees in the area, make sure they can handle wet soil conditions for lengthy periods of time.
- If the site that you have chosen does not meet all of the above criteria, it does not necessarily mean that a rain garden cannot be established there. Speak with a professional landscaper to review your options.
What is the typical cost to design and install a rain garden?
The cost of a rain garden is dependant on the property’s soil type, the size of roof/driveway/patio draining into a rain garden, and the types of plants chosen. If the soil is high in clay content, it may be a good idea to install an under drain system to prevent standing water in the rain garden for more than 48 hours.
For a self-installed rain garden, expect to pay between $3 and $5 per square foot in plant costs and soil amendments (peat moss, for example, should be mixed in to soil with high levels of clay). When working with a landscaping company to design and install your rain garden, the cost will significantly increase to around $10 to $15 per square foot.
What kind of maintenance does a rain garden require?
When native plants are used, your rain garden will not require pesticides or fertilizer. As the rain garden is establishing during the first and second year or during periods of little to no rainfall, occasional watering of the plants may be necessary. Likewise, weeds will need to be removed while dead plants may need to be replaced. Once the plants in the rain garden have become established and grow larger, they will eventually out-compete the weeds.
Can I do it myself?
Absolutely! Building it yourself will save you money and provide you with a greater sense of accomplishment. Many homeowners finish their rain garden in one afternoon. Digging the garden is the most time consuming task, as 6-8 inches of soil depth is typically removed to add amendments. Involve your entire family or invite the neighbors over and make a party out of it.
To get started, we recommend you conduct a soil test and an infiltration test. You can do both of these tests yourself which will ensure the success of your rain garden. Find out how to conduct these tests and find more resources at www.groundwater.org/action/home/raingardens-more.html.