What is a Rain Garden?
A rain garden is a flat bottom depression in the landscape that captures rain water runoff or snow melt from impervious surfaces like parking lots, trails, roofs, and driveways then slows and cleans the runoff and allows it to be absorbed and filtered into the ground. Rain gardens help to filter out pollutants before they can reach our ponds, wetlands, and Mississippi River. Rain gardens are a part of a green infrastructure that helps beautify our community, improve our environmental water quality and provide food and shelter to our wildlife.
Benefits of a Rain Garden:
• Help to filter out pollutants such as fertilizers, heavy metals, sediment, pesticides and herbicides, pet waste, oils and chemicals before they reach our protected waterways.
• It is a pollinator habitat and provides a food source for hummingbirds, butterflies and honey bees.
• Helps with flood protection by allowing water to be absorbed in an area that is designed to filter and drain over a two-day period.
• Provides cool water recharge to ponds, wetlands and rivers.
• Recharges aquifers by allowing water to soak into the ground.
• Helps with water conservation since water can now be utilized by the surrounding vegetation instead of directly flowing into the City’s storm sewer system and get carried to the nearest water body.
• Beautifies the community with natural landscape.
• Replaces lost wetlands.
• Better mimics the natural environment prior to development.
Anatomy of a Rain Garden
Inlet: The area in which water runoff enters the garden, the type can vary depending on the function. Some inlets are simple slopes of grass or pavers that are angled down to allow water to flow into the garden, while other inlets look more like a catch basin in the curb of the road.
Ponding depth (aka above ground storage volume): The area at the bottom of the garden in which water accumulates and begins to slowly drain into the ground within a 48 hr period. The depth will vary from garden to garden depending on the expected water volume it will receive.
Mulch Layer: Mulch is recommended to be double shredded hardwood, so as to not float away in heavy rain events and be at a depth of 3” to help keep weeds away and lock in moisture.
Overflow or Outlet: The area in which water can escape if the garden becomes too full during a heavy rain event.
Rain Garden Soil Mix (aka engineered soils): A mix of soil, usually 80% sand and 20% compost. The compost will support plant growth, while the sand will help water infiltrate.
Draintile: A pipe, usually made of PVC, that is perforated to help water soak in and flow to the outlet. This is connected to a knife valve that allows you to open and close the draintile when needed. The knife valve can be opened if the garden is not able to drain within a specified amount of time, otherwise it should usually remain closed.
Interested in a Rain Garden of your Own?
Its the City's recommendation to before constructing your own rain garden you attend one of the Clean Water workshops. Landscaping for Clean Water workshops are hosted by the Dakota County Soil and Water Conservation District in conjunction with the City of Inver Grove Heights. The workshops provide an overview of water quality challenges in Dakota County and provide beautiful and practical ways of reducing runoff pollutants that are causing issues.
The Landscaping for Clean Water program makes it easy to realize the positive impacts rain gardens, native gardens, and shoreline stabilizations can have on your aesthetic and environmental surroundings. Participants receive design assistance for a project at their home and are eligible for a $250 grant toward the installation of their rain garden project.
The City recommends following the City’s standard detail which is a plan that outlines what material to use, slope steepness, dimensions, pipe size etc. when constructing your rain garden.
Raingardens can be a beautiful landscape feature, selecting the right type of plants is very important to ensure the garden functions properly. Factors such as the size of the garden, amount of sun or shade, type of soil, number of desired plant varieties and amount of water that will be received, will all determine the types of plants you should have in your garden.
The Blue Thumb selector tool can help you decide on the plants for your garden
Raingardens need to be maintained just like any other landscape planting, with regular care and nurture.
Ways in which to care for your raingarden include:
• Regularly removing weeds by hand not by herbicide.
• Watering often for new and growing plants or on hot/dry streaks for mature plants
• Maintaining 2-3 inches of mulch throughout the basin, to help keep weeds at bay and lock moisture in.
• Pruning plants that need to be cut back or trimmed.
• Replacement of dead plants.
• Cleaning out your inlets and pavers to ensure water can flow into the garden properly.
• Remove excess sediment and debris from inside the garden.
• Remove small volunteer trees from within 10 feet of the garden.
• Ensuring your garden continues to drain within a 48-hour period.
• Ensuring there is no erosion occurring in or around the garden.
For more information on raingardens check out these sites: