Rain Gardens: Natural Processors of Runoff Pollution

Landscape MaintenanceLawn Care

Rain gardens provide a solution to the problem of runoff-transported pollutants in streams and ponds. Native plants that grow in rain gardens put down deep roots that act as filters, removing 90% of the chemicals carried by runoff from roofs, driveways, and lawns.

As Florida homeowners know, Florida lawns receive lots of rainwater, especially during the summer. Some rain soaks into the grass, while much runs off into ditches and drains. This runoff contains chemicals, oil, and debris from roofs and driveways, plus fertilizers from lawns. These pollutants travel with rainwater through drains and into local streams and ponds.

One solution to the problem of polluted rainwater runoff is the rain garden. What is a rain garden? It’s a planting of native vegetation in a small depression–a feature designed to slow down, temporarily collect and filter stormwater runoff.

Why Plant a Rain Garden?

Less Pollution
A surprising 70% of pond water pollution comes from the chemicals and debris carried by rainwater runoff. A rain garden will remove 90% of chemicals and 80% of sediment from runoff. The plant-filtered water percolates through the soil and down into groundwater aquifers.

No Mosquitoes
Rain gardens drain within 12-48 hours and are dry most of the time, so they eliminate the problem of standing water after a big storm. This means that they reduce mosquito breeding areas around yards and homes.

Planning Your Rain Garden

Choose a Site
A rain garden should be located at least 10 feet from the nearest building foundation on a slope that is not more than a 12% grade. An area that receives water from one or two downspouts is ideal.

Check the soil and make sure your site does not have heavy clay. This is more of an issue in North Florida than in the rest of the state.

Plan the Appropriate Size
Typical rain gardens for residential homes are between 100 and 400 square feet in size, but a good rule of thumb is to create a garden that is 20% of the size of the roof and pavement areas that will drain into it. To collect the most runoff, your garden should be perpendicular to the slope of the land and longer than it is wide (think oval or kidney-shaped).

Check Before You Dig
Make sure the site of your rain garden is not over utility lines or near a septic tank. Position a rain garden near a tree only if the tree will tolerate wet soil conditions for long periods of time.

What To Plant in a Rain Garden

Native vegetation is the way to go. Native plants are low maintenance and do not need fertilizer as they are naturally adapted to a range of moisture conditions and efficiently use the water and nutrients found in the soil. The root systems of native vegetation are perfect for holding and filtering water: 80% of a native plant’s mass is underground.

Next, think about where to position plants in the garden. Plants in the center will experience more standing water, so they should be species that thrive in wet soil conditions. Plants around the edges will often not be in wet soil and should be drought-tolerant.

Get Going!

These tips should help get you started in creating your rain garden. Visit your local nursery for help in assessing your soil and choosing the appropriate native plants for your area.

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