Rain gardens are low areas created to catch water runoff. They perform several functions.
• They act as a filtration system for water that runs off from streets or driveways or other polluted areas.
• They allow water to filter into the groundwater reservoir instead of running off into streams or the ocean. Enough of them could help refill aquifers that are being depleted.
• This groundwater catchment is generally not as vital in Florida, where aquifer recharge happens quickly and in numerous places, but can be very useful in Los Angeles, for instance, where precious water runs off into the ocean unless captured and allowed to soak in.
• They help prevent flooding by providing a catchment basin for water and directing its flow in a desirable direction. They capture the energy of water, but also guide its release from a site once the capacity is reached.
• Can provide an area for thirsty wildlife and native plants that can support pollinators. If capturing water that is not polluted, a rain garden can provide a place for moisture loving edibles such as bananas.
Permaculture designer and water specialist Brad Lancaster got the city of Tucson, Arizona to place curb cuts along streets that could send water into rain gardens that performed all of the above functions.
You can use a place in your yard that is naturally low to create a rain garden, or create one where the water runoff is the strongest. You can use pipes to send the water to a more appropriate place if the runoff area is not the best place. Often, gutter outlets are a great place for rain gardens.
Retention basins are a larger version of this concept. Often, they aren’t planted with natives or other plants that could help filter pollution or provide wildlife habitat. This is something that could change!
Planted with native trees and other vegetation, a large rain garden in Shoemaker Green, in Penn State, Philadelphia, allows stormwater to drain slowly into the soil. (Photo: Chloe Cerwinka/FRES)
Some cities are thinking more with the concept of capturing rainwater in various ways, filtering and cleaning it, and storing it in naturally existing aquifers. The retention basin design above retained older trees and added native species.
There are many ways we can incorporate rain catchment into our site in a way that increases the health not only of our site, but of our entire watershed. The more people that create these, the healthier the watershed will be. And they're beautiful!
Plants to choose for a rain garden should be able to take both wet feet and drought because they’ll experience both. Plant more dry loving plants along the upper lip of the rain garden, and plants that can stand in water for a time (however long it lasts in your rain garden) in the middle.
Some potential plants for rain gardens in Florida, most of them native: Blue flag iris, goldenrod, swamp sunflower, canna lily, crinum lily, day lily, spider lily, and swamp milkweed, fakahatchee grass, muhly grass, banana, wiregrass, Virginia willow, buttonbush, elderberry, or wax myrtle.
Some points to keep in mind when constructing a rain garden. Much of this is good advice for other earthworks as well.
Keep it at least 10’ from foundations and 25’ from your septic and drainfield.
• If your soil doesn’t drain well or you have excess water, be sure to design a way for water to flow out of your rain garden. If you don’t direct it, it will go wherever, which might be toward your house or something else you don’t want flooded. This could be as simple as leaving a spillway on the side of the garden where you want water to flow. A fast way to do this is to lower the lip of the garden at that section and place concrete blocks or bricks on the rim to line it (ensuring it is lower than the rest of the rim).
• Many people line the “dry creek bed” that leads to the rain garden with plastic liner or concrete. We don’t like to do that. We use banana leaves or thickly matted and stomped down grass clippings to slow the drainage in the bed, so that most of the water ends up in the retention basin. The less plastic, the better.
• Be sure to dig the basin at least 18” below where you want it to end up, and add organic material. This could be a mix of compost and wood chips or compost and sand, etc. If you add wood chips, the basin will sink even further once they break down, which could be a good thing depending on your design. Most Extension Services recommend things like peat moss which is very absorbent, but we prefer to use local materials.
• Be sure to not put the rain garden in a swampy area that stays wet for many days, or weeks or months. The idea is infiltration. That doesn’t mean you shouldn’t plant native swamp plants in the swampy areas, or bananas along the edges!
• If you don’t want to weed, plant intensively. Fill in the spaces. You can always remove plants if they get too thick.
• Plant layers - a small tree can really set off a rain garden.
Inspire your entire block to do a rain garden - it reduces flood pressure and beautifies the neighborhood.
This resource lists plants useful in a temperate rain garden. Many of these grow in a wide USDA range including Florida, and some are edible/medicinal. https://extension.psu.edu/rain-gardens-the-plants
More rain garden resources: https://extension.psu.edu/rain-gardens-the-plants
Hands On Activity
Walk your site and look for places where water naturally concentrates (from a rooftop or gutter, or in a dip in the land), and consider how you could capture it with a rain garden in the vicinity.