Rain gardens in Florida

Stormwater carries pollutants that
end up in our waterways.

Why do we need rain gardens?

Sequestering stormwater reduces pollution of our waterways and of our aquifers. This is because stormwater runoff carries: fertilizers, sediments, plant matter, manures, pesticides, herbicides, salts, oils and other vehicular drippage. 

Pollution that originates from numerous, diffuse sources, such as our yards is called Non-Point-Source (NPS) and the Environmental Protection Agency (EPA) estimates that NPS pollution is the largest threat to our waterways. But, we can reduce NPS pollution from our yards and from our communities by holding or sequestering more rainwater by installing rain barrels and by building rain gardens.

Sequestering rainwater

Installing rain barrels and rain gardens are 2 effective ways to retain rainwater.

Rain gardens can serve as
overflow basins for rain barrels,
 lined ponds, or bog gardens.

Rain barrels collect and store rainwater, which can be used in many ways in the garden and elsewhere where purified tapwater is not needed or desired. For example, rain barrel water is good for irrigating plants, washing vehicles, pre-rinsing root vegetables, or pre-rinsing muddy clothing or muddy tools. 

Details on rain barrels, including how to hook them up for various situations, are found in several other articles I have written. Start with this one, which includes links to others. Rain barrels are often set up so their overflow is directed into rain gardens, which brings us to the main topic here, rain gardens. 

What are rain gardens?

Rain gardens are planted swales designed to capture stormwater from roof gutters, impervious surfaces such as parking lots, or from sloping landscapes. Rain gardens are also called bio-swales. Rain gardens can be small or large and their ideal size depends on how much surface will drain into the rain garden, whether the surface is impervious or not, and also how sandy the soil is. 

Guidelines for sizing rain gardens: Let's look at a 1000 sq. ft. impervious surface where the size of the rain garden is limited to 200 sq. ft. To hold inch or rain, that rain garden should be 5 inches deep (or 1000/200). But here in Florida, we can expect several inches of rain in a severe tropical storm, so that rain garden should be designed to hold three or more inches of rain. If the soil is sandy, the rain will be absorbed quickly. Also, plants with more leaves will soak up more water through transpiration than smaller plants or those with fewer leaves. For more capacity where room to expand rain gardens is limited, dry wells can be added under rain gardens or as an overflow area that is not visible in the landscape.

In general, design the rain garden so that it will drain all of its water in three days or less, so that it does not become habitat for mosquitos. Rain gardens do not generally have mosquito larvae predators such as dragonfly naiads or tadpoles like a pond would.

A large rain garden  

Rain gardens designed to accept rain from parking lots and other large paved areas will need to have the capacity to absorb all of the stormwater. 

Sometimes large rain garden projects are built around existing stormdrains. When this happens, dig out space for the rain garden so that most of the rain can collect below the level of the drain. This way, water will enter the stormdrain only occasionally during severe storm events. If this project includes county or other municipal drain infrastructure, be sure to get the required permits before you start.

Create swales for rain gardens built around overflow drains so the stormwater has a chance to be absorbed BEFORE it reaches the level of the drain.

A small rain garden that was expanded

In 2004, here is the front porch downspout.

In 2008, an expanded downspout rain garden accepts even extended downpours.

The front porch downspout rain garden was one of the first landscaping projects when we moved into the house. Read my "Expanded rain garden" article for how we added a blind drain a few years later to increase its capacity in this restricted landscape area. It also includes link to that first rain garden project article. A few years ago, I eventually dug out and expanded that original dry well, but left the blind drain, which still functions all these years later.

Florida's wet and dry seasons means that we may
receive up to 70% of our rain in only 5 months.

Rain garden plants

Choose native plants that suit the location. If the rain garden is in a swale next to a driveway where people need good visibility to see oncoming traffic, then choose short plants such as bunching grasses, rushes, or sedge, that will not need to be trimmed to stay short. 

However, where possible, use plants with more leaf area such as trees and shrubs to absorb much more water than smaller plants due to their higher transpiration rate. 

Florida's climate, with its wet and dry seasons, limits the choice for rain garden plants because they must be able to withstand both standing water and drought. Here is a short list of recommended rain garden plants for Florida with links to their Florida Native Plant Society plant profiles with more information and a link to native plant vendors that have it in stock. Also, note that good rain garden plants have been tagged as such in this database. In addition, also I've included links to my articles for some of these plants.

Herbaceous Plants

Black-eyed Susan (Rudbeckia hirta)

Blue-eyed grass (Sisyrinchium angustifolium)

Climbing aster (Symphyotrichum carolinianum)

Dotted horsemint or spotted beebalm (Monarda punctata) Dotted Horsemint: an Appreciation

Fakahatchee grass or eastern gama grass (Tripsacum dactyloides)

Meadow beauty (Rhexia spp.)

Meadow garlic (Allium canadense) Chives and meadow garlic

Mistflower or blue mistflower (Conoclinium coelestinum)
Muhly grass (Muhlenbergia capillaris) An Appreciation of Muhly Grass

Netted Chain Fern (Woodwardia areolata) Netted chain ferns
Rain lily (Zephyranthes atamasca)

Starrush Whitetop or white-topped sedge (Rhynchospora colorata) White-Topped Sedge

In addition, there are many other ferns, bunching grasses, rushes, & sedges that work well in rain gardens.

Trees & shrubs

Arrowwood (Viburnum dentatum)
Bald cypress (Taxodium distichum)

Beautyberry (Callicarpa americana) For a more beautiful yard, plant more beautyberry

Cabbage palm (Sabal palmetto)
Dahoon holly (Ilex cassine) & inkberry (Ilex glabra)

Dwarf  palmetto (Sabal minor) & saw palmetto (Serenoa repens)

Elderberry (Sambucus nigra subsp. canadensis)

Wax myrtle (Morella cerifera) Wax myrtle: an under-used Florida native

Sweetbay magnolia (Magnolia virginiana)

Maples (Acer spp.) particularly the red maple (A. rubrum). Florida's red maples.

Salt bush, Groundsel Tree, Sea Myrtle (Baccharis halimifolia)

There are other trees and shrubs that could also work in rain gardens, but it's not usually a good idea to build a new rain garden at the foot of an already established tree, even one that could work in rain gardens. Build new rain gardens far enough away from those trees so that you do not disturb the roots too much.

 

Rain gardens are beautiful!

So after building rain gardens in your own yard, carry it forward and work with your neighbors so that they too can also capture the rain in their yards. Then work with your whole community, to expand the effort beyond your garden gate. The fish and other aquatic animals will appreciate the cleaner water.

Green gardening matters,
Ginny Stibolt