Rain Gardens

Rain Gardens

Homeowners should consider creating “rain gardens” because they can significantly reduce  water issues.  When rain pours down heavily it often results in flooding and wet basements. The use of gardens to capture some of the excess water can make a big difference, especially if many residents within a community are willing to create them.

The purpose of a rain garden is to keep as much rain water as possible on site thus reducing street flooding and the overflow of storm drains. Rain gardens will collect storm water runoff from impervious surfaces such as streets, roofs, driveways, parking lots and sidewalks.  Another huge benefit is that these gardens will reduce pollution and erosion in nearby streams, such as the Potomac River and the Chesapeake Bay. A rain garden absorbs 30% more water than a lawn of the same size and they filter runoff and pollutants through the soil and plants.

Yes, a rain garden is functional but it can also be a beautiful addition to your outdoor space. Picture it as a concave shape with a ponding depth of around 6-12 inches.   The creation of this depressed area allows a drain for excess rain water and a planting area that is both aesthetically pleasing and low in maintenance.  Creating a swale, a rock filled ditch, or an underground perforated pipe surrounded by small rocks or large pebbles (also called a French drain), will control the flow of water.


First, during and after a rain go outside and observe the path of the rain water.  Where is the water moving, especially water from downspouts, roofs, roads, and driveways? The slope near the foundation should be moving the water away from the house.


Select an area with good drainage that is free from large tree roots or utilities and is at least 10 feet away from the foundation. First, it is necessary to do a penetration test to ensure that the potential site drains. Using a post hole digger, dig a hole about 2 feet deep and fill it with water from your garden hose. Once that drains, fill the hole again with water and make sure it drains within 48 hours. If it does not drain, you will need to select another site. A second option is to remove one foot of the clay under the depressed area where you want to situate the rain garden and replace it with a soil mix of two-parts large sand, one-part topsoil (no clay), and one-part compost.


Lay out the shape of your rain garden using a hose or a long rope. Then start digging and use the excess soil to either build up the sides of the swale or to regrade levels in the garden. Splash rocks are needed to hold the soil in place near the downspouts or swales where the water enters the rain garden. Sides of the garden should be gradually sloped. Plants suited to a rain garden are those that can tolerate both excess moisture and also dry periods. A blend of native ferns, grasses, perennials, shrubs, and even a few small trees (depending on the size of the rain garden) would be ideal. After planting, water the plants well and add a leaf mulch to keep weeds down and build the soil. The garden must be watered frequently until it is established. At that point, it should not need watering or fertilizing.


Some favorite plants to use in a rain garden are:

Ferns:

Cinnamon fern (Osmunda cinnamomea), tolerates shade, gets around 4 feet tall

Sensitive fern (Osmunda regalis), tolerates shade, gets around 4 feet tall

Perennials:

Sweet flag (Acorus americanus), likes wet feet so plant at base of rain garden, grows 2-3 feet tall

Swamp milkweed (Asclepias incarnata), likes sun and grow around 3-4 feet

New York aster (Aster novi-belgii), likes sin, grow 1-3 feet tall

Joe-pye weed (Eupatorium dubium)

New York ironweed (Vernonia noveboracensis), likes sun and grows 2-4 feet tall

Grasses:

Switch grass (Panicum virgatum)

Tussock sedge (Carex stricta)

Shrubs:

Black chokeberry (Aronia melanocarpa)

Buttonbush (Cephalanthus occidentalis)

Sweet pepperbush (Clethra alnifolia)

Red osier dogwood (Cornus sericea)

Winterberry (Ilex verticillata)

Spicebush (Lindera benzoin)

Arrowwood (Viburnum dentatum)

Trees:

Sweet bay magnolia (Magnolia virginiana)

River birch (Betula nigra)


Create a rain garden. They add beauty while also providing essential habitat and food for pollinators, birds, and beneficial insects.  Keeping rain water on site helps to recharge the ground water while also allowing the water to be cleaned by the soil and the plants. A rain garden will not be a habitat for mosquitoes because it is not a site with standing water. Many counties offer rebates to encourage the installation of rain gardens so be sure to check with your local government to see what is available.