Northern Rhode Island Conservation District

 

 

How To Plant A Rain Garden

REASONS TO PLANT A RAIN GARDEN:

  • Protect your drinking water from pollutants.
  • Clean nearby rivers and lakes for healthy swimming and fishing.
  • Plant a garden with purpose and beauty.
  • Create a garden of native plants.
  • Create a small wildlife habitat near your home.
  • Use a practical solution to a common problem.

JOIN EFFORTS FOR CLEANER
RHODE ISLAND WATERS


 A RAIN GARDEN IS DIFFERENT FROM OTHER GARDENS

  • They are planted beside parking lots, driveways and roofs to intercept rainwater running off these watertight surfaces.
  • They prevent pollutants from entering storm drains and nearby waters.
  • They are planted with native plants that survive without extra fertilizers and insecticides that can pollute local waters.


CHOOSE YOUR RAIN GARDEN SITE

  1. First, decide if the rain garden will filter stormwater flowing from a roof, or a parking lot or a fertilized lawn.
  2. If the roof, parking lot, or lawn is larger than 3000 square feet, then more than one rain garden may be needed to handle the rainfall coming from this larger area.
  3. Watch this area during a rainstorm. Water will collect and flow downhill. Watch the direction that it takes. This may be your  garden site. You can also choose a nearby site and redirect the flow of water by digging the soil or even adding underground pipes.
  4. Choose a garden site that is at least ten feet away from building foundations and from your septic system. This prevents rainwater from leaking into these areas.


HOW LARGE SHOULD THE GARDEN BE?

  1. The size will depend on your budget and the space you have available. A larger garden will trap and filter larger amounts of  stormwater runoff, however, a garden that is less than 300 square feet is effective while being easier to dig and plant.
  2. Ideally, the length of the garden should be twice as long as the width. See the example below of a 200 square foot garden.

If your goal is to control 100% of the stormwater runoff you can calculate the garden size based on the surface area of the stormwater runoff area. For instructions, go to Rain Gardens: A How-To Manual for Homeowners.You can also choose your own size. A Rain Garden that filters some of the runoff is better than no Rain Garden at all.


IS SOIL REPLACEMENT NEEDED?

  1. The soil should allow rainwater to drain through at about 1 inch per hour. Sandy soils are best for drainage.
  2. The soil also needs to provide adequate nutrients for the plants. You can choose native plants that grow well in the type of soil you already have.
  3. If you are not satisfied with the soil at your site, you can also replace the soil with a mixture of 50-60% sand, 20-30% compost, 20-30% topsoil.
  4. For some simple soil tests you can go to go to the web site Rain Gardens: A How-To Manual for Homeowners.


DIGGING THE RAIN GARDEN

  1. Before you start digging, call Dig Safe (1-888-DIG-SAFE or 344-7233) to check for underground utilities in your chosen garden site.
  2. Mark the borders of your garden edge.
  3. Loosen all the soil in the garden to a depth of about 2.5 feet. Some people use shovels, some use backhoes.
  4. If you hit bedrock, consider changing the garden site because the rain water will not drain well.
  5. Dig an inlet or shallow trench that directs the flow of rain water into the garden from the parking area, roof, or lawn.
  6. Your Rain Garden will be shaped like a basin with the lowest point in the center. Here the water will collect and drain down through the soil.
  7. A Rain Garden is typically 4"-8" deep at the center. You can choose your own depth or you can calculate a depth based on the slope of the garden. For instructions, go to the web site Rain Gardens: A How-To Manual for Homeowners.
  8. The edges of the garden should be higher so the stormwater will stay in the garden and drain down through the soil.
  9. The following method can be used to help you measure garden depth from edge to center.
  10. Place a stake on one edge of the garden and another stake in the center. Tie a string to the garden edge stake at the ground  level. Tie the other end to the garden center stake. Use a carpenter level to make the string level with the garden edge.
  11. Dig the garden so it gradually gets deeper with the center the deepest point. Again, you are making a basin shape.
  12. Measure the center stake, from the string to the soil. Keep digging until you reach your chosen depth.


 

 

CHOOSING THE NATIVE PLANTS

Following a rain storm, a large amount of water will be directed toward the Rain Garden. Most of the stormwater runoff will go to the  lowest point in the center. Plants must be able to tolerate these soaking conditions. On the other hand, these same plants will need to  grow well during the dry conditions between rainstorms. There are a variety of native plants that can survive despite these changes. See the list of Rhode Island native plants that can be used in Rain Gardens by going to URI web site for Healthy Landscapes.

You can choose trees, shrubs, vines, grasses and herbaceous plants with a wide variety of flower and berry colors,  plant heights and blooming times so each gardener can plan their own unique garden design.

Here are some of the plants we have used in demonstration Rain Gardens in Pawtucket and Woonsocket. All these  plants can tolerate both wet and dry conditions to some degree, however, some tolerate soaking conditions better than others. You can think of this when you choose plants that will grow in the middle vs. the edges of your garden.  The middle, being the lowest area, will receive most of the stormwater runoff.

  • Plants that usually grow in wetlands but occasionally in non-wetlands
    Vernonia noveboracensis (New York Ironweed)
    Cornus amomum (Silky Dogwood)
    Spiraea tomentosa (Steeplebush)
     Eupatorium maculatum (Joe-pye weed)
     
  • Plants that are found in wetlands but less often than the plants listed above
    Lindera benzoin (Spicebush)
    Aster novae-angliae (New England Aster)
     
  • Plants that grow in both wetlands and non-wetlands
    Solidago rugosa (Rough goldenrod)
    Panicum virgatum (Switchgrass)


MAINTAINING THE RAIN GARDEN

 

While the plants are young, you may need to water and weed occasionally. Once plants have grown larger and stronger they will tolerate dry periods better and will shade out any  weeds.

The picture at right is of a Rain Garden several months after planting. This particular garden has not needed extra watering at this point, but it has needed some weeding.

For detailed information on individual species of native plants, go to the Plant Database.


LOOKING FOR MORE INFORMATION?

Research on Rain Garden effectiveness
Haddam Research/Demonstration Garden
CLICK HERE

Planting a Rain Garden
University of Rhode Island's "Healthy Landscapes"
CLICK HERE

High School students plant a demonstration Rain Garden
Northern Rhode Island Conservation District
CLICK HERE

Protecting local water using several practical techniques
R.I. Department of Environmental Management
Urban Environmental Design Manual
Chapter 1
Chapter 2
Chapter 3

New England nurseries that sell native plants
New England Wetland Plants
413-548-8000
CLICK HERE

New England Wildflower Society
508-877-7630
CLICK HERE

 

 

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