Monday, July 7, 2014

What is a Rain Garden? What Do they Do, and How Can I Plant One?

Rain gardens are planting beds located in areas where rainwater tends to pool as a result of topographic depression, clay rich, or compacted soils.  These gardens are planted with species that love moist to wet soils.   

Why should I build a rain garden?  Why are they so darn special?  Rain gardens function to retain harmful pollutants that would otherwise run off, or percolate down into groundwater.  At the same time, these environmental wonders help to enhance the beauty of your property, and create habitat for birds, butterflies, and other wildlife. In other words--WIN, WIN, WIN.  

Through urbanization, forest and other natural environment is removed and replaced with roads, buildings, etc.  When this happens, we disrupt natural drainage patterns by covering litter and soil that once absorbed water with impervious surface, or area that does not absorb rainwater.  

Rain gardens work to fill the gap, and provide stormwater filtering functions that are otherwise lost.

If you want to plant a rain garden on your property, how do you know where to put it?  It's pretty simple--wait for it to rain and observe the natural drainage patterns on your property.  If you see water pooling in certain areas, you can assume that area is potentially suitable for a rain garden.

Once you have a site in mind there are a few additional things to look for:
  • Tree Roots – Keep your rain garden away from tree root zones, using the tree’s canopy as your boundary
  • Structures – Keep your rain garden at least 10 feet from your home or any other structure on your property
  • Underground Lines – Before you break ground for any reason, call Miss Utility of Virginia to mark the buried lines on your property (1-800-552-7001)
  • SoilYou will want to test the soil at your proposed site for proper drainage
  • Check out the Virginia Beach map with soil survey data below to get an idea of the types of soil you have on your property
  • ElevationThe proposed site you are considering from your rain garden should be below the areas you wish to drain, or “treat.”  Additionally, the natural topography should direct rain toward your proposed site  
The last couple things you need to figure out are the size (surface cover), and depth of your rain garden. The size of your rain garden depends on two things: soil type, and the amount of surface area you will be draining.

In general, sites with greater amounts of impervious ground cover and slower-draining clay soils will require a larger rain gardens.  Sites with more pervious ground cover, and sandy, well-drained soil can get away with smaller gardens. 

You can use the Rainscape calculator to estimate the square footage of your rain garden, using the drainage

The depth of your rain garden is dependent on the drainage of the site.  You need to test how fast water drains in the area you wish to build your rain garden (percolation test).  To do this, dig a hole six inches wide and 18 inches deep.  Fill the hole with water, and observe how long it takes for the water to infiltrate the soil.  If the water has not drained in 48 – 72 hours, you will need to amend your soil or choose another location for your garden.

If your soil passed the percolation test, you only need to excavate six inches for water to pool and an additional three inches for mulch.  If your soil did not pass the drainage test, you must dig a deeper rain garden.  It should be as deep as possible, not to exceed three feet. (This is in addition to the six inches for ponding and the three inches for mulch.)  Fill the hole with a blend of 50% sand, 25% leaf compost, and 25% clay free topsoil.  The excavated pit should be flat, not bowl-shaped, so it will hold more water.

If you are curious about the type of soil existing on your property take a look at the Virginia Beach map, with soil survey data at

In order to overlay the soil survey data:

  • Click the OFF button under the environmental tab on the left hand side to turn it ON
  • Click the + directly under the button that now says ON to show all environmental data
  • Zoom in on the map until the x symbol beside the soils checkbox diapers
  • Click the checkbox next to soils, and soils data will be overlaid onto the map
  • You may now zoom into the property you want to look at and click on the area of interest
  • If it is easier for you, you may at this point search by address by clicking the magnifying glass icon in the top left   
  • On the left hand side click the + next to soil type and then again next to each of the soil types to get a description. 
      If you have determined that your site is appropriate for a rain garden, we recommend having a professional perform the installation. 

      You can find recommended plants here.

      Find further information and the Lynnhaven River Now Rain Garden publication here
      Now.... bring on the rain!
       Compiled by Clint Boaz, Intern; Edited by Trista Imrich, Pearl Homes Coordinator, LRNow

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