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Rain Garden Guide

JUNE 16, 2015 | Public Works Department

 

Rain Garden

Information provided from the Kansas State Research and Extension Office and the Environmental Protection Agency. Leavenworth K-State Research and Extension Office, 613 Holiday Plaza; Lansing, KS 66043 (913) 364-5700 can provide additional help with any of the following information.

Kansas City project http://www.lowimpactdevelopment.org/raingarden_design/downloads/10KRG_BrochureKansasCitySm.pdf

https://www.bridgingthegap.org/lawn-garden/rain-gardens/

Hutchinson: http://www.hutchgov.com/egov/docs/1274904364607.htm

 

What is a Rain Garden?

Rain Gardens reduce local stormwater runoff and create a beautiful nature area for you to enjoy. They allow stormwater to soak into the ground instead of going into Leavenworth storm drains. Excess water runoff can also cause erosion, contribute to pollution and flooding. A rain garden should be planted in areas to allow rainwater runoff from areas that don’t drain, such as roofs, driveways, walkways, and compacted lawn areas.

Rain Gardens can be as simple as digging a small depression and planting native grasses or complex as you would like. The goal is to help to pool and slow rainwater. Most lawns do not absorb water as readily as other native plants and require chemical treatments and extra water to look good. Below are some FAQ for your consideration to make your rain garden as effective as possible. Another great resource for Rain Gardening can be found at:  Kansas State University's Rain Garden Project.

 

Q: How do I choose the location of my Rain Garden?

Consider the drainage patterns of the area and how you can most effectively capture and filter the most rainwater before it reaches storm drains.

Install your rain garden...

  • at the end of the roof gutter to capture run off from the roof.
  • along the front walk or driveway to keep runoff from traveling down the sidewalk/driveway and into the storm sewer.
  • in places to minimize the amount of area that you have to mow.
  • In places where runoff can be channeled away from your house to avoid basement flooding problems, preferably 10 feet from the house.
  • in neighborhood common areas where it can most effectively keep runoff from entering the storm sewer.
  • It is better to put the garden in full or partial sun and not under a big tree.
  • A flatter area that will require less digging.

 

Q: How do I build the rain garden?

 (NOTE: Before you start digging call 811 or 1-800-344-7233 to locate any buried utilities.)

 The best time to build a rain garden is in the spring because the plants are more likely to thrive. They can be planted at anytime however, as long as they receive adequate water. Start by laying string around the perimeter of the garden. Dig sloping down towards the edge of the garden farthest from the runoff source, so that edge is the desired depth. While digging the rain garden heap the soil around the 3 edges (not on the one closest to the downspout or runoff) to create a low wall (berm) around the garden that will hold the water during a storm.  Using stakes can help you get the correct depth.  Shape the berm into a smooth very compacted ridge that tapers into the existing lawn area to prevent erosion.   Rocks, bricks or other edging can also be used to create your berm.  You should consider your location and the flow patterns that exist not to negatively impact surrounding areas. 

 

Q: What type of soil do I have for my Rain Garden site?

Clay soils take longer to absorb water, so rain gardens in clay soil must be bigger than rain gardens in sandy or silt soils.  If the soil feels very gritty and coarse, you probably have sandy soil.  If your soil is smooth but not sticky, you have silt soil.  If it is very sticky and clumpy, you probably have clay soil. 

Q: How long and how wide should my Rain Garden be?
The garden typically should be twice as long as it is wide and the length of the garden should be perpendicular to the downspout so the garden catches the most water possible. Runoff should flow out of the downspout and spread evenly across the entire length of the garden. The rain garden must be as level as possible so water doesn't pool at one end and spill over before it has a chance to infiltrate. This should be adapted based on your location and the flow patterns that exist. Think about how your rain garden will catch water.

Q: How big should my Rain Garden be?

You should keep the size reasonable for your yard size and budget. Any water that seeps into the ground instead of running into a storm sewer helps water quality. A rain garden of any size has a positive impact. 

If you want to get technical, (From the EPA Watershed)

  1. You should determine the drainage area, find the area of the house foot print (length x width) then divide it by the number of gutter downspouts you have attached to the house. If the rain garden is to be situated further than 30 feet from the house add in the area of lawn between the house and the garden. 
  2. The next step is to find the infiltration rate.  Dig a hole 8 inches deep and 8 inches wide, fill it with water and let it drain once.  Once it is fully drained, fill it with water again and measure how quickly it drains.  If it drains 3 inches in 6 hours your infiltration rate is 0.5 inches per hour.  Multiply this number by 48 to find your infiltration rate in inches per 48 hour period. (24 inches per 48 hour period, for this example) If it does not drain completely in 48 hours consider another location.
  3. Divide the drainage area by this infiltration rate. This number is the recommended rain garden area to collect the most runoff. This is only a guideline not a rule.

 

Q: How deep should my Rain Garden be?

A typical rain garden is between four and eight inches deep depending on the slope of your lawn.  A rain garden too deep might pool water too long and a garden too shallow will require a larger area to provide enough space. 

If you want to get technical:

  • If the slope of your lawn is less than 4%, it is easiest to build a 3-by-5 inch deep rain garden.
  • If the slope is between 5 and 7%, it is easiest to build one 6-by-7 inches deep.
  • If the slope is between 8 and 12%, it is easiest to build one 8 inches deep.
  • If the slope is greater than 12%, consider another location.

 

Q: What plants should be used?

Choose native plants with long, well established root systems for the garden that will have the most effective absorption and will require the least maintenance. The website www.kswildflower.org is a great resource for Kansas wildflower information, ideas and pictures. 

  • Swamp Milkweed (full to partial sun)
  • Wild Blue Flag Iris (full to partial sun)
  • Hop Sedge (full to partial shade)
  • Great Blue Lobelia (full to partial sun
  • Eastern Purple Coneflower (Echinahea)
  • Black Eyed Susan (full sun)

 

Q: How do I plant and maintain the Rain Garden?

Lay plants out as planned. Space as plant specific instructions indicate. Pack the soil around the plant to remove air pockets.  Apply mulch 2 inches thick over entire bed but avoid burying the plants. 

Mulching will not usually be necessary after the second growing season unless this is the desired look you want. 

Be sure to label the plants so that you can identify them from the weeds as you weed the garden. 

After the native plants are established they should out-compete the weeds and weeding will be less necessary. 

Immediately after planting, water twice a week during periods of low rainfall. As a rule the plants will need one inch of water per week. Once the plants are established you should not have to water your rain garden.