Rain gardens have been introduced into the horticulture physie as a way of reducing stormwater runoff which has become an increasing problem due to urban growth. But what else can rain gardens do for the environment?
- Traps stormwater runoff.
- Creates a filter for stormwater runoff befor it reaches the local streams.
- Reduces flooding and drainage problems.
- Helps increase the ground water supply.
- Decreases the need to cut grass.
- Adds to the beauty of the yard and the neighborhood.
- Increases biodiversity by encouraging birds and butterflies to enter the yard.
DIY Rain Gardens
Please note that properly built rain gardens will not attract mosquitos. The concept of a rain garden is that water is quickly absorbed into the ground. This normally will occur in several hours and even under heavy rains will only take 24 hours to infiltrate the ground. Mosquitoes need stagnant water and at least a week to complete the life cycle. So a well maintained rain garden will not create that type of environment.
Where to put your rain garden
Rain gardens need to be placed in strategic locations where runoff is occurring or where runoff can be directed to such as from a roof gutter. An example of how much water can be diverted can be demonstrated by a small home 30’x50′. This house covers 1,500 square feet and if the roof on this house receives 1-inch of rain that equates out to 935 gallons of water that will become runoff. So the next time it rains, grab an umbrella, go outside, and observe the land and where the water is going.
Things to keep in mind when picking location
- Do not put the rain garden in an area that stays wet. This observation means that the soil is too heavy or there exists slow percolation.
- Plan a rain garden 10′ or more away from the home. If needed 4-inch PVC or black plastic drain pipe can be used to direct water from down spout.
- Pick an an area that is mostly flat or gently sloping.
- Plan where the runoff will enter and where it will overflow in the event of a severe storm.
- The amount of sun is important so look for locations with full or partial sun. Do not plan a rain garden under an established tree. The construction of the rain garden can damage the roots and eventually kill the tree.
Once the site has been chosen a preliminary test needs to be done of the area. This can be done by following these simple steps.
- Dig a hole 8″x8″ and fill with water. Wait 24 hours to see if the water has percolated through the soil. If it has fill up with water again and mark with a tooth pick. Wait 24 hours again and then go out and measure how far the water has gone down, If the water has not gone down dig deeper and do the test again. Do not go deeper than 18 inches. This measurement is the depth of percolation. Soil that has percolation problems will need to be amended with organic material and some sand or a new location will have to be chosen.
Size of Rain Garden
Once the location has been tested for water percolation the next step is to calculate the size. This is simply done by following the equation below.
- Length x width of house=square foot
- Take square foot/number of down spouts=the square feet of the garden.
- Example 20′ x 60’=1200 square feet then
- 1200/4=300 square feet this equals a garden size 10′ x 30′
Depth was calculated during the soil perculation test when the hole was filled with water twice. See things to keep in mind when picking location.
Designing Rain Garden
This is done on graph paper. Plant height and sun requirements need to be considered along with individual style such as natural or refined. Also where the entrance ( where the water will enter) and where the berm is (where overflow will go). This is important because it helps control runoff during heavy rains.
Part of your design plan should include a bird bath or bird house. This will help attract wildlife to the garden.
Picking the Plants
A rain garden works better when native plants are used. These plants have deep roots that help with percolation and once established require little maintenance. But keep in mind plants from the local region do better than the same plant from a different state.
To get additional information about native plants talk with nursery personnel, read books and/or contact the local extension office or land grant college.
How to Prepare the Rain Garden Bed
Before the rain garden is dug spray paint or lay a garden hose out to outline the design. If the rain garden will be built in an area where grass is the grass will have to be killed with a herbicide or covered with black plastic. The sod will then have to be dug or cut with a sod cutter.
After the sod has been removed dig a level depression the depth of filtration. This was calculated in section called Depth. If the soil is compacted or filtration depth is deeper than 10 inches the garden will need to be tilled to a depth of 1 foot and compost added.
Please note that soil removed can be used to create the berm.
How to Plant the Garden
Once the rain garden is dug planting can begin. If shrubs or trees are used dig a hole twice as wide as the root ball and twice as deep. Then gently remove from container and place in hole. Fill hole in keeping the crown of the plant level with the existing grade from the container. Then firmly tap soil and place a plant marker.
If planting grasses, ferns, or wildflowers only use plugs. These plugs while more expensive are easier to plant and to adapt to the rain garden. Remember to label these too.
Next place border around the rain garden with the entrance and berm open. Place 3-inches of double shredded mulch in rain garden. This is very important for weed control and the double shredded mulch will not float away.
Rain gardens can beautify a yard and neighborhood, bring more wildlife into the area, and help individuals reduce runoff from hardscape while being expensive ($2-$5 a square foot). But the cost and time is worth it.