Matanuska-Susitna Borough

Rain Gardens

DK Rain Garden 6.14 sm

Rain gardens are vegetated areas built specifically to manage stormwater runoff from driveways, sidewalks, roofs, and other paved surfaces.

Rain gardens slow down stormwater runoff from pavement and rooftops to prevent flooding and erosion.

Rain gardens give stormwater runoff an area to spread for removal of sediment and pollutants.

Rain gardens soak in stormwater runoff to recharge groundwater and wells.

Build a Rain Garden

These steps are a quick guide to building a rain garden.

  1. Determine a location for your rain garden. Identify a spot for your rain garden by watching stormwater flows on your property. Think about how runoff will enter your rain garden.
  2. Determine the size and shape of your rain garden. A rough guide to determine the size of your rain garden is to estimate the square footage of runoff input from roofs and driveways. Your rain garden size should be 10% of this number. For example, if you have a roof and driveway area of 2,000 sq. ft, your rain garden should be 200 sq. ft. The rain garden can be any shape you like. It is handy to outline your rain garden location with spray paint.
  3. Dig approximately 2-3 feet deep. You can do this yourself, or hire a contractor. Be sure to avoid utility lines and tree roots. Try to stay ten feet away from your foundation.
  4. Place an amended soil mixture of half sand-half topsoil into the hole you just dug. This mixture can be purchased pre-mixed. If you have compost, you can also add that to the fill. Leave about 6 inches of space below the surface of your rain garden to have room for mulch and stormwater runoff ponding. If your soil has high clay content, you can place a layer of gravel and sand underneath the amended soil to improve filtration.
  5. Select native, perennial plants that can withstand wet and sunny conditions for your rain garden. See the Mat-Su rain garden plants for ideas. Friends and neighbors can be a great help with planting! Remember to water your plants immediately after you put them into your garden.
  6. Spread a 2-3 inch layer of mulch over your rain garden. You could also use gravel instead of mulch. The mulch will help keep out weeds and adds another filtration layer. There should still be 4-6 inches of ponding room in your rain garden. Be sure to water the garden immediately after planting, and regularly during the first summer.
  7. Water plants immediately after planting, and then twice a week while they are establishing themselves in your rain garden. Once the rain garden is established, provide regular weeding and pruning care as you would other gardens. You can add annuals to your rain garden if desired for additional color and variety.
  8. For more information and consultation about rain gardens, contact us at This email address is being protected from spambots. You need JavaScript enabled to view it..

Rain Garden Examples

FAQ

How much does a rain garden cost?

Costs of a rain garden vary based on size and how much the landowner can accomplish themselves. The most expensive cost is usually excavation. Other costs include plants, mulch, and soil.

Where can I get assistance installing my rain garden?

We can assist homeowners with their rain garden design. We may be able to assist schools, commercial properties, and public spaces with rain garden installation. For school projects, we have ideas for incorporating rain gardens into the curriculum. Contact us at  This email address is being protected from spambots. You need JavaScript enabled to view it..

Where should I put my rain garden?

It helps to watch where water flows after a hard rainfall. Place your rain garden at least ten feet away from your foundation and near a source of runoff. Avoid septic tanks and trees. Full or partial sun areas are best. Some common rain garden locations are at the base of gutter downspouts, a low and gently sloping area of the lawn, and areas that catch runoff from pavement.

How will my rain garden work in winter?

Rain gardens can still infiltrate some water during winter. Rain gardens will work to catch snowmelt. Recommended rain garden plants are hardy, native, perennial plants that will survive harsh winter weather.

What kind of maintenance will my rain garden require?

Regularly water your rain garden the first summer of installation. Some weeding may also be necessary over time in your garden. Rain gardens with native perennial plants should not require much maintenance once they are established.

Will my rain garden or rain barrel attract mosquitoes?

No. Rain gardens are dry most of the time. Rain gardens puddle water during storm events, and soak the water into the ground in the hours following a storm event. Rain barrels are usually fitted with covers and screens to keep out mosquitoes. You can also add things to the water, such as vegetable oil or Mosquito Dunks to keep any prevent any larvae from hatching.

Techniques

Stormwater management techniques are also called low impact development or green infrastructure. These techniques use plants and bioengineered landscape features to manage stormwater runoff on-site, filter out debris and pollutants, protect salmon habitat, and keep drinking water clean.

Green roofs provide a vegetative cover instead of an impervious surface. Vegetation absorbs runoff that can pollute waterways and cause problems with flooding and erosion. Green roof ideas.

Porous paving lets water infiltrate into the ground. This is unlike regular pavement that blocks any stormwater from being absorbed.

Rain chains are a beautiful alternative to gutter downspouts that can freeze or become clogged. They can be used to direct water to rain gardens or rain barrels. Rain chain ideas.

Rain barrels collect rain water to reuse for gardens and other household water tasks. Rain barrels reduce the amount of runoff from roofs and the water demand placed on wells. Rain barrel ideas.

Vegetated shorelines reduce erosion, keep debris and pollutants out of water bodies, provide salmon habitat, and reduce property maintenance. This is true for both rivers and lakes! Shoreline guidelines

Further Resources

 

Rain Garden Documents

Rain Garden Plant List
Download
Berms, Water Flow Ideas
Download
Green Roof Ideas
Download
Initial Site Evaluation Form
Download
Rain Barrel Ideas
Download
Rain Chain Ideas
Download
Rain Gardens: A How-To Manual for Homeowners in Anchorage
Off-Site Link
Alaska Low Impact Development for Homeowners
Off-Site Link