On the surface a rain garden has the same wild flowers and other native plants you'd expect to see in any garden. However, the construction design and strategic placement of vegetation of rain garden aid in the capture of rain water runoff from impervious surfaces, such as roofs and streets and serve as a means to filter the water into the ground, rather than running off to a storm drain.
Watch the video below to see how This Old House suggests going about excavating and building a beautiful rain garden.
Although rain garden size is not critical--its inefficiency will depend on knowing several factors including: your current landscape, soil type and measured garden depth.
First, size your rain garden to fit your landscape. Sometimes you only have so much space you can devote to the garden or you can only dig so deep into your yard due to utilities, roots, rocks or other obstructions. If you are not limited by space, a good guide may be an 8’ X 10’ area to drain one downspout from a typical house.
Second, size your rain garden to fit your soils. Feel the soil for sand, silt or clay. The composition of the native (existing) soils will determine the infiltration rate of water in the soil. Although most rain gardens are 4 to 8 inches deep, you should determine your infiltration rate so that the garden drains within 24 hours, which is less time than mosquito larvae need to mature. You can determine how quickly the soil will drain within a 24 hour period by by doing a standard soil test and conducting a simple soil percolation test.
Third, size your rain garden to fit your runoff. Most of the water in the rain garden will come from your roof through your downspouts.
Step 1. Assess the Site: Determine the Location, Size and Depth
I. Location
- Locate your rain garden on a downhill 10-20 feet away from the house, near a downspout to prevent water from seeping into your foundation.
- DO NOT place over or near the drain field of a septic system.
- DO NOT place where water stands in your lawn. This shows low permeability of the soils and will not accept the rain garden infiltration.
- DO NOT place within existing drainage ways such as swales and ditches.
- DO NOT install under large trees.
- Best if placed in sunny or partly sunny locations , but shade gardens are possible.
- DO check with your local building department before installing your rain garden as some of the installation requirements may conflict with local ordinances or zoning regulations.
II. Sizing your Garden
Although rain garden size is not critical--its inefficiency will depend on knowing several factors including: your current landscape, soil type and measured garden depth.
First, size your rain garden to fit your landscape. Sometimes you only have so much space you can devote to the garden or you can only dig so deep into your yard due to utilities, roots, rocks or other obstructions. If you are not limited by space, a good guide may be an 8’ X 10’ area to drain one downspout from a typical house.
Second, size your rain garden to fit your soils. Feel the soil for sand, silt or clay. The composition of the native (existing) soils will determine the infiltration rate of water in the soil. Although most rain gardens are 4 to 8 inches deep, you should determine your infiltration rate so that the garden drains within 24 hours, which is less time than mosquito larvae need to mature. You can determine how quickly the soil will drain within a 24 hour period by by doing a standard soil test and conducting a simple soil percolation test.
Third, size your rain garden to fit your runoff. Most of the water in the rain garden will come from your roof through your downspouts.
*Please refer to the TLCRGI Homeowner’s Manual for more information about sizing your rain garden, including more diagrams, calculations and worksheets.
Step 2:Planning and Designing your Garden
- Draw a map of the property to scale
- Determine how big you want your garden to be:
- Call Ohio Utilities Protection Service (OUPS) “Call Before You Dig” at 1-800-362-2764
- Choose plant selection and design the layout of your rain garden: Pick plants that are appropriate for your soil, moisture level, and sun exposure.
- Plan how water will be directed to the garden
- Devise an overflow plan
Step 3: Build your Garden
Some commonly used materials and tools include:- Rope or String
- Garden hose
- Shovel & pick
- Ruler, sock or wood scrap
- Pencil or marker
- Compost, sand or gravel
- Moisture‐loving native plants
- Shredded hard wood mulch
- Decorative rock
- Wheelbarrow
