After you have determined where to place your rain garden, there are still other factors that need to be considered in the planning and construction of your garden, such as the size and depth.


The size of your rain garden depends upon the drainage area you are focusing on and soil types on your property.

The drainage area (shown right) that will be flowing into your rain garden is the total area of impervious surfaces on your property that will be contributing storm water to your rain garden during a rainfall event, such as a rooftop, driveway, patio, or other surfaces that water cannot penetrate. The more surfaces you have contributing to your total drainage area, the larger your rain garden should be, depending upon what kind of soils are present in your yard.

In general, 50 square feet to 150 square feet is sufficient for the area of a rain garden. However, if you find that you want to create a rain garden that is over 300 square feet in area, it is best to actually split that garden into two smaller gardens, as it is easier to maintain that way.


DRAINAGE AREAS. Red areas represent the drainage area of the property shown above. Arrows represent the flow of storm water during a rain event.


The depth of your rain garden is dependent upon three things:

  1. the size of your drainage area and amount of water that will be flowing into your garden
  2. the types of soils present in the place that you live
  3. the area of your rain garden

The size of a drainage area varies per property, since it is dependent upon the amount of impermeable surfaces contributing rainwater to a rain garden in one’s yard. However, soil types across Long Island generally do not vary significantly. Most soils on Long Island consist of sand or loam (a mix of sand, silt, and a small portion of clay) which are both considered to support good rates of water infiltration.

Since Long Island soils allow for quicker infiltration, rain gardens here need to be within 6-12 inches deep depending upon how big you plan on making your rain garden.

To test how well the soil in your yard allows water to infiltrate, you can perform an infiltration test.

Infiltration Tests

Performing an infiltration test will help you determine where the best place is for you to plant a rain garden. Find out more by clikcing  on the the button below.

How To Conduct an Infiltration Test

Just For Fun

You can use the USDA Web Soil Survey application linked below to find out what  soil types are present in your area on Long Island.

USDA Web Soil Survey

Extra Help

Want more help figuring out how to plan out your garden?
Try out the Three Rivers Rain Garden Alliance rain garden size calculator.

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