Designing Your Rain Garden

Below are some general tips to help you design your own rain garden. These are fairly simple to follow, but if you have questions, help is close by! We will be happy to visit your site and provide technical assistance. If you want to delve into the technical aspects of designing a rain garden, check out on our Links and Resources Page and some example designs at the bottom of this page.

Sizing the Garden

To establish the size of your rain garden, calculate the square footage of the area that will drain to the location of your garden and divide by three.

For rain gardens attached to downspouts, there are two additional steps. For example, take a 1,000 square-foot roof with two downspouts, one of which is connected to your rain garden.

Step 1: Divide the roof square footage (1,000) by the number of downspouts (2).

Step 2: Multiply the result in step 1 (in this case, 500) by the number of downspouts connected to your rain garden (1) and then divide by three to determine the square footage of your garden. In this example, the resulting garden would be 167 square feet in size (500 times 1 divided by 3). Of course, the square footage doesn’t have to be exact.

If your soil is extremely compacted or clayey, increase (even double) the size of your garden, or amend the soil with compost.

Determining the Depth

To figure out what depth your garden should be, test the infiltration rate of the soil – that is, how fast water soaks into the ground. This is simple. Dig a hole about 12 inches deep and fill it with water. After 24 hours, measure how much water has soaked in to the ground. For example, if half of the water has soaked into the ground, you would dig your garden so that it is 6 inches deep at the deepest part. If your soil drains very slowly, you may need to amend it with compost.

Determining Shape

Rain gardens can take on just about any shape you want them to. The shape in part will be dictated by the location. Remember to keep the garden at least 10 feet away from the house, and avoid placing it over septic system drainage fields and underground utilities. The rest is just up to your imagination.

Example Designs

Maplewood, MN Designs – Check out Maplewood, Minnesota’s web site which has design examples for several different types of gardens.

Design Tips