Develop a Design

Even if you choose one of the standard designs that our gifted gardeners have donated, every garden on earth is site specific. The rain garden you have in mind may be a different size or shape than the design provided, or you may want take things out, add things, or design your own. No matter what you choose to do, you must adapt your garden to the local conditions of your site.

Regarding size

You can’t have a rain garden that is too large.  However, any size garden will make a difference, even a small one.  The ideal situation is to create a garden that will absorb all the rain that would otherwise flow away from your yard. To calculate the most useful size of a smaller garden, here’s how:

  • Figure out what kind of soil you have.
  • Estimate the area from which your garden will get rain. Multiply width times length of your rooftoop, to get square feet. Add the square feet of paved areas. Remember, though, that different parts of your roof drain to different downspouts—you want to estimate only the square footage that will drain into your rain garden. Don’t forget roof overhangs.
  • For sandy soil, your rain garden should be 20-30% of the drain area. For example, if your roof and driveway measures 1200 square feet and all the rain from them will be used, your rain garden should be 20 to 30% of that, or 240-360 square feet.  (ex: 10’ X 24’)
  • For clay soil, your rain garden should be about 60% of the drain area (Clay absorbs water very poorly; the varieties of rain garden plants that do well in clay take at least three years to get established. Soil replacement may be the best choice in clay soils).
  • If you improve your soil drainage and replace your soil with rain garden mix (50-60% sand, 20-30% topsoil, 20-30% compost), your rain garden should generally be about 20-30% of the square footage of your drain area.

Rain gardens for single-family homes will typically range from 150 to 400 square feet. But remember; any size rain garden, even a small one, will contribute to solving local water pollution problems. It will also be a lovely addition to your landscape.

Now you are ready to prepare your site.