All about bioswales

What's a bioswale?

A shallow ditch with gently sloping sides and various layers of soils beneath.


A bioswale - sometimes called a vegetated ditch - slows stormwater runoff and directs it to an area where it can soak in. It achieves the same goal as a rain garden, but is usually designed to manage a larger amount of runoff. A bioswale often uses grass and plants to stabilize the soil, reduce erosion, slow the flow, and absorb runoff.

What are the benefits?

Bioswales help filter out harmful pollutants like oil, fertilizer, pesticides, soap, and animal waste so they don't find their way into the storm system and our streams.

They reduce flooding by capturing the rainwater that would otherwise pool up on ground surfaces.

Grassy bioswale

Bioswale (JPG)

How should you care for a bioswale?


Bioswales only serve their purpose if you take care of them properly. You can view a complete list of maintenance components for your bioswale, but here are the top five:

  • Grass.

    Keep the bioswale's grass thick and healthy and mowed to three or four inches. Don't leave grass clippings in the bioswale.

  • Sunlight.

    If your bioswale shows bare spots in its grass, it might not be getting enough sunlight. You may need to do some pruning and tree trimming to let the sunlight through.

  • Standing water.

    Your bioswale should drain freely between storms. Standing water can kill the bioswale's grass and other plants.

  • Water flow.

    Keep the water flowing evenly over the entire width of the bioswale.

  • Pollution.

    Keep trash and other contaminants like oil, gas, and paint far away from the bioswale.