Runoff Landscaping for Parking Lots

bioswale parkingThere are many advantages of introducing smart landscaping into a parking lot, including minimizing flooding, maintaining cleanliness, and creating green space. Smart landscaping means creatively and effectively implementing a landscape project that meets the needs of a parking lot while incorporating environmental efficiencies.

The most important function of parking lot landscaping is to provide natural drainage, a water collection network, and stormwater filtration. Landscaping can enhance the aesthetic quality of the space and help reduce temperatures in the summer by providing shade. It’s necessary to be mindful of the type of tree to use in a parking lot, as it should not drip sap on cars or have fruit that is too big or heavy.

Bioretention is an efficient technique to catch and treat parking lot runoff. Landscape islands are best when installed below the parking lot level so they can collect water as it runs down and off.

Usually, bioretention landscape elements are filled with a sandy, compost-rich soil mix, topped with a layer of mulch and a dense vegetative cover. That way, stormwater is absorbed into the soil, where it gets filtered and absorbed into the groundwater.  The water is cleaned by the soil’s microbial action.

To avoid flooding during heavy storms, bioretention areas incorporate a ‘pond’ about 6 to 8 inches deep with an overflow outlet to drain the water. For a bioretention area to be effective, it should cover 5% of the entire paved surface.


It is important to consider that even small lots can be designed with a variation of this technique by using perimeter bioswales, which are depressions along the perimeter designed to remove silt and pollution from surface runoff water, distribute the water away from some locations toward a larger collection system, and minimize flooding. Parking lots should be designed so that water is directed toward the perimeter. Bioswales are effective landscaping techniques that can be incorporated into many types of vegetation.

Rain Gardens and Designed Wetlands

Rain gardens, deep perimeter strips, and designed wetlands are other types of bioretention landscape elements that receive excess runoff that bioswales cannot support. They are the final elements in the stormwater runoff network system.