Stormwater planters are a lot like rain gardens. They are landscape features designed to capture runoff and filter out sediment and pollutants. So, what exactly is a stormwater planter?
A stormwater planter is a small, contained vegetated area that collects and treats stormwater using bioretention. Bioretention systems collect and filter stormwater through layers of mulch, soil and plant root systems, where pollutants such as bacteria, nitrogen, phosphorus, heavy metals, oil and grease are retained, degraded and absorbed. They have been described as “rain gardens in a box”. Aside from their water management functions they provide excellent aesthetic and biodiversity benefits.
The stormwater is treated the infiltrated
Treated stormwater is infiltrated into the ground as groundwater (infiltration planter) or, if infiltration is not appropriate, discharged into a traditional stormwater drainage system (flow-through planter). Stormwater planters do not require a large amount of space and can add aesthetic appeal to parking lots, and commercial and residential properties. Stormwater planters typically contain native, hydrophilic flowers, grasses, shrubs, and trees.
There are many benefits of creating a stormwater planter, such as:
- A form of bioretention but differs from rain gardens in that they are above ground systems.
- Reduces stormwater runoff volume and flow rate.
- Improves aesthetic appeal of streets and homes.
- Provides shade to nearby buildings to reduce energy costs.
- Contributing roof area and desired drain time determines size and specifications.
- Crushed rock or a geotextile fabric is recommended between the soil and gravel layers to prevent soil from mixing with the drain rock.
- Planters should be placed at or above grade and ideally alongside buildings to capture rainwater runoff.
- Use of impermeable liner is recommended when adjacent to structures, near property lines, on erodible slopes, and areas with high water tables.
There are variety of things you can do to ensure the longevity and success of your stormwater planter; here are some tips:
- Regular inspection of structural components, especially after large rain events.
- Periodic cleaning of inflow and outflow points.
- Removal of sediment and debris to ensure proper drainage.
- Routine maintenance of soil media.
- Removal of invasive species or noxious weeds by hand, or other mechanical methods, before they flower.
- Replacement of dead or diseased plants as needed.
- Water in times of drought.
There are a variety of plants that are suitable for stormwater planters, but native plants fit the bill in a unique way. Selecting wild, native plants provides options that are adapted to the region, requiring less special care. Plants must be suitable for seasonally moist and dry soil conditions. Avoid permanent irrigation if possible.
Native aquatic and riparian plants thrive in moist conditions and often have broad root systems, useful for filtering the water. In addition, such specimens provide habitat and food for native birds and animals. These plants are as appealing as ornamental species but increase biodiversity and native flora. Select plants with matching cultural requirements and those that require minimal upkeep.
Charles River Watershed Association. (September 2008). Stormwater Planter. Retrieved from https://nacto.org/docs/usdg/stormwater_planter_crwa.pdf.
Oregon State University Extension Service. (July 2018). Stormwater Planter Factsheet. Retrieved from https://catalog.extension.oregonstate.edu/sites/catalog/files/project/pdf/em9213.pdf.
Southeast Metro Stormwater Authority. Stormwater Planters Factsheet. Retrieved from https://www.semswa.org/wp-content/uploads/2021/05/Stormwater_Planters_Fact_Sheet.pdf