New, Free UHI Guide to Woody Shrubs for Stormwater Retention

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Harrison Street bioswale in Syracuse by Ethan Dropkin

New from the Cornell Urban Horticulture Institute (UHI) is Woody Shrubs for Stormwater Retention Practices (Northeast and Mid-Atlantic Regions), a free 56-page guide by Ethan Dropkin and Nina Bassuk. The Guide includes an extensive suggested plant list with beautiful photos and helpful illustrations. It will be of interest to anyone working with vegetated filter strips, bioswales, rain gardens, specialized tree pits, and stormwater planters.

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Successful bioswale at Cornell Plantations. Photo by Ethan Dropkin

A portion of the information is based on a three-month study in Ithaca, NY conducted by Horticulture Masters of Professional Studies student Ethan M. Dropkin under the guidance of UHI Director Nina Bassuk. The study focused on testing the flood and drought tolerances of six shrub species, all included in the guide. The species (Amorpha fruticosa, Hippophae rhamnoides, Salix arenaria, Salix purpurea, Shepherdia argentea, and Spiraea tomentosa) showed tolerance of both long-term flooding AND drought which makes them good candidates for use in stormwater retention/infiltration plantings. They and the other shrubs in the Guide are also tolerant of other urban stresses.

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Spirea tomentosa was one of the shrubs studied in Ithaca by Ethan Dropkin; photo by Ethan Dropkin.

From the Introduction:

“Planted stormwater retention and infiltration practices are important for reducing runoff and maximizing green space in urban areas. While a wide variety of herbaceous plants are often successfully used in these spaces … they can present maintenance issues because of the need to annually cut back dead foliage and stems. Utilizing woody plants decreases the need for additional seasonal maintenance while successfully adding aesthetic and functional vegetation to stormwater retention practices.

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Hypericum kalmianum flower, Courtesy Cornell Woody Plants Database

Key Concept:

“When selecting plants for stormwater infiltration, common sense would seem to dictate the use of wetland plants. However, due to the rate at which most of these practices allow water to infiltrate, the majority of planted stormwater practices will likely only be inundated for a few minutes after a small storm event, and up to a day or two for a larger event. Unlike most permanent or semi-permanent wetlands, these areas remain relatively dry most of the time. Because of this characteristic, plants that can handle both temporary inundation and relatively protracted drought are the best choices for a low-maintenance planting.

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Cornus ammomum fruit by Ethan Dropkin

The Guide includes a checklist for site assessment and guidance on design and maintenance considerations.

The free Guide to Woody Shrubs for Stormwater Retention is available here.

 

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