Vegetable raingardens can produce food and reduce stormwater runoff

Abstract

Raingardens are garden beds designed to capture and filter urban stormwater runoff using a permeable soil substrate and plants tolerant of both drought and inundation. The construction of raingardens is actively promoted in many cities, primarily to protect local waterways from the negative impacts of stormwater such as channel erosion and degradation of water quality. To increase the adoption of raingardens by householders, it might be possible to expand raingarden functionality to simultaneously serve as “vegetable raingardens”. Vegetable raingardens would be beneficial in the context of urban agriculture, as they could overcome both space and water scarcity constraints on home vegetable gardening. However, the potential to grow vegetables in raingardens has not been explored and vegetables are significantly different to conventional, hardy raingarden plants. In an 18-month field trial, we assessed vegetable production in purpose-built raingardens. Stormwater was collected from an adjacent rooftop and was applied to the vegetable raingardens through sub-irrigation. One of the vegetable raingardens was lined underneath and the other was unlined, allowing infiltration of excess water to underlying soils. Sub-irrigation was used to limit plant stress and ensure food safety by reducing vegetable contact with potential contaminants present in stormwater. Control gardens were treated with stormwater delivered through overhead spray irrigation, or with potable water delivered by overhead sprays to also examine differences in water source on yield. A range of vegetables were planted including beetroot, onion, spinach, tomato and broad bean. The vegetable raingardens that were tested produced yields generally similar to the control gardens, which represented traditional watering methods for vegetable gardens. The infiltration-type raingarden, sized 7.5% of its catchment area, reduced both the volume and frequency of runoff by >90%. Results indicate that it is possible to both produce adequate yield in raingardens and maintain the function of raingardens in reducing urban runoff, in terms of discharge to waterways.