PS 33-155 - Season extension in urban agriculture: Low tunnel, double tunnel, and ground cover assessment for Red Russian kale winter production

Background/Question/Methods

Extended season farming using high and low tunnels is one way farmers are meeting demand for locally grown produce in times of low supply (i.e., winter, early spring) because they can create a more favorable microclimate for plant growth. Ground covers, such as straw and plastic mulch, also can be used in conjunction with tunnels and may improve the microclimate and production. These tools can be particularly useful for urban farmers to maximize production on smaller plots. In this project, we examined whether 1) a double tunnel (low tunnels within a high tunnel) and 2) low tunnels, in conjunction with bare ground, straw mulch, or plastic mulch, influenced air and soil temperature around kale plants and ultimately increased crop yield and nutrients. We grew kale during one winter season in low tunnels on 10 urban farms across the District of Columbia, Maryland, and Virginia and in a double tunnel at the University of the District of Columbia’s Agricultural Experiment Station (Maryland).

Results/Conclusions

In comparison to production solely within a high tunnel (i.e., no low tunnel), the double tunnel increased crop yield, reduced the duration of freezing air temperatures, and increased the duration of time air temperatures exceeded the base threshold for plant growth (10 °C), regardless of which ground cover was used. Additionally, soil temperature was higher in double tunnels with straw and plastic mulch than double tunnels or a single tunnel with no soil cover. However, fiber was lower in kale grown in double tunnels compared to the high tunnel alone. In the 10 urban farms, yield of kale was low in all combinations of low tunnels and ground covers. Our results suggest that low tunnels are not effective for growing kale during cold winters, but double tunnels can increase output and could help meet winter demand for local and nutritious produce.