266 Retractable Shading Reduces Summer Substrate Temperatures in Container-grown Nursery Crops

The influence of no shading; 30%, 47%, or 63% black polypropylene stationary shading; and white poly retractable shading (50% shade operated to provide morning “cold trapping”) on substrate temperature was studied for Coreopsis verticillata `Zagreb' and Forsythia `Lynwood' growing in 2.75-L black polycontainers filled with an unamended Douglas-fir bark substrate. The southwest region of the rootball had the highest daily substrate temperatures under all the shading systems. Substrate temperatures were highest under no shading or 30% shading (often >45 °C) and lowest under retractable shading (never >38 °C). Root death occurred on the southwest portion of the rootball on plants growing under all shading systems except under retractable shading. Coreopsis and Forsythia were taller when grown under 63% stationary shading compared to other shading systems but had more shoot dry weight when grown under retractable shading. Cooler substrate temperatures that prevent damage to the root system may help explain increased growth of some nursery crops when produced under retractable shading.