Southern highbush Blueberry production in High Tunnels: Temperatures, development, yield, and fruit quality during the establishment years

Abstract

Growers interested in producing early, high-quality, southern highbush blueberries (Vaccinium corymbosum L.) in high tunnels face a lack of information regarding appropriate cultural methods. We sought to elucidate the optimal date to close high tunnels to hasten vegetative and reproductive growth of organic southern highbush blueberry cultivars Emerald and Jewel grown in Georgia. The three dates selected to close the high tunnels were 15 Dec., 2 Jan., and 16 Jan. High tunnels raised soil and daytime air temperatures during winter months, but the tunnels did not retain heat at night and did not provide freeze protection without the use of propane heaters. The high tunnel microclimate advanced both vegetative and reproductive growth compared with outdoor plants. Averaged over the 2-year study, the 15 Dec. tunnel closure advanced flower initiation by 38 days for 'Emerald' and 39 days for 'Jewel' compared with outdoor control plants. Synchronization of flowering of the two cultivars was poor in 2007 when 'Emerald' flowered much earlier than 'Jewel' and much better in 2008. In 2007, flower and fruit development of 'Jewel' were faster than that of 'Emerald' with Jewel going from the appearance of individual flowers to ripe fruit in 80 days as compared with 105 days for 'Emerald'. Total yield was strongly correlated with fruit set (r = 0.94). 'Emerald' fruit contained higher concentrations of soluble solids and anthocyanins than 'Jewel' fruit, and anthocyanin concentrations increased throughout the harvest period. No fruit matured in 2008 as a result of freeze damage. The biggest obstacle for high tunnel production of southern highbush blueberries appears to be preventing freeze damage and assuring pollination. Cost-effective freeze protection and ways to promote good fruit set will be critical to successful production of early southern highbush blueberries in high tunnels.