High Tunnel Primocane Fruiting Raspberry Production in a Cold Region (USDA Zone 3b) of the Upper Midwest

Northern Minnesota has short growing seasons (109 days at Grand Rapids, MN) that put most primocane fruiting raspberries at risk for freezing damage.  High tunnels have the potential to extend the season by several weeks in the spring and fall which could benefit fall bearing raspberries.  The objective of this study was to compare productivity of fall bearing raspberry cultivars in high tunnels with that in the field under USDA Zone 3b conditions.  Bear root plants of five cultivars of primocane fruiting raspberries (Autumn Bliss, Autumn Britten, Caroline, Joan J, and Polana) were planted in a 21X48 ft high tunnel and in the field at 2x5 ft spacing using a randomized complete block design on May 8 and May 14, 2008 respectively. A propane heater was used for frost protection in the high tunnel for both years of the study.  In 2008, 154 lb of berries were harvested from the high tunnel and 0.5 lb total from the field planting.  The field season was terminated on Oct 8, while the high tunnel season ended on Nov 6, four weeks after the field season. Previous year’s canes were removed to the ground on March 12, 2009.  In 2009, all cultivars except for Polana grew to a height of 6-6.5 ft.   A two layer trellis system was used in the high tunnel to keep the canes from falling over.  Total of 379 lb of berries (equivalent of 16,000 lb/acre) were harvested from August 5 to Nov 2 in the high tunnel, compared with only 80 lb of berries harvested from August 12 to Oct 5 in the field. For the five cultivars tested, Polana was the earliest, followed by Autumn Bliss, Autumn Britten, Joan J, and then Caroline.  Although Caroline was the latest of the five cultivars tested, it was the most productive.  Autumn Bliss was the least productive, while Polana, Autumn Britten, and Joan J were intermediate.  Soil and leaf nutrient analyses showed that all nutrients were within sufficient ranges. The major pest was spider mites in the high tunnel, and was controlled well with predatory mites in 2009.  The winter of 2008/2009 was cold with outside air temperatures of -40°C in mid January, but all cultivars sprouted out well with minor or no winter damage in the high tunnel in 2009. In conclusion, by using high tunnels, primocane fruiting raspberries can be successfully grown and profitable in northern Minnesota.