Day-neutral Strawberry Season Extension Using Low-tunnel Organic Production Systems

Guest Authors: Steve Poppe and Esther Jordan, University of Minnesota West Central Research and Outreach Center (WCROC), Morris, MN, Emily Hoover, Emily Tepe, Andy Petran and Jack Tillman, U of M, Dept. of Horticultural Science, St. Paul.

Availability of locally grown strawberries is extremely limited in the Upper Midwest, primarily due to the short growing season. Fruit is an important part of a healthy diet, and while there is an expressed interest in having greater access to locally grown strawberries, lack of suitable varieties and production systems has prohibited growers from being able to fulfill this need in our region.

For the last two years, our main objective was to conduct day-neutral strawberry trials using a low tunnel organic production system. To make fresh, locally grown strawberries available for an extended season, we established six day-neutral strawberry cultivars in raised beds using plasticulture with and without tunnels. We harvested day-neutral strawberry fruit from mid-July through mid-October 2013/2014 at the West Central Research and Outreach Center (WCROC) Morris site, the University of Minnesota St Paul campus site, and two farmer-cooperator sites.

A second objective was to work with current and potential growers to educate them on these new strawberry production methods. The third objective was to evaluate our success at increasing strawberry production in the Upper Midwest through collaboration with partner organizations. If successful, this new method of growing long-season strawberries may help increase the number of strawberry growers in the Upper Midwest, increase yields and therefore availability of locally grown strawberries from June through October.

Low tunnel organic strawberry production systems used by the University of Minnesota research team.

Figure 1: Low tunnel organic strawberry production systems used by the University of Minnesota research team.

Traditional June-bearing strawberry varieties in Minnesota have a baseline yield of 5,500 pounds/A. Preliminary data from USDA low tunnel trials calculated yield for day-neutral varieties varying between 9 632 - 21 280kg/ha (8 600 - 19 000 lb/ac) (Lewers, 2012). Average 2013-2014 yield under low tunnels was 19 174 kg/ha (17,120 lb/ac) at the St. Paul site and 24 398 kg/ha (21 784 lb/ac) at the WCROC site; both within the USDA benchmark and exceeding June-bearing strawberry varieties in Minnesota.

In order to determine individual size of fruit (g) of each cultivar, we randomly chose 20 berries per treatment at each harvest in 2013 and 2014. At WCROC, the average berry weight (g) across six cultivars for both years under the low tunnel was 16.45g, while the non-low tunnel averaged 15.22g. At St. Paul, the average berry weight (g) across six cultivars for both years under the low tunnel was 12.98g, while the non-low tunnel averaged 12.42g. By comparison, 2010-2011 data from the WCROC June-bearing variety trial shows the average berry weight was 11.45g per individual fruit. After two years of research, the six day-neutral cultivars are proving to have larger individual fruit size when compared to June-bearing strawberry trials in Minnesota.

During the 2013 late summer/fall picking season at the WCROC site, we tasted a noticeably sweet strawberry. We randomly took brix/sugar levels during the picking season of all six cultivars in the low tunnel and non-low tunnel treatments. The results showed an average brix level of 7.6 between late July and early October in both low and non-low tunnel treatments. To compare these brix levels, we also randomly took readings in our 2013 WCROC June bearing variety trial between late June and early July; the results showed an average brix level of 7.7. This comparison shows that day-neutral cultivars are just as sweet as June-bearing cultivars commonly grown in Minnesota.

For step-by-step instructions on constructing a low tunnel system for strawberry use, or for more information on the project, please visit our low tunnel strawberry blog at the UMN Commercial Fruit website, We will continue with this research project 2015-2016. Steve Poppe can be contacted at

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