A high tunnel environment was evaluated for production of leaf (`Two Star') and romaine (`Parris Island Cos') lettuce (Lactuca sativa) in a northern location (lat. 64°49'N). Ten plantings were made 1 week apart from May to August. Averaged over the season, the air temperature was 1.5 °C and the soil 0.8 °C higher in the high tunnel than the field. `Two Star' planted on 3 Aug. and harvested on 16 Sept. produced higher yield (P < 0.001) in the tunnel. Head weight was 195 ± 12 g in the tunnel and 99 ± 8 g in the field. For the 13 July-planted `Two Star' lettuce, the field produced significantly (P < 0.001) more at 202 ± 21 g/head than the 135 ± 29 g/head in the tunnel. The three consecutive field plantings of 1, 8, and 15 June resulted in higher `Parris Island Cos' yields than corresponding plantings in the high tunnel. Head weights for harvests on 11, 18, and 25 July were 457 ± 60, 476 ± 65, and 478 ± 25 g under field conditions and 354 ± 46, 331 ± 52, and 312 ± 14 g in the high tunnel. `Two Star' was observed less prone to bolting than `Parris Island Cos'. Although a high tunnel did not generally support increased productivity in this study, the added protection resulted in high quality lettuce with limited necessary preparation and marketing loss in comparison to the field-grown lettuce.
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