Winter Season Greenhouse Production of Strawberry in Desert Southwest

Ninety percent of all strawberry fruit grown in the US is produced in coastal California, between the months of March and November. Due to limited production regions suitable for strawberry field production in winter, the total supply during the months of November, December and January is relatively low compared with other months. That allows a potentially valuable winter market season for local greenhouse production, a season which includes major holidays, not only to fill diminished supply but to provide high-quality, high flavor strawberries without concern for the shelf-life necessary for nation-wide distribution. Winter season greenhouse strawberry production is practiced widely in Asian countries and in Northern Europe, but very minimally in the US. Very little documentation exists for methodology and practice of greenhouse strawberry production, and the development of such information is necessarily limited to the regional climates in which it is generated as regional responses will be different. We have spent the last several years developing production systems and identifying important factors affecting growth and productivity in the unique semi-arid climate of the desert southwest.  As a part of this study, we examined planting systems and planting density. Two standard field production cultivars, ‘Albion’ and ‘Portola’ were planted at densities of 8 and 12 plants m^-2 in 11-liter strawberry buckets and at 8 plants m^-2 in continuous Styrofoam troughs in substrate consisting of 1 peat: 1 coco coir: 2 perlite and irrigated using standard Yamazaki nutrient solution with pH adjusted to result in a drainage pH of 5.5 – 6.5. Plants were planted, in a greenhouse covered with a single layer of F-Clean (ETFE) greenhouse glazing film with light diffusing characteristics and high UV transmission, in August 2013 and initial harvesting began in October. As of mid-February 2014 cumulative yield for ‘Albion’ at 8 plants m^-2 in buckets, 12 plants m^-2 in buckets and 8 plants m^-2 in Styrofoam trough was (mean±SE) 5.0±0.4, 6.2±0.7 and 6.2±0.3 kg m^-2 respectively. Cumulative yield for ‘Portola’ for the same period and planting systems/densities was 7.3±0.5, 9.1±0.3 and 8.7±0.4 kg m^-2 respectively. Brix (TSS) was 8.6±0.15 and 6.0±0.08 and total acidity was 11.0±0.07 and 8.9±0.12 g/L citric acid equivalent for ‘Albion’ and ‘Portola’ respectively. While yields are acceptable, additional management techniques to improve fruit quality characteristics must be developed, and existing cultivars bred specifically to produce fruit with high flavor characteristics in greenhouse need to be introduced.