Winter greenhouse strawberry production using conditioned plug plants

Two- to three-week-old 'Sweet Charlie' strawberry (Fragaria xananassa Duch.) plug plants were conditioned [seven 9-hour short days without chilling (21 degrees C day/21 degrees C night) followed by seven 9-hour short days with chilling during the nyctoperiod (21 degrees C/12 degrees C night)] in September, then planted in a vertical hydroponic system for winter greenhouse production. Conditioned plugs produced significantly more fruit than did nonconditioned control plugs in January and February, but the difference was nonsignificant in March and April. Fruit yield increased linearly with height in the column (approximate to 40 g/plant for every 30-cm increase in column height), probably because of increasing light level. When productivity is considered on an area basis (kg.m(-2)) and the column height effect on yield is accounted for, productivity over a 4.5-month period was 4.8 kg.m(-2) for controls and 7.8 kg.m(-2) for conditioned plugs. Conditioned plug plants offer the potential for increasing strawberry productivity and therefore the profitability of a winter greenhouse production system.