The way in which crop processors can influence the timing of a crop's harvest is by the choice of cultivar and planting date. However, the crop duration (time between planting and harvest) is substantially affected by the weather. Processors' records illustrate the magnitude of these effects. The mean crop duration for the sweet corn cultivar NK51036 was 111 days for the 1980/81 to 1984/85 seasons in the Manawatu, but the range was 38 days. The practical problem facing the processor is how to allow for these effects when planning optimal use of factory plant and labour.