Abstract

Onion are the third most important vegetable crop sold in South Africa. Optimum sowing dates for new cultivars was determined in Bloemfontein (South Africa) during 2009 and 2010. Cultivars planted in 2009 and 2010 were ‘Charlize’, ‘Jaquar’, ‘Python’, (South Wester, 2009; Ceres Gold, 2010). Unavailability of ‘South Wester’ seed resulted in replacement with ‘Ceres Gold’. In 2009 onion seeds were sown on 30 April, 7 and 21 May and in 2010 on 11, 25 May and 8 June. Trials were laid out as a randomized complete block design with each treatment combination replicated 3 times. Plant height and leaf number were measured 18 weeks after emergence. At harvest, bulb yield and quality were recorded. Cultivars differed with respect to growth habit, bulb size, neck diameter and bolting, but not bulb fresh mass and yield. Sowing date did not influence plant height and leaf number significantly, except in 2010 where the early sowing dates resulted in taller plants. The respective delayed sowing dates in 2010 (11 May, 25 May, 8 June) significantly decreased average bulb fresh mass (71.48, 49.42, 49.21 g bulb^-1) and yield (40.96, 34.05, 28.20 t ha^-1). In both seasons thinner necks were recorded for later planting dates.  Cultivars tested in Bloemfontein can be sown from late April to late May, although the best results were obtained from sowing in May.

Key words: Bolting, bulb diameter, bulb neck diameter, bulb shape, bulb yield, leaf number, photoperiod, plant height, temperature.