Research trials were conducted at Agricultural Research Institute, Mingora Swat over two consecutive growing seasons from November to June 2013-14 and 2014-15. In the first trial seedlings of 45, 60 and 75 days old were transplanted on 5 different dates (30th November, 15th December, 30th December, 15th January and 30th January) to study its effect on premature bolting in onion. Transplanting dates and seedling age exerted significant effect on different growth and yield parameters studied. Plant height, number of leaves at bolting, stem thickness, days to maturity, bulb diameter, bulb weight and total yield (ton ha-1) decreased with delay in transplanting as well as with increasing seedling age. On the other hand, bolting and cull percentage decreased with delay in transplanting and increased with increase in seedling age. Maximum marketable yield (ton ha-1) was recorded when 60 days old seedlings were transplanted on 15th December. The correlation co-efficient analysis data revealed a positive correlation between marketable yield (0.671 ton/ha) and bulb diameter (0.381). Non- significant positive correlations of marketable yield were recorded with bulb weight (0.173), number of leaves at bolting (0.097), stem thickness (0.091) and plant height (0.106). The association of marketable yield with bolting percentage (-0.381) and % cull (-0.552) was significantly negative. In the second trial three commercial cultivars ‘Swat-1’, ‘Saryab Red’ and ‘Chiltan-89’ were transplanted on five different dates at 15 days interval (25th November, 10th December, 25th December, 10th January and 25th January). Cultivars varied in their susceptibility to bolting. Cultivar Swat-1 took significantly maximum (78.67 days) to bolting initiation and recorded minimum bolting percentage (12.51%) compared to ‘Saryab Red’(13.75%) and ‘Chiltan-89’ (17.32%). Early transplanting took less (108.06 days) to bolting initiation. Bolting percentage was maximum (34.52%) at early transplanting and reduced with delay in transplanting from 25th November to 25th December. Bolting was not recorded at late, (10th and 25th January) transplanting irrespective of the cultivar. When compared to ‘Saryab Red’ and ‘Chiltan-89’, ‘Swat-1’ had maximum plant height (65.58 cm), number of leaves per plant (10.64), stem thickness (15.43mm), bulb diameter (60.08 cm), bulb weight (169.08 g), and days to maturity (168.37), total (32.94 vii ton ha-1 ) and marketable yield (25.07 ton ha-1 ). Plant height (61.24cm), number of leaves per plant (10.96), stem thickness (17.24 cm), bulb diameter (63.08 cm), bulb weight (149.31g), and days to maturity (167.89), total yield (31.07 ton ha-1) was maximum at early transplanting and decreased with delay in transplanting. Cultivar Swat-1 produced maximum marketable yield (25.07 ton ha-1) than ‘Saryab Red’ and ‘Chiltan-89’. Marketable yield was maximum at mid transplanting date (25th December); attributed to less bolting and percent cull compared to early transplanting. Unmarketable yield at early transplanting was largely due to bolting while at late transplanting it was due to small ungraded bulbs. In the third trial different rates of nitrogen fertilizer (75, 100, 125 and 150 kg ha-1) were applied at different transplanting dates (15th Nov, 1st Dec, 15th Dec, 1st Jan and 15th Jan) with the objective to determine its influence on inflorescence development in onion bulb crop. Bolting percentage decreased gradually with increase in the rate of nitrogen fertilizer. Maximum bolting percentage was recorded in early transplanting and declined with delay in transplanting. Bolting incidence did not occurre in very late (15th January) transplanting irrespective of the rate of nitrogen applied. Plant height, stem thickness, bulb diameter, bulb weight and total yield ton ha-1 increased with increase in nitrogen fertilizer and conversely showed a downward trend with delay in transplanting. Different rates of nitrogen fertilizer didn’t significantly influence number of leaves plant-1. However, early transplanting exhibited significantly more leaves than late transplanting. Early transplanting took maximum 175.88 days to maturity than late transplanting (163.75) days. Maturity was delayed with increase in nitrogen fertilizer. Percent cull decreased with increase in the rate of nitrogen fertilizer. Marketable yield ton ha-1 was maximum at mid transplanting date (15th December) and with maximum rate of nitrogen fertilizer. The correlation co-efficient analysis revealed that marketable yield ton ha-1 has positive correlation with plant height, number of leaves plant-1, bulb diameter, bulb weight, total yield ton ha-1 and negative correlation with stem thickness bolting percentage and percent cull. Bolting percentage has positive association with percent cull. It can be concluded that bolting resistant cultivar is not available in this country, however, ‘Swat-1’ performed best in the existing cultivars. Research should be initiated to develop bolting resistant cultivars or produce resistance in available cultivars through phenotypic recurrent selection. Modification in cultural practices remained the viable option for the growers to mitigate bolting problem. Transplanting should be delayed in such a way to avoid plants receiving cold temperature at sensitive stage to minimize bolting. Correct transplant age (50-60 days) and ample nitrogen fertilizer of 125-150 Kg ha-1 also reduced the incidence of bolting