Levels of bacterial soft rot in stored onion bulbs were affected by rates and application times of nitrogen (N) fertiliser, time of lifting, and water during the field‐curing period. Bulbs of onions given 240 kg N/ha (double the local recommended rate) had more rots during storage than onions that received no N or 120 kg N/ha. Onions that received N late in the growing season had more storage rots than onions that received N early in the season, or were not supplied with N. There were no noticeable differences in levels of rots in onions that were lifted at 50–70% top‐down or at >90% top‐down in each of the treatments. When N treatments were compared, the percentage of storage rots was higher in onions that were given supplementary water during field‐curing than in non‐irrigated onions. To reduce the incidence of storage rots it is recommended that onions are not over‐fertilised with N, and crops are lifted at >90% top‐down. Bulbs should be moved under cover and dried before storage if wet weather is expected during field‐curing.