|Vegetative Growth||Ensure photosynthetic growth is not limiting|
|Bulb Formation||To maintain leaf growth|
|Bulb Fill||Less critical, but to maintain growth and prolong bulking|
See more on Onion Growth Stages.
Applications of iron, such as foliar or fertigation, can be used to increase early leaf production and crop productivity.
Generally, onions appear insensitive to iron deficiency, with most soils supplying adequate levels of iron to meet crop needs. Under extreme deficiencies, leaves become completely chlorotic and bleached.