Onions (Allium cepa) are a cool-season biennial crop typically grown as an annual. Dry bulb onions are harvested after the leaves have died back and the bulbs have fully matured. Green bunching onions are harvested while the leaves are still green and before the bulbs have developed. The terms 'scallion' and 'spring onion' are sometimes incorrectly used interchangeably for green onions. Scallions are onions that completely lack bulb formation, while spring onions have bulbs somewhat more developed than green onions.