Common globe onion is the best known of this aromatic tribe. Spring onions are any variety of onion that is pulled when just beginning to bulb. Tree onion forms a basal bulb, while the flowers are replaced by a cluster of small bulbils that weigh the stalk to the ground, allowing the bulbils to take root. Potato onion forms a large cluster of plump smallish onions at the base. Shallots (eschallots or scallions) form an above ground bulb that splits to form a cluster of bulbs with a delicate flavour. Chinese onion is an Asian species cultivated for its crisp textured bulbs, which are popularly used raw, pickled or cooked. Nodding onion is a North American perennial with an intense onion flavour. Canada onion forms crisp white bulbs and has deliciously onion-scented foliage. Milder flavoured leeks originate from the Mediterranean. Garlic leek is perennial and develops a large basal bulb, which splits into several cloves. Poor man’s leek grows in the same manner as leeks, but has hollow leaves. The plant divides at the base, forming a perennial clump. Ramps form scallion like onion and garlic tasting bulbs.
Onions requires a well tilled and weed free soil, good drainage and a sunny position. Plant onions by seed. In areas with a short growing season, grow them to the size of bulbils or sets, in their first season, then plant them out to mature in the second season. Regular weeding is essential and do not over water. Harvest globe onions at any stage. When onions have stopped growing, the tops fall over and wither. Choose a sunny day to pick onions and store in a dry, well ventilated area to prevent fungal rot.
information sourced from The Complete Book of Herbs