Organic Onion Grower Manual
The common dry yellow onion belongs to the Amaryllidaceae (Amaryllis family). Allium Cepa is related to a great number of other species of similar odor and taste — garlic, leek, chive, welsh onion. The shallot is considered a form of A. cepa. Asia is considered the centre of origin — Northwestern India, Afghanistan, parts of the USSR and China. Onions are sensitive to photoperiod. Long days are favorable to onion production as this enhances leaf development and formation which, in turn, is directly related to bulb size. Early varieties require 13 hours for bulb initiation while late varieties require 16 hours for bulb initiation. Onions begin to form bulbs when day length reaches the appropriate duration for the cultivar, providing temperatures are high enough. Early seeding or transplanting is therefore essential. Cool weather during early growth of the plant promotes formation of seed stalks (bolting).The onion bulbs quicker in warm than at cool temperatures.