Vidalia Onion Production Guide

Onions are among the most widely adapted vegetable crops, as they can be grown from the tropics to subarctic regions. This adaptation is primarily due to differing responses to day length. Unlike most other species, day length influences bulbing in onions as opposed to flowering. Onions are grouped into three groups based on their response to hours of daylight. The short-day varieties bulb with daylengths of 10–13 hr; intermediate varieties bulb with day lengths of 13–14 hr and are found in the mid-temperate regions of this country. Finally, long-day onions are adapted to the most northern climes of the United States as well as Canada, and they bulb with daylengths greater than 14 hr.