What is a long-day type onion variety?

Question: 

When leafing through a garden catalog, an onion variety was described as a long-day type. What is meant by the term long-day?

Answer: 

Onion bulb formation begins when a certain day length is reached.  Short-day onion varieties begin to form bulbs when they receive 10 to 12 hours of daylight, intermediate-day onions need 12 to 14 hours of daylight, and long-day varieties require 14 or more hours of daylight.

Bulb size is largely determined by the number and size of the leaves at bulb initiation.  The larger the tops (foliage area) at bulb initiation, the larger the bulbs will be.  (The size of onion bulbs also depends on weather, soil conditions, and other factors.) 

Long-day onion varieties are the best choice for gardeners in Iowa and other states in the upper midwest.  Short-day varieties generally produce small bulbs when grown in northern areas because of the small amount of foliage present at bulb initiation.  Long-day varieties, however, are able to produce large tops before bulb initiation occurs.  As a result, long-day onion varieties typically produce the biggest bulbs. 
 

Tags: 

Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Horticulture and Home Pest News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on . The information contained within may not be the most current and accurate depending on when it is accessed.