Editing Onion (section)

=== Cultivation ===

[[File:Onion mother plants (bulbs) for production seeds.jpg|thumb|Onion bulbs to be planted for seed production]]

[[File:Field with onions.jpg|thumb|Large-scale onion cultivation]]

Onions are best cultivated in fertile, well-drained soils. Sandy loams are good as they are low in sulphur, while clayey soils usually have a high sulphur content and produce pungent bulbs. Onions require a high level of [[Soil#Nutrients|nutrients]] in the soil. [[Phosphorus]] is often present in sufficient quantities, but may be applied before planting because of its low level of availability in cold soils. [[Nitrogen]] and [[potash]] can be applied at regular intervals during the growing season, the last application of nitrogen being at least four weeks before harvesting.<ref>{{cite web |url=http://www.caes.uga.edu/publications/pubDetail.cfm?pk_id=7749 |title=2007 Onion Production Guide |editor-last=Boyhan |editor-first=George E. |editor-last2=Kelley |editor-first2=W. Terry |year=2007 |website=Production Guides |publisher=University of Georgia: College of Agricultural and Environmental Sciences |access-date=2013-09-14 |archive-date=11 October 2013 |archive-url=https://web.archive.org/web/20131011180348/http://www.caes.uga.edu/Publications/pubDetail.cfm?pk_id=7749 |url-status=live }}</ref>

Bulbing onions are day-length sensitive; their bulbs begin growing only after the number of daylight hours has surpassed some minimal quantity. Most traditional European onions are referred to as "long-day" onions, producing bulbs only after 14 hours or more of daylight occurs. Southern European and North African varieties are often known as "intermediate-day" types, requiring only 12–13 hours of daylight to stimulate bulb formation. "Short-day" onions, which have been developed in more recent times, are planted in mild-winter areas in the autumn and form bulbs in the early spring and require only 11–12 hours of daylight to stimulate bulb formation.<ref>{{cite web |url=http://extension.oregonstate.edu/gardening/onion-bulb-formation-strongly-linked-day-length |title=Onion bulb formation is strongly linked with day length |last=Savonen |first=Carol |date=2006-07-13 |publisher=Oregon State University Extension Service |access-date=2013-09-14 |archive-date=9 November 2013 |archive-url=https://web.archive.org/web/20131109131226/http://extension.oregonstate.edu/gardening/onion-bulb-formation-strongly-linked-day-length |url-status=live }}</ref> Onions are a cool-weather crop and can be grown in [[Hardiness zone|USDA zones]] 3&nbsp;to&nbsp;9.<ref name=almanac /> Hot temperatures or other stressful conditions cause them to "[[Bolting (horticulture)|bolt]]", meaning that a flower stem begins to grow.<ref>{{cite web |url=http://www.gardeningknowhow.com/edible/vegetables/onion/onion-bolting.htm |title=What is Onion Bolting and how to Keep an Onion from Bolting |last=Rhoades |first=Jackie |website=Gardening Know How |date=17 August 2010 |access-date=2013-03-27 |archive-date=1 May 2013 |archive-url=https://web.archive.org/web/20130501001809/http://www.gardeningknowhow.com/edible/vegetables/onion/onion-bolting.htm |url-status=live }}</ref>

Onions are grown from seeds or from partially grown [[bulb|bulbs called "sets"]] or [[starter bulb]]s. Onion seeds are short-lived and fresh seeds germinate more effectively when sown in shallow rows, or "drills," with each drill 12" to 18" apart.<ref name=almanac>{{cite web |url=http://www.almanac.com/plant/onions |title=Onions: Planting, Growing and Harvesting Onion Plants |website=The Old Farmer's Almanac |access-date=2013-03-27 |archive-date=5 November 2012 |archive-url=https://web.archive.org/web/20121105125106/http://www.almanac.com/plant/onions |url-status=live }}</ref><ref>{{cite web |url=http://www.ars.usda.gov/Aboutus/docs.htm?docid=6463 |title=Onion production |date=2011-02-23 |publisher=USDA: Agricultural Research Service |access-date=2013-03-27 |archive-date=11 April 2014 |archive-url=https://web.archive.org/web/20140411135334/http://www.ars.usda.gov/Aboutus/docs.htm?docid=6463 |url-status=live }}</ref> In suitable climates, certain cultivars can be sown in late summer and autumn to overwinter in the ground and produce early crops the following year.<ref name=RHS/>

Onion bulbs are produced by sowing seeds in a dense pattern in early summer, then harvested in the autumn when the bulbs are still small, followed by drying and storage. These bulbs are planted the following spring and grow into mature bulbs later in the growing season.<ref name=PFAF>{{PFAF |access-date=2013-03-22}}</ref> Certain cultivars used for growing and storing bulbs may not have as good storage characteristics as those grown directly from seed.<ref name=RHS>{{cite book |title=The Royal Horticultural Society Encyclopedia of Gardening |editor-last=Brickell |editor-first=Christopher |year=1992 |publisher=Dorling Kindersley |isbn=978-0-86318-979-1 |page=345}}</ref>

Routine care during the growing season involves keeping the rows free of competing weeds, especially when the plants are young. The plants are shallow-rooted and do not need much water when established. Bulbing usually takes place after 12 to 18 weeks. The bulbs can be gathered when needed to eat fresh, but if stored, they are harvested after the leaves have died back naturally. In dry weather, they may be left on the surface of the soil for a few days for drying, then are placed in nets, roped into strings, or laid in layers in shallow boxes to be stored in a cool, well-ventilated place.<ref name=RHS />