Editing Onion (section)

== Producing onions ==

=== 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 />

=== Pests and diseases ===

Onions suffer from several pests and diseases. The most serious for the home gardener are likely to be the [[onion fly]], stem and bulb eelworm, white rot, and neck rot. Diseases affecting the foliage include rust and smut, downy mildew, and white tip disease. The bulbs may be affected by splitting, white rot, and neck rot. Shanking is a condition in which the central leaves turn yellow and the inner part of the bulb collapses into an unpleasant-smelling slime. Most of these disorders are best treated by removing and burning affected plants.<ref name=Hessayon>{{cite book |title=Be your own Vegetable Doctor |last=Hessayon |first=D.G. |author-link=D. G. Hessayon |year=1978 |publisher=[[Pan Britannica Industries]] |isbn=978-0-903505-08-6 |pages=22–23}}</ref> The larvae of the onion leaf miner or leek moth (''[[Acrolepiopsis assectella]]'') sometimes attack the foliage and may burrow down into the bulb.<ref>{{cite journal |last=Landry |first=Jean-François |s2cid=86748199 |year=2007 |title=Taxonomic review of the leek moth genus ''Acrolepiopsis'' (Lepidoptera: Acrolepiidae) in North America |journal=The Canadian Entomologist |volume=139 |issue=3 |pages=319–353 |doi=10.4039/n06-098}}</ref>

The onion fly (''Delia antiqua'') lays eggs on the leaves and stems and on the ground close to onion, shallot, leek, and garlic plants. The fly is attracted to the crop by the smell of damaged tissue and is liable to occur after thinning. Plants grown from sets are less prone to attack. The larvae tunnel into the bulbs and the foliage wilts and turns yellow. The bulbs are disfigured and rot, especially in wet weather. Control measures may include crop rotation, the use of seed dressings, early sowing or planting, and the removal of infested plants.<ref>{{cite web |url=http://www.agroatlas.ru/en/content/pests/Delia_antiqua/ |title=''Delia antiqua'' (Meigen): Onion Fly |website=Interactive Agricultural Ecological Atlas of Russia and Neighboring Countries |access-date=2013-03-29 |archive-date=14 May 2013 |archive-url=https://web.archive.org/web/20130514095654/http://www.agroatlas.ru/en/content/pests/Delia_antiqua/ |url-status=live }}</ref>

The onion eelworm (''[[Ditylenchus dipsaci]]''), a tiny parasitic soil-living [[nematode]], causes swollen, distorted foliage. Young plants are killed and older ones produce soft bulbs. No cure is known and affected plants should be uprooted and burned. The site should not be used for growing onions again for several years and should also be avoided for growing [[carrot]]s, [[parsnip]]s, and [[bean]]s, which are also susceptible to the eelworm.<ref>{{cite web |url=http://www.gardenaction.co.uk/techniques/pests/onion_eelworm.htm |title=Onion Eelworm (''Ditylenchus dipsaci'') |year=2011 |website=GardenAction |access-date=2013-03-29 |archive-date=3 February 2013 |archive-url=https://web.archive.org/web/20130203011252/http://www.gardenaction.co.uk/techniques/pests/onion_eelworm.htm |url-status=live }}</ref>

White rot of onions, leeks, and garlic is caused by the soil-borne fungus ''[[Stromatinia cepivora|Sclerotium cepivorum]]''. As the roots rot, the foliage turns yellow and wilts. The bases of the bulbs are attacked and become covered by a fluffy white mass of [[Mycelium|mycelia]], which later produces small, globular black structures called [[Sclerotium|sclerotia]]. These resting structures remain in the soil to reinfect a future crop. No cure for this fungal disease exists, so affected plants should be removed and destroyed and the ground used for unrelated crops in subsequent years.<ref>{{cite web |url=https://www.rhs.org.uk/advice/profile?pid=226 |title=Onion white rot |website=RHS Gardening |publisher=Royal Horticultural Society |access-date=2013-03-29 |archive-date=4 August 2018 |archive-url=https://web.archive.org/web/20180804231507/https://www.rhs.org.uk/advice/profile?pid=226 |url-status=live }}</ref>

Neck rot is a fungal disease affecting onions in storage. It is caused by ''[[Botrytis allii]]'', which attacks the neck and upper parts of the bulb, causing a grey mould to develop. The symptoms often first occur where the bulb has been damaged and spread down the affected scales. Large quantities of [[spore]]s are produced and crust-like sclerotia may also develop. In time, a dry rot sets in and the bulb becomes a dry, mummified structure. This disease may be present throughout the growing period, but only manifests itself when the bulb is in storage. Antifungal seed dressings are available and the disease can be minimised by preventing physical damage to the bulbs at harvesting, careful drying and curing of the mature onions, and correct storage in a cool, dry place with plenty of circulating air.<ref>{{cite web |url=https://www.rhs.org.uk/advice/profile?PID=747 |title=Onion neck rot |website=RHS Gardening |publisher=Royal Horticultural Society |access-date=2013-03-29 |archive-date=4 August 2018 |archive-url=https://web.archive.org/web/20180804231835/https://www.rhs.org.uk/advice/profile?PID=747 |url-status=live }}</ref>

<gallery class=center mode=nolines widths=180 heights=180>
File:Uienvlieg maden.jpg|Larvae of the [[onion fly]]
File:Urocystis colchici var. cepulae on an onion seedling.jpg|Onion smut, ''Urocystis colchici'' var. cepulae, on a seedling
File:Zwiebel Blattfleckenkrankheit (Cladosporium allii-cepae) Anamorph - Noé López G.LLG-Bernburg.jpg|Onion leaf spot caused by ''[[Cladosporium|Cladosporium allii-cepae]]''
File:Onion (Allium cepa) Bacterial soft rot (42052268015).jpg|Bacterial soft rot caused by ''[[Erwinia carotovora]]'' subsp. carotovora
File:Zwiebel Schmutzfleckenkrankheit (Colletotrichum dematium f. sp. circinans) - G-Bedlan, Wien.jpg|[[Anthracnose]] caused by ''[[Colletotrichum dematium]]'' subsp. circinans
</gallery>

Onion oil is authorised for use in the European Union for use as a pesticide against [[carrot fly]] in [[Apiaceae|umbelliferous crops]] (carrots, parsnips, parsley, celery, celeriac).<ref>{{Cite web |last=European Commission |date=20 July 2018 |title=Final Review report for the basic substance Onion Oil finalised in the Standing Committee on Plants, Animals, Food and Feed at its meeting on 20 July 2018 in view of the approval of onion oil as basic substance in accordance with Regulation (EC) No 1107/2009 |url=https://mst.dk/media/171096/review-report-for-onion-oil-juli-2018.pdf |url-status=live |archive-url=https://web.archive.org/web/20211123111251/https://mst.dk/media/171096/review-report-for-onion-oil-juli-2018.pdf |archive-date=23 November 2021 |access-date=23 November 2021}}</ref>

{|class="wikitable" style="float:right; clear:left; width:14em; text-align:center;"
! colspan=2|Production of onions and shallots (green) in 2022
|-
! style="background:#ddf; width:75%;"|Country
! style="background:#ddf; width:25%;"|<small>[[tonne]]s</small>
|-
|{{CHN}}||864,488
|-
|{{MLI}}||610,576
|-
|{{ANG}}||558,480
|-
|{{JAP}}||510,462
|-
|'''World''' ||'''4,970,615'''
|-
|colspan=2|<small>Source: [[UN Food and Agriculture Organization]]<ref name="faostat">{{cite web |url=http://www.fao.org/faostat/en/#data/QC |title=Production of onions and shallots (green) in 2022: Crops/World Regions/Production Quantity/Year from pick lists |publisher=United Nations Food and Agriculture Organization, Statistics Division (FAOSTAT) |date=2024 |access-date=22 May 2024 }}</ref></small>
|}

=== Production ===

[[File:Onion grading at the Centre for Agroecology, Water and Resilience (CAWR), Coventry University.webm|thumb|Onion grading at the [[Centre for Agroecology, Water and Resilience]], England, using a manually-operated sorter]]

Onions are a widely cultivated vegetable crop, produced in the second largest quantity after [[tomato]]es.<ref>{{Cite book |last=Ray |first=Ramesh C. |url=https://books.google.com/books?id=sWH8EAAAQBAJ&dq=global+onion+cultivation&pg=PA283 |title=Roots, Tubers, and Bulb Crop Wastes: Management by Biorefinery Approaches |date=2024 |publisher=Springer Nature |isbn=978-981-99-8266-0 |page=283}}</ref> In 2021, the top global producers of onions were China, India, the United States, and Turkey.<ref>{{Cite journal |last1=Ochar |first1=Kingsley |last2=Kim |first2=Seong-Hoon |date=2023-09-18 |title=Conservation and Global Distribution of Onion (Allium cepa L.) Germplasm for Agricultural Sustainability |journal=Plants |volume=12 |issue=18 |page=3294 |doi=10.3390/plants12183294 |doi-access=free |pmid=37765458 |pmc=10535454 |bibcode=2023Plnts..12.3294O }}</ref> In 2022, world production of onions and shallots (as green produce) was 5.0 million [[tonne]]s, led by [[China]] with 17% of the total, and [[Mali]], [[Angola]], and [[Japan]] as secondary producers.<ref name="faostat"/>

=== Storage ===

In the home, cooking onions and sweet onions are best stored at [[room temperature]], optimally in a single layer, in large mesh bags in a dry, cool, dark, well-ventilated location. In this environment, cooking onions have a shelf life of three to four weeks and sweet onions one to two weeks. Cooking onions will absorb odours from apples and pears. Additionally, they draw moisture from [[vegetable]]s with which they are stored which may cause them to [[Decomposition|decay]].<ref name=almanac /><ref name=Jauron>{{cite web |url=http://www.extension.iastate.edu/news/2009/jul/062201.htm |title=Harvesting and storing onions |last=Jauron |first=Richard |date=2009-07-27 |publisher=Iowa State University Extension |access-date=2013-03-28 |archive-date=18 May 2013 |archive-url=https://web.archive.org/web/20130518151139/http://www.extension.iastate.edu/news/2009/jul/062201.htm |url-status=live }}</ref>

Sweet onions have a greater water and sugar content than cooking onions. This makes them sweeter and milder tasting, but reduces their shelf life. Sweet onions can be stored refrigerated; they have a shelf life of around one month. Irrespective of type, any cut pieces of onion are best tightly wrapped, stored away from other produce, and used within two to three days.<ref name=FAQ />