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 The onion crop cycle (Allium cepa L.)

The onion cycle has 10 development stages, from planting to bulb maturity. Learning to recognize each stage is essential to implement an efficient crop management program.

Seed
Seed in soil after planting.

Pre-emergence
Underground germination before emergence of the cotyledon. Key stage in an integrated weed management program.

Germination
After the underground germination, the cotyledon appears. It looks like an arch.

     

First leaf
When the first leaf emerges [1], the plant is still in the flag stage.

Cotyledon fall
After a progessive drying out and the emergence of leaves 2 and 3, the cotyledon falls. This stage is very important for an integrated weed control program.

Fall of first leaf
After the first leaf dries out and falls, the second leaf falls while the 5th, 6th and 7th leaves appear.

   

Bulb forming
The bulb starts to form; the 2nd and 3rd leaves dry out while leaves 8 to 13 appear; the plant is at its maximum development.

Bulb thickening
Beginning of the regression of the vegetative phase. Drying out of leaves 4, 5 and 6 and of the end of the main leaves: due to their weight, some leaves fold; new smaller leaves may appear; the bulb becomes visible; the tunic starts to form. Note the shallow root system at this stage. Care must be taken not to prune these roots wih cultivation.

Laying down plant
The vegetative phase is over; The leaves lay down on the soil and start to dry out. The bulb has almost reached its final size.

Bulb maturity
The tunic is finished. The leaves and the neck are completely dry. When harvested, the bulb, completely closed, is seperated from the aerial part.

 

      

 

Source: Drawings based on data from Ch. Rey, J. Stahl, Ph. Antonin, G. Neury. In L'oignon de garde, CTIFL ed, Paris, France.

 

The crop is characterized by a slow germination and growth speed as well as a shallow root system which musn't be injured. The cycle length depends on the variety and ranges from 120 to 180 days.

Soil types
Onions will grow in a wide range of soil types. We recommend however the choice of friable soils; their high water retention potential will preserve the shallow root system. Avoid heavy clay soils which can block root growth and lead to problems at harvest.

Ecophysiology - bulb
A minimum day-length is necessary for bulb formation. The threshold value depends on varieties: around 12 to 13 hours for tropical areas. Bulb thickening is related to outdoor temperature: temperatures above 18°C start bulb thickening.

Nutrient requirements
For nitrogen, the crop requirement not only depends on yields but also on the product destination (i.e market demand).

 

 

© ICS 2002 - 2009
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Document created : june 2002 - updated : juillet 7, 2009

Publication director : Jean-François MARTIN - ICS - 12 rue du Soleil, ZA Croix-Fort - 17220 La Jarrie - France

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