Controlling weed development during the onion crop cycle is essential to obtain high yields and marketable products. Onions do not compete well with weeds: they are slow growing and can suffer from successive flushes of weeds; they have narrow upright leaves which do not shade out weeds that emerge in the rows. For most crops it is often possible to choose between mechanical or chemical control. But with onions, the plant and crop characteristics make mechanical solutions difficult to use after planting:

• They are shallow rooted, which makes cultivation difficult because it might prune the roots. Mechanical cultivation for example must be avoided when onions begin to bulb.
• The crop is planted at high densities which leaves no room for mechanical cultivation in the rows. Hand weeding is used in some countries but is very time consuming.

Moreover, the selection of herbicides is often limited because of legislation (different from one country to another), efficiency, effects on onion plants (serious damage risk) and price. It is therefore essential to built an integrated weed management program, combining cultural practices and herbicides. It is defined according to each situation. This page displays some basic information on such programs.

Since onion crops are not competitive against weeds, many species (grass or broad leaf, annual or perennial) may grow in your parcels. The composition of each weed population is highly variable; it depends on many factors such as soil type, crop rotation, sowing and growing period etc. You can refer to our useful links to find different weed population lists.

We recommend you choose the most weed-free fields, plan the planting in advance, identify and map weeds and, of course, keep records over the years. Although simple, these basic principles are the key to a successful crop.

NON CHEMICAL control is possible before germination. We strongly recommend the use of the Väderstad Carrier which perfectly controls the working depth and performs a shallow cultivation that will avoid bringing deep weeds into the top soil layer. It will also facilitate an even weed emergence.

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. 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 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).