Green manures are plowed under during field preparatio n to enhance fertility and soil tilth, whereas cover crops may be plowed or managed as residues on the soil surface. Weeds are suppressed within cover crops during germination and establishment, while the cover crop is growing, or following dessication and kill. Other barleys provide moderate weed suppression by establishing while weeds are developing or demonstrate upright or prostrate growth forms. During the cover crop growth phase, weeds are suppressed depending on the amount of biomass and when it is produced in relation to weed development or maturation. Most cereals produce maximum growth during mid-winter or early spring.
Legumes tend to mature in late spring, often with a healthy mixture of various weeds.
Mixtures of cereals and legumes will reduce weed growth and potential infestations compared to legumes alone. Controlling cover crops in mid-winter or early spring requires timing in relation to management of the total biomass or residue. Greater amounts may require mowing, chopping, flailing, or rolling. Many mature covers can be handled mechanically with minimal regrowth. If herbicides are used, treatment must penetrate a reasonable amount of the foliage.