Green manure refers to plants that have been uprooted and laid on top of the soil where they will decay and provide nutrients to the soil and remaining plants. Unlike chop and drop mulching where the plants are continually cut and allowed to regrow, plants used for green manure are uprooted and die. Weeds that have not yet gone to seed can and should be used as green manure. The existence of certain weeds indicates the lack of some aspect (nutrient or condition) of the soil. Using these weeds as green manure will allow the nutrients that they have acquired to be introduced into the soil.