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Clean fallow

A clean fallow is a period during which no crop is planted and the soil is regularly hoed or cultivated to eliminate weeds. The bare soil and regular stirring of the soil provide cues that prompt seed germination (Tillage & germination) and the young weeds are then destroyed. Similarly, the rest period between hoeings gives perennials time to move carbohydrates from storage roots or rhizomes into shoots which are subsequently removed, thereby depleting the storage organs (Exhaust perennial roots).

A period of clean fallow prior to planting is sometimes referred to as a 'stale seedbed' though properly, this term only applies if the weeds are killed without disturbing of the soil surface (e.g., with a propane flame). Other opportunities for clean fallows exist between harvest of early crops (e.g., of spinach or lettuce) and fall crops (e.g., of broccoli), and after the harvest of early crops of potatoes or sweet corn. The optimal time to use a clean fallow for weed management depends on the seasonality of the weeds that are giving you the most severe problems.

Clean fallow tends to destroy soil structure. Usually, only a shallow cultivation is necessary to kill the weeds, and this reduces the problem. Nevertheless, soil-building practices discussed in Tilth and weeding should be used to counteract the damaging effects of clean fallow periods.