Summary.Seeds ofAvena fatuaandA. ludovicianawere sown at a depth of 15 cm or mixed into the top 5 cm of soil in small field‐plots at Rothamsted and subjected to 5 different regimes of depth and frequency of cultivation for 3 years, after which all plots were dug to 15 cm in spring and autumn for a further 4 years. Seedlings were counted and no plants were allowed to produce seeds. After 7 years, soil‐samples showed that very few intact seeds ofA. fatuaand none ofA. ludovicianaremained, although less than 20% of the seeds sown had produced seedlings. Laboratory tests after 4 to 8 years’dry slorage showed seeds of both species to be viable. The maximum survival of viable seeds, estimated by seedling‐emergence, was 61 months forA. fatuaand 33 months forA. Indoviciana. Seeds ofA. fatuasurvived slightly longer at 15 cm than in the top 5 cm of soil. Survival ofA. ludovicianawas less affected by depth and cultivation, except that birds ate some shallow‐sown spikelets in the first fortnight after sowing.A. fatuagerminated in spring and autumn, andA. tudovicianain winter, irrespective of age of seed and cultivation of soil. Frozen soil delayed emergence ofA. ludovicianaseedlings lor varying periods between December and March. Seedlings ofA. ludovicianawere slightly more winter‐hardy thanA. fatua. More seedlings ofA. fatuaappeared in the second spring than at any other time, but 80% of the seedlings ofA. ludovicianaappeared in the first autumn and winter.Effets de la profondeur d'enfouissement des graines et de la fréquence des façons culturalles sur la longévité et la germination des semences de Folle‐Avoine(Avena fatuaL. etA