In sown field margin stripes or pluriannual forage crops, arable weeds are exposed to high competition and regular mowing or hay cutting, to which they may react very differently. A greenhouse experiment permitted to understand some key factors shaping the ability of common arable weeds and forage crops to grow after such cuttings. Even without competition, cutting shoots at 5cm height reduced biomass production of all 10 species studied, but 6 annual broadleaf weeds were much more affected than 2 perennial forage crops (Dactylis, Medicago) and 2 annual grasses (Alopecurus, Bromus), confirming our hypothesis. Variation of regrowth speed within each species was always positively related to the plant size before cutting, suggesting that bigger plants can remobilize more belowground resources. But this is only true for plants sown at the same date, as older weeds showed reduced regrowth despite their bigger size. Carbohydrate resources of older plants might have already been depleted for reproductive growth. This basic knowledge may be used to construct weed demography models and to develop innovative cropping systems. If most annual weeds cannot grow and reproduce when cut under real conditions with competition, introducing mown temporary grasslands into crop rotations may readily be used as an element of Integrated Weed Management.