The knowledge on the critical crop-weed competition period is important for designing an efficient weed management program. Field studies were conducted in 2012 and 2013 at the Agricultural Research Institute, Kahramanmaras, Turkey to determine the effects of three row spacing (50, 70 and 90 cm) on the critical period for weed control (CPWC) in cotton. A four parameter logistic equation was fit to data relating relative crop yield to both increasing duration of weed interference and length of weed-free period. The relative yield of cotton was influenced by the duration of weed-infested or weed-free period, regardless of row spacing. In cotton grown at 50 cm row spacing, the CPWC ranged from 117-526 growing degree days (GDD) (V2-V11 growth stages) in 2012 and 124-508 GDD (V2-V10) in 2013 based on the 5% acceptable yield loss level. At 70 cm row spacing, the CPWC ranged from 98-661 GDD in 2012 (V2-V13) and 144-616 GDD (V2-V12) in 2013. At 90 cm row spacing, the CPWCranged from 80-771 GDD in 2012 (V1-V14) and 83-755 GDD (V1-V14) in 2013. In order to obtain a 95% weed-free yield, the weed management should start at 16 days after crop emergence (DAE) and continued until 52 DAE (V2-V11) for crops grown in 50 cm row spacing, 15 and 60 DAE (V2-V13) for 70 cm row spacing and 11 and 67 DAE (V1-V14) for crops grown in 90 cm row spacing. This suggests that cotton grown in narrow row spacing (50 cm) had greater competiveness against weeds compared with wider row spacing (70 and 90 cm). Cotton growers can benefit from these results by improving cost of weed control through better timing of weed management.