This work focused on the investigation and evaluation of the effects of weeds on the agronomy of Celosia argentea at various weed densities. Five levels of crop – weed competition were introduced into a 20 X 10 m2 C. argentea plot comprising: 100% weediness (No weeding all through the period), 75% weediness (Weeding on the first 2 weeks only), 50% weediness (Weeding on the first 4 weeks), 25% weediness (Weeding for 6 weeks) and 0% weediness (Weeding all through the period) in a randomized complete block design (RCBD) with three replications. The experiment was conducted for 8 weeks; during which data were collected on the agronomic and yield variables of the crop. These variables were subjected to analysis of variance and the significant means were separated using Duncan’s multiple range tests. There was obvious competition between the crop and the weeds growing on the plots, evident by reduced agronomic and yield performance of the crop under plots of higher weed incidence. The duration of competition also contributed to significant decline in crop performance as weed density induced significant reduction in plant population and plant height. The results point to the direction that optimum agronomic and yield performance of the crop is obtained where there is reduced incidence of weeds and better management of weed population.