The experiment was carried out in a field previously not exposed to herbicides, in which jimsonweed (Datura stramonium L.) and wild hemp (Cannabis sativa spp. spontanea) were the dominant weeds. Using sites identified with global positioning system (GPS) coordinates, changes in abundance of weeds in time were investigated. Before the trial in autumn, soil samples were taken for analysis. Nutrient uptake was determined and compared with the results of the spring plant examinations. One month after the sowing of maize (Zea mays L.), the total number of weeds and the number of weed species present at the sampling sites were determined, and aerial fresh and dry weights of the crop and weed plants were measured. Plant tissue samples were assayed for contents of nitrogen, phosphorus, potassium, and calcium, and data obtained from weedy and weed‐free control areas were compared. Similarly, maize yields were determined, and their dependence on plot weediness was evaluated. We found that uptake of large amounts of nutrients by jimsonweed and wild hemp at the early stage of the development of maize is an important factor in crop‐weed competition.