Little is known about spatial and temporal characteristics of root formation in spring wheat and its modification by genotypes, nitrogen (N) supply and environments. For two years, three spring wheat genotypes (cv. Albis and Toronit and the experimental line L94491), identified to vary in N use efficiency characteristics, were grown in lysimeters of 1.1 m soil depth. The cultivar Toronit was grown in two more years. The genotypes were either fertilized with 250 kg N ha-1 (HN) or not (LN) in each cropping season. Root growth was regularly screened at different soil depths using minirhizotrons. Cumulative root counts from minirhizotron observations were fitted to the logistic equation in order to compare patterns of root development. Root formation in time, as measured by cumulative root counts, was characterized by three distinct phases: an initial slow growth, a period of rapid increase and a final decrease in growth intensity. Maximum root counts and lengths observed at each depth and during specific developmental stages changed remarkably among the years. The proportion of roots formed between anthesis and physiological maturity ranged from 2 to 19 % of total root production during the crop season, demonstrating that root growth of spring wheat can still be very important after anthesis. All parameters of the logistic growth equation were influenced to some degree by the study factors, indicating a high plasticity of the root system to respond to different soil conditions. However, a single main genotype effect was observed among all tested factors: the asymptotic root count was significantly higher for Toronit as compared to Albis and especially to L94491 in the topsoil (0.10 and 0.25 m). N supply enhanced root counts in the entire soil profile and extended the period of rapid root formation, however, N did not modified the patterns of root distribution with depth.