Weed competition can dramatically affect the growth of hybrid poplar in the prairies. The objective of this study was to investigate the effects of dandelion (Taraxacum officinale) and quackgrass (Elytrigia repens) weed species on the growth of hybrid poplar and to obtain input parameters for N uptake modeling. Single hybrid poplar (SHP) was grown in pots along with different densities of dandelion (D) and quackgrass (QG) weeds (SHP, SHP+4D, SHP+8D, SHP+1QG and SHP+3QG) in two soils (Alfalfa and Pasture sites) collected near Meadow Lake, Saskatchewan. Hybrid poplar and weeds were harvested at 47 and 97 days for Pasture soil and at 49 and 102 days for Alfalfa soil. The growth of hybrid poplar was severely affected in the presence of dandelion and quackgrass weeds; however, this effect was more pronounced at the second harvesting stage. Shoot biomass for SHP was 28 and 22 g for the Pasture and Alfalfa sites, respectively while SHP shoot biomass with dandelion or quackgrass weed competition varied from 0.54 to 0.81 and 0.3 to 3.66 g, respectively. Similar observations were also obtained with other growth parameters such as tree height, root collar diameter and fresh root biomass. During the growing period soil solution N concentration decreased several-fold in both soils, however, the magnitude of decrease was comparatively higher in weed treatments. Nitrogen uptake of 263 and 390 mg pot-1 for hybrid poplar was observed in the SHP treatment for Pasture and Alfalfa soils, respectively. The corresponding N uptake for hybrid poplar grown along with dandelion or quackgrass varied from 4 to 24 and 4 to 8 mg pot-1, respectively. These measured soil and plant parameters along with other required parameters will be used for modeling N uptake by hybrid poplar in competition with weeds using the SSAND model.