In 2010, a split-plot experiment was set up in Poland in order to determine the follow-up effect of the white clover intercropping system on biomass and morphology of willow. In 2010 willow was planted in a pure stand and intercropped with white clover. In 2013, after willow achieved a proper growth stage (2010–2012), plant measurements were made in the years 2013–2014. The experiment was carried out with two factors in a split-plot design: the first factor was the cultivation system (main plot) (a) without white clover and (b) with white clover, and the second factor was three basket willow clones: 1047, 1052 and 1057 (subplot). The investigated characters were biomass yield, height of plants, shoot diameter and plant loss. No N fertilization or pesticides were used. The intercropping system (willow with white clover) reduced the number of willow plants, but the willow height was lower in the pure stand (368 cm) than in the intercropping system (409 cm). The highest dry matter yield (30.8 t ha−1), crude ash yield (434 kg ha−1) and macronutrient (N, P, K and Mg) content were obtained with clone 1047.