The aim of this study was to determine the effect of cultivar and row spacing on development of generative tillers and seed yield of redtop (Agrostis gigantea Roth) in the two consecutive production years. The study was based on two strict field experiments conducted in Poland (51 degrees 54' N; 17 degrees 12' E), over 2005-2007 and 2007-2009, respectively. Redtop was sown with row spacings of 24 and 48 cm (factor 1), and studied cultivars were Kita, Mieta and Paula (factor 2). The response of redtop seed yield on growing in diversified row spacing depends on weather conditions. In the years when precipitations are well distributed, the use of row spacing of 24 cm had a more favourable effect than 48 cm. In the case of low precipitations in May and June, the highest seed yield could be obtained in row spacing of 48 cm. The redtop cultivars have different reproductive ability. Among studied cultivars, cv. Kita gave the highest seed yield in the first and second production years. Only in the first production year the seed yield of cv. Mieta was lower than that of cv. Paula.