The objective of this experiment was to: 1) examine the degree of influence of hereditary factors and conditions of growth (region of cultivation, season of growth and type of cultivation) on the phenotypic variance of leafiness in breeding populations of red clover; 2) quantify heritability and experimental variances in order to assess the opportunities for red clover breeding for improved leafiness. Five genotypes of red clover (four synthetic breeding populations and variety Sofia 52) were screened in the study. Among the factors studied as environmental variables, the season of growth had the strongest effect on the leafiness of red clover. In second vegetation of the life cycle of plants there was a significant additive genetic variance (hns 2 = 0.31) of the trait of leaf proportion in the fresh forage and the recurrent phenotypic selection for this criterion could be used in the breeding for leafiness in this species. It can be concluded from the results in this experiment that a higher degree of heritable genetic variation of leafiness must be searched for in connection with the variation of additional characteristics - thickness of stems, rates of formation and growth of stems, growth features related to regrowth (secondary growth) and age of sward (plants) and probably to persistence of genotypes.