Botanical composition and dry mass yielding of meadow (M) and pasture (P) mixtures (designed - M1 and P1, market - M2 and P2, control, simplified - M3 and P3) and species or varieties (Dactylis glomerata - M4 and Lolium perenne (4n)- P4) intended for organic grasslands on mud-peat-muck organic soils were studied in the years 2006-2010. Pasture mixtures were mown 5 times a year and meadow mixtures - 3 times a year. The smallest changes were observed in mixtures P1 and M1. Most stable in pasture management were: Poa pratensis, Phleum pratense, Festuca rubra while Festuca pratensis, Agrostis giganthea and Trifolium repens retreated from sward. Lolium perenne and L multiflorum maintained a high share for 4 years of experiment. Most stable on meadows were: Poa pratensis and Festuca rubra and Lolium perenne. Legumes Trifolium hybridum and T. pratense retreated while T. repens maintained 10% share for 2 years. Percentage share of Dactylis glomerata was very large for 2 years and large for the next two years similarly to the share of Festuca pratensis and Phleum pratense. Dry mass yields depended more on thermal and moisture conditions than on the type of mixture but the largest dry mass yield for 4 study years was obtained from meadow designed M1 mixture - Festuca pratensis (19%), Festuca arundinacea (20%), Phleum pratense (20%), Dactylis glomerata (5%), Poa pratenis (13%), Festuca rubra (10%), Trifolium hybridum (8%), Trifolium pratense (5%). Observed disappearance of differences resulting from the composition of sown mixtures. However, proper selection of species and varieties and multi-species composition of mixtures may slow down this process in subsequent years due to diverse developmental dynamics of particular components.