Dataset includes concentration of crude protein, fibre (ADF and NDF), metabolisable energy (ME) and a range of dietary minerals from three species-rich floodplain meadows in Central England. Samples were taken between May and September in 2020 and 2021. Graminoid:forb ratio, Accumulated Growing Degree-days (thermal time), Accumulated Actual Evapotranspiration and yield are recorded for each date. The data were originally collected to investigate the seasonal dynamics of yield, dietary minerals, protein and energy in floodplain meadow hay. For full study method see https://doi.org/10.21954/ou.ro.00097871 Full details about this dataset can be found at https://doi.org/10.5285/361f0587-4cc6-48df-9f7e-8ade331cf8d5