The optimum harvest date in spring is a problem that divides producers. Is it better to focus on forage quality with an early cut, or quantity with a later harvest? Trials were carried out on mown grasslands from 2014 to 2016 as part of the «Progrès-herbe» [= «Progress Grass»] and «Preparing Forage Production for Climate Change» projects. The issue of forage shortages in dry conditions was approached from the specific angle of the influence of the period of the first cut and the rest interval in the summer. Results indicate that dry-matter production and the phenology of cocksfoot are well correlated with the sum of spring temperatures. References for describing the first grassland cycle are proposed: from 200 degree-days = start of vegetation growth; from 500 degree-days = drop in the nutritional value of the grass; from 600 to 750 degree-days = heading of the cocksfoot. To optimise annual production with five cuts per year, the first cut takes place when the sum of the temperatures lies between 640 and 740 degree days, i.e. at the time of the heading of the cocksfoot. In summer, it is unwise to mow grasslands when conditions are at their hottest and driest. A two-week delay in July-August has no negative effects on end-of-season production.
When must intensive grassland be mown?