The data presented are growth and physiological measurements from an ozone exposure experiment, during which grassland forbs, Leontodon hispidus and Succisa pratensis were exposed to low, medium and high ozone treatments over three growing seasons, using an outdoor Free Air Ozone Enrichment system, and with and without the addition of nitrogen during the first year. The plants were planted in April 2016 and were exposed to Low, Medium and High ozone treatments over three growing seasons (May to September 2016-2018). Measurements were taken of light-saturated photosynthesis, stomatal conductance, chlorophyll index, number of flowering stems, leaf ground cover, and the dried weight of litter. All measurements were made by members of the project. The experiments were carried out in the UKCEH Bangor Air Pollution Facility. Work was funded by the UK Centre for Ecology & Hydrology under the Natural Environment Research Council (UK) grant/award NEC05574. For L. hispidus a lower leaf cover was observed with elevated ozone, and there was an increase in litter with added nitrogen. For S. pratensis, elevated ozone reduced flowering and increased foliar damage. Increased litter and accelerated winter die-back with both ozone and nitrogen were also recorded for S. pratensis. These effects have implications for inter- and intra-specific competition, seed establishment, nutrient cycling, as well as the provision of general pollinator resources and highlight the need for concerted action to reduce pre-cursor ozone emissions to go alongside habitat management efforts to protect biodiversity. Full details about this dataset can be found at https://doi.org/10.5285/382baaf2-7795-4aa8-a434-56c9e6bd1516