Abstract: In agricultural areas, field margins are often the only remaining habitat for wild plant species. However, due to their proximity to agricultural fields, the vegetation of field margins may be affected by agrochemicals applied to the crop field. To investigate individual and combined effects of fertilizer, herbicide, and insecticide inputs on the plant community of field margins, a 3-year field study with a randomized block design was performed. The applied fertilizer rates (25% of the field rate) and pesticide rates (30% of the field rate) were consistent with their average input rates (drift + overspray) in the first meter of a field margin directly adjacent to the field. Fertilizer and herbicide applications resulted in significantly reduced frequencies of several plant species. The fertilizer promoted plants with a high nutrient uptake and decreased the frequencies of small and subordinate species. In addition to the disappearance of a few species, the herbicide caused predominantly sublethal effects, which gradually reduced the frequencies of certain species. Significant herbicide–fertilizer interaction effects were also observed and could not be extrapolated from individual effects. The impacts of both agrochemicals became stronger over time, led to shifts in plant community compositions, and caused significantly lower species diversities than in the control plots. The insecticide application significantly affected the frequencies of two plant species. The results suggest that a continuous annual application of agrochemicals would cause further plant community shifts. Hence, to preserve biodiversity of agricultural landscapes, it is recommended to protect the vegetation in field margins from agrochemical inputs.