The aim of the study was determination of the effect of soil phosphorus content on the diversity and dynamics of flora accompanying energy willow (Salix viminalis L.) crops in two time periods. The study was carried out in 2013-2014 in 5-7 years old plantations and in 2018 in 10-11 years old plantations, in three locations of the Łódź voievodeship. Six plantations established in two groups of soils were evaluated: 1) with very low and low phosphorus content and 2) with medium and high phosphorus content. The vegetation accompanying willow was identified based on an analysis of 40 phytosociological relevés. The statistical analysis: PCA and cluster analysis were made. It was found that the vascular flora of Salix viminalis L. differed in the total number of species; 71 species were found in 5-7-year-old plantations, established on soils with a lower phosphorus contents, while on soils with a higher contents, the number of species was 56. In 10-11-year-old Salix viminalis L. crops the number of species was lower in two type of plantations. Perennial plants, dicotyledonous (74%-83%), hemicryptophytes, woodland and shrub, and meadow apophytes dominated in both plantation groups, irrespectively of the study period. Most species belonged to three phytosociological classes: Artemisietea vulgaris, Molinio-Arrhenatheretea, Stellarietea mediae. An analysis of the dynamics of flora, besides decreasing the number of species, showed that perennial species, woodland and shrub apophytes increased in both groups of the plantations. In crops on soils with a lower phosphorus content in the second part of the study period, species from the Artemisietea vulgaris class dominated, and on soils with a higher phosphorus content, species from the Molinio-Arrhenatheretea class. In both periods, legumes had a small share.