Brownfield sites contribute significantly to urban biodiversity due to their high spatio-temporal dynamics and their transient character. Plant species richness is, among other factors, contingent on vegetation structure. In this study, we examined plant species richness, vegetation height, vegetation density and soil parameters of a chronosequence of urban brownfield sites in Bremen and Berlin, Germany. These parameters were linked to successional age using single and multiple linear regression. Most biotic and abiotic variables differed significantly between sites with and without brick rubble in the soil, indicating a strong effect of site history on vegetation development. Soil parameters of the sites were not clearly linked to site age. Vegetation height and density increased significantly over time. Additionally, height and density increased with soil phosphorus content and water permeability of the soil, whilst plant available water only contributed to the model of vegetation density. Species richness increased with vegetation height but decreased with vegetation density. This indicates that species richness is maximised when a community comprises a mixture of early and mid-successional species. The results suggest that high plant species richness on sandy brownfield sites can be achieved by strong disturbances at an interval of 5 (±2) years. However, limiting soil resources can prolong this interval considerably. Management aiming to maximise plant species richness in urban brownfield sites should therefore take into account the interplay between soil resources and site age.