This paper investigates the effect that manipulation of soil and vegetation conditions has on plant community development during attempts to create neutral hay meadow communities on a clay-capped landfill in Somerset, United Kingdom. The objectives are (1) to determine the effect of manipulation of soil and vegetation on the development of the target plant community, (2) to identify whether these treatments had an effect on edaphic factors (physical and chemical properties, earthworm populations), and (3) to establish which, if any, of these edaphic parameters are underlying factors in determining the vascular plant community composition. In 2001 a commercial hay meadow seed mix was sown on three substrate treatments: (i) bare clay, (ii) a mixture of topsoil and compost ameliorant in equal proportions, and (iii) over naturally colonized vegetation. Plant community development and edaphic factors were monitored between 2001 and 2007. Although initially the presence of ameliorant promoted germination and growth of seeded species, after 2004 nonseeded competitive grasses dominated the sward. Where ameliorant was removed the target community continued to develop proving this to be the most successful treatment. This was found to be a due to suppression of competition from Elytrigia repens (Common couch), which grew most abundantly on soils with high organic matter and high soil water levels within the soil. Contrary to previous research, Trifolium repens (white clover) was not found to reduce forb diversity in this study. No evidence was found of earthworm abundance affecting plant community development.