To facilitate the maintenance and restoration of semi-natural grasslands, it is important to understand their relationships with soil properties. Semi-natural grasslands typically have a high incidence of stress-tolerant species (measured here by high stress radius values), but not all have high species richness. Species richness and stress radius values were related to soil pH, Olsen extractable phosphorus (P), extractable potassium (K) and magnesium (Mg), total nitrogen (N) and organic matter (OM) at 571 sites representing a wide range oftemperate grasslands. Highest species richness (>30 m−2) occurred at pH > 6 and 4–15 mg l−1 P, but species richness was also highly variable at 4–15 mg l−1 P. At pH < 5, species richness was low (<20 m−2). Stress radius values were highest (mainly calcareous and heath grasslands and mires) at pH c. 8·0 and < 5·0, and at the lowest soil P levels (<5 mg l−1). A wide range of stress radius values occurred at low soil P levels because appropriate management is also needed to maintain semi-natural grasslands. Reducing soil P is difficult in practice, so grassland restoration in the presence of elevated soil-extractable P levels merits re-assessment.