The effects of a nutrient addition experiment on the plant biomass of garigue vegetation on ultramafic (serpentine) soils in Tuscany, Italy, were investigated. Although community composition was not significantly changed, fertilization had a significant positive influence on biomass production. The most affected species groups were woody species (chamaephytes and phanerophytes), annual grasses and annual forbs; the biomass increase of the perennial grasses and perennial forbs was statistically not significant. Soil extractable elements differed for calcium and potassium in the plots where they were added; sodium and nickel extractabilities were reduced by calcium addition due to the increased soil pH. Biomass production was linked more to major nutrient addition than to reduced nickel extractability, confirming that serpentine vegetation of Tuscany is mainly affected by nutritional stress rather than soil heavy metal content. The addition of calcium had a low effect on primary production of these ultramafic soils.