Athletic fields and golf course greens are often constructed of calcareous sands. Supplemental calcium (Ca) applications are frequently recommended to these areas based on the belief that theCa from the calcium carbonate (CaC03) in the medium has limited availability to the plant. The objectives of this study were to determine if applications of additional Ca to grass grown on calcareous sand 1) increase the amount of Ca absorbed by the plant, 2) increase the clipping yield and quality of the grass plant, and 3) affect the availability of other nutrients. 'Midnight' Kentucky bluegrass (Poa pratensis L.) and 'Penncross' creeping bentgrass (Agrostis palustris Huds.) were grown on calcareous sand during two greenhouse experiments. Treatments included a control, calcium sulfate (CaS04), calcium carbonate (CaC03), calcium nitrate [Ca(N03) 2·4H20], and calcium chelate incorporated into the media at 23 g·m-2 Ca. There were no differences inCa tissue content in response to Ca treatment for either species grown on calcareous sand. However, during the first year, calcium nitrate applied to creeping bentgrass reduced the leaf Mg concentration by 15%. A two-year field trial was established on a calcareous sand-based 'Crenshaw' creeping bentgrass green. The same five treatments from the greenhouse trial were utilized, but the rate was split into 5 monthly applications at 4.5 g Ca·m-2 per month. Urea was added to balance the nitrogen (N) found in the calcium nitrate and calcium chelate treatments. Throughout the experiment, there were no differences in tissue Ca content, visual quality or clipping yield in response to the Ca treatments. However, during the first year, creeping bentgrass grown in plots receiving gypsum contained 11% less Mg than the creeping bentgrass in the control plots, which may suggest that excess Ca can be detrimental to the uptake of magnesium. Since there were no increases in Ca content or quality and there were some possible detrimental Ca-Mg interactions, supplemental Ca applications to grasses established on calcareous sand are not recommended.