Slievecallan has a wet oceanic climate with an average annual rainfall of 2,000 mm and high average wind speeds. This is due to the proximity of the ocean (just 8 kilometres away) and its prominence in the landscape. Geologically the soils are a mixture of peat, peaty gley and gley soils over horizontal layers of carboniferous shale, sandstone, and mudstone. The soil is relatively poor in nutrients.