A method to improve the function and performance of the mushroom bed comprises nutritionally supplementing the mushroom bed by mixing very small amounts of carboxylic acid salts into the casing layer or on the surface of the compost in close proximity to the casing layer of chalk and peat soils as commercially utilized. The salt may be derived from an aliphatic, alicyclic, heterocyclic or aromatic carboxylic acid and mixtures thereof. The cations may include potassium magnesium and preferably calcium and mixtures thereof for both casing additions and compost surface application. For compost surface additions only, ammonia and organic amines may also be used as cations. The carboxylic salts may be mixed with other nutrient substances to further improve performance.