Disclosed are compositions and processes for the preservation of porous materials, particularly porous fibrous materials, such as wood, wood composites, other processed wood materials, paper, board, card, textiles, rope, cordage and leather. Also for horticultural and agricultural application to plants or growing media prevent the growth and spread of fungal and other disease. The compositions contain salts of one or more preservative metals and carboxylic acids having one or a plurality of hydroxyl groups rendered soluble by means of complex formation with boric acid or a water soluble salt thereof. Application of the compositions of this invention to the porous organic material may be by any means used with conventional preservative solutions, for example soaking, spraying, brushing and vacuum or pressure application or other contact of the solution with the material to be treated.