Modified rosin-paraffin wax resins were found to be efficient as controlled delivery systems for potassium sulfate. Matrix-type formulations were fabricated and dissolution tests performed to determine the influence of individual parameters on fertilizer release rate. Differential scanning calorimetry runs were employed to investigate possible matrix-fertilizer interactions. The mechanism governing K2SO4 release from the matrix was proved to be diffusion-controlled. As a consequence, the release rate was directly related to fertilizer concentration in the matrix. Modified rosin content was of major importance to the release rate, while fertilizer particle size, as well as the geometry of the formulations played a significant role in the diffusion of K2SO4 from the matrix. Moreover, the fabrication of the fertilizing forms is very simple, low in cost and energy demands.