An investigation was carried out on the structure of 14 horticultural substrates, applied to plant cultivation in containers. Special preparations – soil blocks were used for the morphologic analysis of the structure. They had been prepared, earlier, by saturation of prepared samples of the beds with a solution of Polimal-109 polyester resin. The samples were prepared inside boxes of dimensions 8 x 9 x 4 cm, from the substrates, piled loosely at a degree of moisture corresponding to the field water capacity (–9.81 kPa). The polished surfaces of the soil blocks were used to prepare the real images of the structure, after saving in computer memory, at a resolution of 600 x 600 points per inch. It was found out that the structure of the two groups of investigated beds – the mineral and the organic ones – differed considerably. In the loose organic beds fully formed aggregate structure occurred most frequently, while the single grains structure was characteristic for most of the mineral beds.