The results of research on the activation of the microflora by using post–harvest green manure crops were presented. As a result of the conducted studies, the positive effect of sidereal crops of Raphanus sativum and Phacelia tanacetifolia on activity increase of microflora in black soil with little humus was revealed. Application of post–harvest siderates increased the number of non–sporous species of bacteria and actinomycetales, contributed to improvement of soil environment under the influence of siderates, which had a positive effect on creating more comfortable conditions for growing potatoes. The usage of green fertilizers had a positive influence on microbiology activity of soil. Keywords: siderates (green manure), media, Phacelia tanacetifolia, Raphanus sativum, Fagopyrum sagittatum, Actinomycetales, Lepidium sativum.