The ability of Cyanobacteria and green algae to improve physiological activity and plant development gives a promising perspective and has a useful potential in practice, although literature concerning this issue is scanty. The purpose of this study was to assess the influence of two species of Cyanobacteria (Microcystis aeruginosa MKR 0105, Anabaena sp. PCC 7120) and one of green algae (Chlorella sp.) on select physiological processes, determining rooting of cuttings and the subsequent growth of willow (Salix viminalis L.) plants. Two procedures were used to apply sonicated and unsonicated monocultures of Cyanobacteria and green algae to woody cuttings: (i) four-day soaking of cuttings which were then rooted in universal horticulture substrate in a vegetation chamber or in a field and watered with tap water, and (ii) moistening the substrate in which the untreated cuttings were subsequently rooted and plants were grown. The cuttings treated with water, GA₃, IBA, Bio-Algeen S90, and environmental sample were the control. The results show that the used monocultures of Cyanobacteria and green algae significantly stimulated some metabolic processes, thus having an important impact on plant development. Their application increased the stability of cytomembranes and intensified activity of net photosynthesis, transpiration, stomatal conductance, dehydrogenases, RNase, acid, and alkaline phosphatase, and decreased intercellular CO₂ concentration in the rooted cuttings and plants. These physiological events caused increased rooting of willow cuttings and plant growth under laboratory and field conditions.