The aim of the bachelor thesis was to examine the effects of natural extracts obtained from white willow (Salix alba L.), silver birch (Betula pendula L.), nettle (Urtica dioica L.) and thyme (Thymus vulgaris L.) in various combinations on growth and immunity of selected plant species. In the first part of the experiment, the efficacy of plant extracts on the growth of plants was examined. Plant extracts were sprayed directly on leaves of model plants. The increase in biomass was derived from the increase in dry matter weight of the treated plants compared to the control group. As model plant species were selected peas, beans, tomatoes, cucumbers, turnips, oats and radish. Based on the screening test and the overall concept of the thesis, combined 1 : 1 nettle and willow bark extract (whose efficacy has been proved) and thyme extract were chosen for the further stages of experiment where they were tested in four concentrations on peas, oats and tomatoes. In the second part of the experiment, the impact of thyme extract at 5 % concentration on the fecundity of pea aphid (Acyrthosiphon pisum Harris, 1776) was observed. The population of aphids on pea plants has been observed during 9 days. Variant with no treatment (control), variant with treatment one day before the deployment of aphid nymphs on plants and variant with treatment one day after the deployment of aphid nymphs were compared. The most significant decrease in parental population was found in the variant with treatment one day after the deployment of the pest (88 % mortality within 24 hours after the treatment). The impact of thyme extract on fecundity has not been proved. It was found that the difference of increase in filial population among variants was given by the number of insects in the parental generation that have grown into the fertile age. For the statistical analysis of data from all parts of the experiment the one – way analysis of variance ANOVA and Tukey HSD 95 % test were used. For the evaluation of the population of pea aphid linear regression analysis was applied.