Peppermint (Mentha × piperita L.) is grown in the gardens for its attractive look and multilateral use in the kitchen and medicine. The grown plant spreads very easily producing stolons and could effectively compete with other plant species. For the purpose of this study, the effect of aqueous extracts from dry peppermint leaves was examined on the germination, growth, fresh and dry weight, and electrolytes leakage of 10 species commonly grown in different regions of the world: Beta vulgaris L., Cucumis sativus L., Lactuca sativa L., Lupinus luteus L., Phaseolus vulgaris L., Raphanus sativus L. var. radicula Pers., Sinapis alba L., Lycopersicon esculentum Mill., Triticum aestivum L., and Zea mays L. Several concentrations of the aqueous extracts from peppermint leaves were prepared: 1, 3, 5, 10, and 15%. The seeds germination decreased with increasing concentration of aqueous extracts from peppermint leaves. The seed germination was completely inhibited on Petri dishes with 10 and 15% extracts. The tomato seeds were the most sensitive, they germinated on the distilled water and 1% extract only. The most resistant were the bean seeds that had the highest germination capacity. In general, the growth of seedlings of analyzed species was inhibited by the aqueous extracts from peppermint leaves. However, it was noticed the stimulating effect on the seedling growth of bean and maize on the 1% extract. The aqueous extracts from peppermint leaves caused the electrolyte leakage in all examined species and it raised with increasing extract concentration at the concentration higher than 3%.