The study was conducted to determine the allelopathic effects of Crocus sativus L., Ricinus communis L., Nicotiana tabacum L., Datura inoxia Mill., Nerium oleander L., and Sorghum vulgare L. on the germination and growth of Amaranthus retroflexus (redroot pigweed). Powder and aqueous extracts of these plants were used to run the experiment under laboratory and greenhouse conditions. In the laboratory, all aqueous extracts showed a significant inhibitory effect on the germination, seedling length and weight of redroot pigweed plants. The most allelopathic against the redroot pigweed were R. communis, N. tabacum, and D. inoxia. In the greenhouse experiment, extracts and the powder of these plants also showed significant inhibitory effects on pigweed dry weight, height, leaf area, number of survivor plants, and amount of chlorophyll. In the germination bioassay and application of powder, the inhibitory effect was dosage dependent–the higher the concentration, the strongest the inhibitory effect. From the obtained results, it can be concluded that the powder and extracts of the tested species have an herbicidal potential against redroot pigweed and could be used as natural herbicides and mulches.