As the population of the world increases, the demand for food, food security and, hence, maximizing yield is becoming a challenging issue for modern agriculture. Over the last decades, the application of chemicals like fertilizers, pesticides and herbicides has increased dramatically. Despite improvements in plant breeding programs reducing the demand for chemicals, herbicide use is still increasing worldwide. According to the literature, continuous use of heavy doses of chemicals is encouraging the development of resistance in different weed species and endangering the ecosystem. Consequently, resistance development among weeds to herbicides is of great concern. Now, some research efforts are concentrated on finding some natural extracts to control this threat, thereby reducing the use of herbicides in future. In general, the term allelopathy refers to the chemical interaction between plants in which one plant may be affected by another plant’s chemical extracts. An experiment was designed and conducted to examine the effects of some extracts obtained from three plants (wheat, barley and rapeseed) on the number and speed of seeds germinated as well as the early growth of 3 weed species (barnyard grass, lambs quarters and redroot amaranth) and one goal crop (tomato). In addition, distilled water was used as a control treatment. The experiment was conducted under two conditions: laboratory and glasshouse, based on a randomized complete block design. Collected data were exposed to advanced statistical analysis including ANOVA and multivariate analysis (PCA). The results indicated that some extracts can reduce the germination and early growth of certain weeds and crop, for example weed extract on barnyard grass, rapeseed extract on tomato and redroot amaranth. Thereby the application of these extracts may effectively control some weeds such as barnyard grass and redroot amaranth. However, some other extracts positively affected the rate and speed of germination of some plants. For example, rapeseed extracts increased barnyard grass germination and early growth. This result indicated the caution of using of specific extracts on plants.