Phacelia tanacetifolia Benth. is a melliferous, phytosanitary fodder plant. An important factor in understanding the biology of this plant is to investigate its allelopathic potential. In the experiment conducted here, ×Triticosecale Wittm. cv. Mamut was treated with water extracts from the roots, stems, leaves, and flowers of phacelia at concentrations of 10%, 12.5%, 15%, and control with 0% of extract. After 7 days of exposure, the germination of grains was assessed by analysing, seedling growth, mass parameters, water content, and electrolytes leakage. Aqueous extracts from the stalks, leaves, and flowers of phacelia significantly inhibited kernel germination at a 10% concentration, and from roots at a 12.5% concentration. The elongation growth of triticale seedlings was significantly inhibited by each of the extracts. Extracts from the leaves and flowers caused a significant reduction in fresh mass at a 10% concentration and extracts from the stalks at a 12.5% concentration. A significant reduction in water content was also found in seedlings watered with extracts of 10% from roots, stalks, and leaves and 12.5% from flowers. Extracts from phacelia roots at a 12.5% concentration and extracts from stalks, leaves, and flowers at a 10% concentration significantly increased the leakage of electrolytes. In general, phacelia exhibits allelopathic potential at higher concentrations of extracts.