In the search for a standard bioassay of phytotoxicity for allelochemicals, 22 commercial varieties of eight plant species [four dicotyledons: lettuce (Compositae), carrot (Umbelliferae), cress (Cruciferae), tomato (Solanaceae); and four monocotyledons: onion (Liliaceae), barley, wheat, and corn (Gramineae)] proposed as models for the most common weed families have been tested at different pH and solution volumes per set conditions. Nine commercial varieties selected as standard target species (STS) were tested with standard commercial herbicides to ensure their sensitivity to phytotoxic compounds. Results are discussed to establish the proper growth requirements, and sensitivity of commercial seeds of STS and to find the most suitable commercial herbicides that allow comparison with an internal standard to validate the response of potential allelochemicals.