One of the most commonly known allelopathic species is black walnut (Juglans nigra), which releases a compound called juglone in its leaves, stems, fruits, and roots. This plant causes stunted growth in many ornamentals, including rhododendrons and azaleas, and vegetables such as tomatoes, peppers, and potatoes. However, some plants, such as mock orange, forsythia, and garden plants such as squash, beans, and onions, are OK to plant near these trees.
