A laboratory experiment was planned to search the inhibitory effects of boron (B) concentrations constituted by two sources on seed germination and subsequent seedling growth of sunflower, soybean, and opium poppy. Seven levels (0, 2, 4, 8, 16, 30, 60, and 90 mg B L-1) of boric acid (H3BO3) and sodium borate (Na2B8O13.4H2O) were used. Increasing B levels slightly influenced the germination percentage of sunflower, soybean, and opium poppy. Mean germination time in sunflower and opium poppy was shortened at 60 and 90 mg B L-1 by increasing B, while the germination index was promoted in sunflower. However, seedling growth of sunflower, soybean, and opium poppy was considerably prohibited by B doses. The shoot length of sunflower was decreased at 16 mg B L-1, but low B levels enhanced root length, indicating that shoot growth showed more sensitivity to B doses than root length. The shoot and root length of soybean did not exhibit any significant trends against B levels. The seedling length of opium poppy was diminished at 60 mg B L-1 and above. There were no significant differences between boric acid and sodium borate except for shoot length in soybean, germination percentage and seedling length in opium poppy. It was concluded that there were no toxic effects of B levels up to 90 mg B L-1 on germination of sunflower, soybean, and opium poppy, while seedling growth of sunflower and opium poppy was restricted at 60 and 90 mg B L-1, respectively.