Abstract: The results of applying (post-em.) micronutrients (1.5 mg L-1), yeast (2.5, 5, 7.5 g), thiamine and riboflavin (25, 50, 75 mg/each) have shown great activity on increasing growth and yield productivity of flax cv. Giza 5 with no advantage set of one upon another, particularly when applied individually not in mixture. Yet, the combined application of the two vitamins plus micronutrients was, to some extent, much more effective. Applying riboflavin plus micronutrients precisely at the moderate concentration of riboflavin (50 mg L-1) was the best in this regard. The data recorded in that 13.33-189.74% increment in growth and up to 63.23% in yield productivity. Hand weeded was almost good, causing significant increments in crop growth and yield productivity estimated by up to 163.15 and 92.25%, respectively. Significant results were also reported on increasing oil yield percentage of all crop treatments. On the opposite side of the activity, weeds growth were also affected (a reduction effect was occurred) and the most significant results (76.19-85.71% inhibition) were also obtained with applying riboflavin plus micronutrients at 50+1.5 mg L-1. There is a strong thought to be believed that increasing the competitive and/or the allelopathic ability of flax-treated plants could be the real reason behind this authority. Increasing growth vigor of flax plants representing in the plant height, fresh and dry weights of shoot biomass is a strong evidence of the first assumption. The in vitro investigation of flax-yielded seeds strengthens the second vision. The results of that showed a significant decreasing in the seed germination percentage (7.44-42.26%) and seedling root (16.41-54.07%) and shoot (10.58-57.64%) growth of the two seeds selected for the investigation, including Portulaca oleracea L. and Echinochloa crus-galli L. Upon the results obtained and drawn conclusions, using such naturally sources of crop treatments either alone or in combination is hardly required not only for the best yield could be obtained, but also in term of continuous searching for more friendly and economically sounder agro-chemicals. We may, therefore, recommend riboflavin plus micronutrients at 50+1.5 mg L-1 as the best treatment could be chosen for the best results could be obtained over the two sides of action; combating weeds and increasing crop productivity.