Selenium is a trace element which in small amounts is necessary for human and animal nutrition. In a living organism, it helps a number of antioxidant enzymes to function normally. In many parts of the world, including the Central European region, its content in agricultural products is very low. Attempts are therefore made to increase its content and cover human requirements with biologically valuable products by incorporating selenium into the system of plant nutrition. In a vegetation trial established in 2008 and 2009, we explored the effect of foliar applications of Se(IV) on yields and on its content in seeds and the uptake of selenium by a poppy (Papaver somniferum L.) stand. Selenium was applied at a rate of 300 g ha–1 during the stage of the end of elongation growth and after the fall of blossoms. Poppy yields were significantly influenced by the weather in the experimental years. In the dry year of 2009, poppy production was 40.6% lower than in 2008. Selenium application at the end of elongation growth reduced poppy seed yields by an average of 11.5%. Late supplementary nutrition at the stage after blossom fall also reduced yields (by 11.8%). Owing to the effect of extra-root Se nutrition, the content of selenium in poppy seeds increased highly significantly from 139 µg kg–1 to 757 µg kg–1 of seeds. Also the uptake of selenium by the poppy stand was significant and after foliar application it increased 4.8 times.