The presence of hybrid and exotic poplar plantations is considered to pose a severe potential threat to the native populations of Populus nigra in Western Europe. To evaluate the potential risks associated with the use of exotic or hybrid poplar plantations, particularly plantations of P. canadensis and P. nigra cv. italica [ P. nigra var. italica ] (Lombardy poplar), in the surroundings of natural P. nigra stands, the flower biology of a collection of P. nigra , P. canadensis and P. nigra cv. italica, was assessed. The results of this study showed that, in this stand and over the two years of observation, the flowering time did not constitute a barrier to hybridization between P. nigra and P. canadensis . In contrast, it appears that during both springs, P. nigra cv. italica could not hybridize with native female black poplars and female P. canadensis trees in the stand, due to non-synchrony of flowering.