The ongoing discovery of new aliens underscores the high level of propagule pressure today. Since 2005, 162 taxa (including additions from the current study) have been added to the list of Belgian neophytes. The origin of introduced diaspores and the routes they follow changes over time. Since the early 21st century the importation of Mediterranean container plants has strongly increased. Together with palm trees, olive trees, etc., large numbers of ‘stowaway’ weeds are being introduced. In 2008 we studied the weeds in containers of Mediterranean origin in garden centres. 120 identified species could be used in our analysis. 30 species are indigenous to Belgium, and all but 3 of these are also indigenous to Spain and/or Italy. The remaining 90 species are naturalized in Belgium (25 species), casuals (45), or are recorded for the first time (20). 29 of these 90 species (32%) entered Belgium from a secondary distribution range in Spain and/or Italy, not from their natural range. Our species list suggests that the recent increase of records for certain aliens in urban areas, although originally not identified as ‘container aliens’, is probably linked with the increased importation of Mediterranean container plants. It further shows that the interpretation of ‘lag time’ between initial introduction and invasive expansion requires an awareness of the continually changing processes that drive biological invasions as evolving against the background of an ever-shifting, unpredictable historical context. Each introduction presents a unique combination of species traits and human history.