Ornamental plants comprise a great share of alien plant species worldwide. We studied invasion potential of perennial herbaceous ornamental plants in Finland by using their reproduction success as an indicator. Altogether, 220 clones from 166 species were included in the studies. In common gardens, 50% of the species were found to produce seedlings and 75% rhizomes, respectively. The species known for their invasion potential in temperate or cool climates appeared to be among the best seedling

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... roducers. In the field experiment, the highest seedling production (73%) was found in the semi-dry moisture regime, followed by the dry (40%) and the moist (27%) regimes. In the greenhouse experiment, 83% of the studied clones and 84% of the species emerged. Temperature sum required for the production of viable seeds for third of the studied species is reached at least every second year in latitudes 62–63° N. The results suggest several ornamental plants to have a potential for northward range expansion.