Abstract Ex situ collections of wild plants of conservation value are supposed to preserve the phenotypic variability of their wild source populations as well as their plastic responses to environmental stress. However, genetic erosion and adaptive evolutionary changes during cultivation are likely to impose strong constraints to those aims. To date, is it not known whether cultivation affects plant trait variability and stress response of species in botanic garden collections. We studied the effects of cultivation on the trait expression, genetic trait variability, and drought stress response in 12 plant species cultivated in Meise Botanic Garden, Belgium. We found that cultivation increased germination rate and leaf length across all species, while it decreased flowering and delayed the beginning of the flowering period in six drought-tolerant species. We furthermore found indications that plant response to drought was reduced by cultivation in some performance variables, while mortality due to drought slightly increased with cultivation. In three out of 10 traits measured, genetic variability decreased with increasing cultivation time in the botanic garden indicating a loss of evolutionary potential. Our results suggest that the preservation of the phenotypic status and evolutionary potential in ex situ collections is a challenging task and that the application of up-to-date protocols is decisive to achieve meaningful conservation collections.