Introduction Conservation measures, along with the basic in situ conservation strategy for vulnerable species, are signifi cantly oriented towards micropropagation, and, particularly, their in vitro programming. This plant material propagating technique has many advantages and can signifi cantly advance conservation of plants. For in vitro conservation, slow growth of developed plantlets is used, which results in a prolonged duration of the two subcultures [1]. The objective of our research is establishing the conditions limiting the growth rhythm while improving the survival rate of plantlets, and supervising their development. Material and methods The objects of the research under discussion are rare spontaneous fl ora species from Moldova which have a known ornamental value. These species are Lilium martagon, Fritillaria montana, and Bellevalia sarmatica [2]. The biotechnological research methodology has been based upon the general methods involving classical cultures of isolated tissues and plant organs [3]. Neoplantlets obtained according to the protocols described above [5,6] were transferred to the MS basic medium (Murashige and Skoog, 1962), without using any plant hormones, while various concentrations of sucrose such as 20, 30, 60, 90, and 100 g/l were applied. Results and discussions It is known that increasing the concentration of sucrose as a source of carbon can speed up the growth of plantlets [3], yet a certain amount of sucrose in the environment can be used as an additive which inhibits the growth of plantlets [4]. After 12 months of cultivation, the amount of regenerated plants which survived was assessed, and their visual analysis was performed. At the average concentration of sucrose of 20-60 g/l, a greater number of plantlets were necrotized because of vitrifi cation. At the maximum concentrations of sucrose (90, 100 g/l), the development of the plantlets apparently stopped, and the inoculation size remained unchanged. This environment had the highest percentage of viable plants. Conclusions Therefore, to maintain Lilium martagon L. as a species in vitro for a long term, after the propagation phase, bulbs can be transferred to MS-100% environment supplemented with sucrose concentration of 100 g/l. To maintain Fritillaria montana and Bellevalia sarmatica as a species, according to the viability estimates, the most optimal environment is MS-100% with sucrose in an amount of 90 g/l. Hence, higher sucrose concentrations in nutrient environments can be used successfully for in vitro long-term maintenance of rare species.