Sideritis scardica is a short living perennial herb. This Balkan endemic grows in the higher parts of the mountains of Bulgaria, Albania, Greece, and Republic of North Macedonia. It is an endangered species and medicinally valuable plant. S. scardica has been successfully cultivated lately in Bulgaria and propagated by seed. This study presents preliminary in situ and ex situ data on the factors ... [Show full abstract] that control the seed production of S. scardica. Investigations were conducted in six study sites (three in situ and two ex situ) in the Rhodopes and one ex situ study site in the foothills of Pirin Mt in 2008 and 2019. The field experiments with enclosed flowers revealed that spontaneous self-pollination does not occur and insect pollen vectors are necessary. The pollinators of S. scardica were polylectic insects such as bumblebees (both in situ and ex situ) and honeybees (only on the big ex situ cultivated fields). Flowers were visited mostly for nectar as a reward and the pollen baskets were filled mainly by the pollen adhered on the pollinators’ body. The protection of wild populations of this plant species as well as its successful cultivation depends on the protection of its pollinators.