Thalictrum aquilegifolium L. ‘Black Stockings,’ with its interesting foliage, is used as a cut greenery. We tested the postharvest longevity of the foliage after different 24-hr conditioning treatments with nanosilver (0, 5, 10, 15, 20 mg dm−3) and 20 g dm−3 sucrose and compared the results with those obtained using the standard preservative (200 mg dm−3 8-hydroxyquinoline citrate + 20 g dm−3 sucrose) and Floralife 200 Clear. The longevity of the foliage and the content of assimilative pigments were evaluated and the functioning of the photosynthetic apparatus (F0, Fm, Fv/Fm) was analyzed. We found that leaf senescence, as determined by chlorophyll a and carotenoid content after 14 days of holding, was most effectively inhibited by the solution containing 5 mg dm−3 nanosilver and sucrose. This solution increased the maximal quantum efficiency of photosystem II (Fv/Fm) in the leaves.