Due to the dynamic development of the floriculture market, new species and varieties of plants that can potentially be used as a source of cut greenery are constantly being sought. The experiment was conducted to analyze the effect of the cultivation site (unheated foil tunnel and open field) and treatments with the Pentakeep V formulation (0.00%, 0.02%, 0.04%, and 0.06%) on the vase life and postharvest quality of Polygonatum multiflorum ‘Variegatum’ cut foliage. There was a positive effect of the cultivation in the unheated foil tunnel on the vase life and biochemical parameters, namely the electrolyte leakage (EL), thiobarbituric acid reactive substances (TBARS), chlorophyll a + b (Chl. a + b), proline, peroxidase (POD), and ascorbate peroxidase (APX), of P. multiflorum cut foliage. Foliar application of Pentakeep V formulation at concentrations of 0.04% and 0.06% contributed to a decrease in the TBARS content in the P. multiflorum cut leaves, regardless of the plant cultivation site. Additionally, it reduced proline production in cut leaves of P. multiflorum cultivated in the unheated foil tunnel, which was confirmed by the analyses carried out after the 30 days of the experiment. Furthermore, the exogenous application of ALA during P. multiflorum cultivation inhibited POD activity, irrespective of its concentration and the site of plant cultivation.