To improve the ability to discriminate between Asiatic hybrid lilies (Lilium L.) with regard to cut flower longevity in breeding trials, sources creating nongenetic variation during the preharvest, harvest, or postharvest phases were identified. The bulb stock origin (grower) and evaluation temperature caused only small nongenetic variation in individual flower longevity. In contrast, the developmental stage of floral buds, when cut, produced significant nongenetic variation in flower longevity. This variation could be reduced by delaying harvest. An evaluation temperature of 17 °C was optimal to discriminate between longevity levels compared to 14 and 20 °C. Flower deformation due to withering of the petals was an improved criterion for the termination of flower longevity and was preferred instead of loss of turgor of the petals. Standard conditions for screening and selecting Asiatic hybrid lilies for individual flower longevity after cutting are proposed.