<p>Saffron is a geophyte grown in open field, but the possibility of year-round greenhouse cultivation is attracting increasing interest. We evaluated the application of supplemental lighting with white light emitting diodes (LEDs) in greenhouse conditions during the summer-winter period, in plants grown in pots on two benches, under two lighting treatments: natural light supplemented with LEDs (~ 260 µmol m^− 2 s^− 1) and natural light only (NL), which served as the control. LED lighting delayed flowering by almost a week (72 vs. 66 days after planting) but did not affect the mean number of flowers (4.2 flowers plant^− 1) or spice yield (29.9&#xa0;mg plant^− 1). However, LED lighting increased the phenolic acid content in the spice (+ 52%) compared with NL, indicating an improvement in spice quality. During the subsequent vegetative phase, net photosynthesis was increased by supplemental lighting, while plant leaf area was reduced, since lighted plants developed more leaves but with a lower specific leaf area compared to control. Notably, plants under LED lighting produced more corms (7.5 vs. 6.0 corms plant^− 1), with no differences in mean corm weight (3.4&#xa0;g plant^− 1) or starch content (645 mg g^− 1 corm dry weight) compared with NL, suggesting a potential for increasing the yield of propagative material. Overall, supplemental LED lighting may contribute to improving spice phytochemical quality and corm multiplication, which are both agronomically relevant traits for greenhouse soilless saffron cultivation.</p>