The effects of supplementary lighting with high-pressure sodium (HSP) lamps alone or in combination with carbon dioxide (CO₂) on the growth, yield, and flower stem quality of two rose cultivars (“Loving Heart” and “Top Grace”) were studied. Compared to natural lighting (control), supplementary lighting alone was beneficial for plant growth, and it increased plant height, stem diameter, and the number of axillary shoots. Furthermore, increases in flower stem yield (>70 cm), flower stem diameter, fresh weight, and the number of petals per flower were also observed. The combination of supplementary lighting and CO₂ significantly enhanced all of the studied parameters compared to supplementary lighting alone. Moreover, stomatal density and chlorophyll fluorescence were seemingly affected by either supplementary lighting alone or in combination with CO₂. This is the first study to examine the beneficial effects of combined supplementary lighting and CO₂ conditions, and the resulting information is essential to rose growers and commercial production.