Growth and Morphology of Seven Indoor Foliage Plants in Response to Day Length

Most plants used as indoor foliage or for interiorscaping are slow growing and of tropical origin, where daylength changes little throughout the year. Limited research has been conducted to determine if daylength can be used to promote desirable morphological growth responses of commercially important genera in controlled environments. Therefore, we investigated how Callisia repens ‘Pink Panther’ (pink panther plant), Fittonia albivenis ‘Mont Blanc’ (nerve plant), Peperomia obtusifolia ‘Citrus Twist’ (baby rubber plant), Pilea cadierei ‘Ellen’ (silver plated pilea), Pilea depressa ‘Sao Paulo’ (baby toes), Pilea glauca ‘Mystifall’ (silver sparkles pilea), and Pilea peperomioides (Chinese money plant) responded to a range of daylengths. Vegetative shoot-tip cuttings were rooted and subsequently grown under photoperiods ranging from 9 to 16 hours in a greenhouse with average daily temperature (day/night) and daily light integral set points of 20 °C (23/17 °C) and 7 mol·m −2 ·d −1 , respectively. Plant height, stem diameter, leaf number, leaf area, and shoot dry mass (SDM) were recorded at harvest. Species responded differently in their morphological responses to daylength. Although nerve plant, baby rubber plant, and baby toes exhibited minimal variation in morphological traits, indicating relative insensitivity to daylength, morphological responses were observed in pink panther plant, silver plated pilea, silver sparkles pilea, and Chinese money plant. For instance, the plant height and SDM of the Chinese money plant increased by 259% and 58%, respectively, as daylength increased from 9 to 16 hours. Conversely, silver plated pilea developed fewer and smaller leaves and a lower SDM under long daylengths. Shoot biomass partitioning in Chinese money plant shifted from leaves to stems with daylength increasing from 9 to 16 hours. These findings suggest that extended daylengths enhance vegetative growth in some species while inhibiting it in others, and that morphological responses are species specific. This highlights the importance of species-specific photoperiodic lighting strategies in commercial foliage plant production.