Geranium and purple fountain grass leaf pigmentation is influenced by end-of-production supplemental lighting with red and blue light-emitting diodes

Under low-light greenhouse conditions, anthocyanin pigmentation in vegetative tissues of red- or purple-leafed floricultural crops is not fully expressed and, consequently, plants are not as visually appealing to consumers. Our objective was to quantify the effect of end-of-production (EOP; before shipping) supplemental lighting (SL) of different light sources, qualities, and intensities on foliage color of geranium (Pelargonium ×hortorum L.H. Bailey ‘Black Velvet’) and purple fountain grass [Pennisetum ×advena Wipff and Veldkamp (formerly known as Pennisetum setaceum Forsk. Chiov. ‘Rubrum’)]. Plants were finished under early (Expt. 1) and late (Expt. 2) seasonal greenhouse ambient solar light and provided with 16 hours of day-extension lighting from low-intensity light-emitting diode (LED) lamps [7: 11: 33: 49 blue: green: red: far-red light ratio (%); control] delivering 4.5 µmol·m^-2·s^-1, or 16 hours of EOP SL from highpressure sodium (HPS) lamps delivering 70 µmol·m^-2·s^-1, or LED arrays (100: 0, 87: 13, 50: 50, or 0: 100 red: blue) delivering 100 µmol·m^-2·s^-1, or 0: 100 red: blue LEDs delivering 25 or 50 µmol·m^-2·s^-1. Geranium and fountain grass chlorophyll content and leaf color were estimated using a SPAD-502 chlorophyll meter and Minolta tristimulus colorimeter, respectively. Relative chlorophyll content (RCC) and foliage L* (lightness), C* (chroma; a measure of saturation), and h° (hue angle; a measure of tone) values were significantly influenced by EOP SL and days of exposure. Generally, RCC of geranium and fountain grass increased from 3 to 14 days of exposure to EOP SL from HPS lamps and LEDs delivering 100 µmol·m^-2·s^-1. Under low daily light integrals (DLIs) [8.6 mol·m^-2·d^-1 (geranium) and 9.4 mol·m^-2·d^-1 (purple fountain grass)] EOP SL providing 100 µmol·m^-2·s^-1 of 100: 0, 87: 13, 50: 50, or 0: 100 red: blue light for ≥ 14 days resulted in lower L* (darker foliage), C* (saturated), and h° (orange to violet-red hues). Our data indicate that a minimum of 14 days of EOP SL providing 100 µmol·m^-2·s^-1 of 50: 50 or 0: 100 red: blue light enhanced foliage color of geranium and fountain grass leaves when plants were grown under a low greenhouse DLI ≤ 9 mol·m^-2·d^-1.