Photosynthetic Daily Light Integral Effects on Rooting and Vegetative Growth of Cuttings of Six Foliage Plants

Recently, millennials, social media, and the COVID-19 pandemic have spurred the demand for indoor foliage plants. Between 2019 and 2022, the wholesale value of foliage plants in the United States increased by 45% to $1 billion. However, few propagation protocols are available for greenhouse growers in temperate climates. Additionally, the mechanisms by which shade and succulent crops photosynthesize, root, and accumulate biomass in response to environmental parameters are largely unknown. Therefore, the objective of this study was to determine the photosynthetic daily light integral (DLI) that leads to uniform, high-quality, and rapid rooting of foliage crop cuttings. Vegetative shoot tip cuttings of Curio peregrinus ‘String of Thai Dolphins’ (dolphin plant), Curio rowleyanus ‘String of Pearls’ (string-of-pearls), Curio herreianus ‘String of Pearls Big Bead’ (string-of-pearls big bead), Peperomia obtusifolia ‘Emerald Isle’ (baby rubber plant), Peperomia ferreyrae ‘Happy Bean’ (pincushion peperomia), and Sedum makinoi ‘Tornado’ (stonecrop) were excised from stock plants. Then, the cuttings were inserted in plug trays filled with a propagation medium consisting of a 1:1 (v/v) of half 70% peatmoss, 21% perlite, and 9% vermiculite and half medium perlite. Then, the cuttings were placed under a DLI of approximately 5 mol·m −2 ·d −1 for 7 days of callus induction, and subsequently under shading of 70% (2.9–3.4 mol·m −2 ·d −1 ), 50% (4.5–6.5 mol·m −2 ·d −1 ), 30% (7.8–11.2 mol·m −2 ·d −1 ), or 0% (10.2–16.4 mol·m −2 ·d −1 ), resulting in DLIs ranging from 2.9 to 16.4 mol·m −2 ·d −1 . After 21 days, the stem length of stonecrop and pincushion peperomia rooted cuttings decreased as the DLI increased from 2.9 to 16.4 mol·m −2 ·d −1 . However, the stem length of string-of-pearls and string-of-pearls big beads rooted cuttings increased after 28 days as the DLI increased from 2.9 to 16.4 mol·m −2 ·d −1 . As the DLI increased from 2.9 to 16.4 mol·m −2 ·d −1 , the shoot dry mass of dolphin plant and baby rubber plant significantly increased by 168% and 189%, respectively. Additionally, the root dry mass of dolphin plant and baby rubber plant significantly increased by 376% and 50%, respectively. The quality index of all five cultivars was greatest under DLIs of 10.2 to 16.4 mol·m −2 ·d −1 , with the exception of pincushion peperomia, which had the highest quality index under DLIs of 2.9 to 4.6 mol·m −2 ·d −1 . Our findings indicate that higher DLIs benefit shoot growth during rooting, but not necessarily root biomass accumulation of all genera investigated.