Light Spectra Have Minimal Effects on Rooting and Vegetative Growth Responses of Clonal Cannabis Cuttings

Until recently, most clonal cannabis ( Cannabis sativa ) has been propagated using fluorescent lights. Transitioning to light-emitting diodes (LEDs) may be a viable alternative lighting, enabling cultivators provide specific spectrum treatments enhance rooting while also saving energy. Vegetative stem cuttings of ‘Gelato-27’, ‘Grace’, and ‘Meridian’ were rooted for 15 days under various combinations blue (B), red (R), ultraviolet-A (UVA) LEDs, phosphor-converted white (W) (F) control treatment, each with canopy-level photosynthetic photon flux density (PPFD) 200 µmol·m −2 ·s −1 16-hour photoperiod. The ratios (B; 400–500 nm) (R; 600–700 narrowband LED treatment (1) BR, fixed B15:R85; (2) B, B75:R25 on day 0–2 followed by B15:R85 2–14; (3) B+UVA, 2–14 plus UVA 7–14; (4) B50, 0–7 B50:R50 7–14. W F both had static spectra. After the propagation period (i.e., plug stage), portion × cultivar combination destructively harvested remainder transplanted grown vegetatively an additional 21 transplant stage) PPFD ≈275 from ceramic metal halide fixtures then harvested. Although there no effects percentage that rooted, root index values higher in B+UVA vs. F. Further, relative dry weights plugs than treatment. At end stage, chlorophyll content index, B thicker stems compared BR treatments, exhibited lowest new aboveground growth. None aforementioned stage persisted post-transplant. use LEDs is promising, energy-efficient lighting B-enhanced appear performance cuttings.