High-pressure Sodium Lighting Affects Greenhouse Production of Vegetative Cuttings for Specialty Annuals

Abstract

The objective was to quantify the effect of supplemental lighting on cutting production for 10 herbaceous annual cultivars. Stock plants of four cultivars (Heliotropium arborescens `Atlantis', Petunia `Supertunia Sun Snow', Scaevola aemula `New Wonder', and Verbena `Tapien Soft Pink') received ambient light [average 6.2 mol·m-2·d-1 photosynthetic photon flux (PPF) during the photoperiod], or ambient light plus either 1.6 or 2.8 mol·m-2·d-1 PPF from high-pressure sodium (HPS) lamps for 11 hours. In a second experiment, the same four species plus six other cultivars were grown under ambient light (average 7.9 mol·m-2·d-1 PPF) or ambient plus 1.9 mol·m-2·d-1 PPF from HPS. The effect of HPS on the production of cuttings varied greatly between species. Growth of Heliotropium was not significantly affected by light level in either experiment. In the first experiment, the addition of 1.6 mol·m-2·d-1 PPF from HPS increased the number of Petunia `Supertunia Sun Snow', Scaevola, and Verbena cuttings by 14%, 51%, and 12%. The addition of 2.8 mol·m-2·d-1 PPF from HPS, increased cuttings harvested from these three species by 23%, 73%, and 22% respectively. In the second experiment, Petunia `Supertunia Sun Snow', Scaevola, Aloysia triphylla (lemon verbena), and Osteospermum `Lemon Symphony' had a positive cutting production response to HPS (17% to 45% increase), whereas cutting numbers of other species (Argyranthemum `Summer Melody', Lantana `Patriot Firewagon', Impatiens New Guinea hybrid `Pedro', Petunia `Supertunia Blue Wren', and Verbena) were not significantly affected by HPS. In both experiments, cutting quality (length, stem caliper, fresh mass, and dry mass) and subsequent rooting of cuttings were not significantly affected by light level.