Daylength Influences Time to Harvest and Stem Quality of Pycnosorus globosus and Caryopteris incana Specialty Cut Flowers

Abstract

As the demand for locally grown specialty cut flowers increases, cultivars of Pycnosorus globosus and Caryotperis incana are becoming more available for growers to produce as cuts. However, protocols for year-round greenhouse production are limited. Therefore, our objective was to determine if the photoperiod influences flower induction and development, time to harvest, yield, and morphology of billy buttons (Pycnosorus globosus) ‘Paintball Globe’ and ‘Paintball Poppy’ and bluebeard (Caryopteris incana) ‘Pagoda Lagoon’ and ‘Pagoda Dark Pink’ to facilitate commercial greenhouse production. Shoot-tip cuttings were rooted and transplanted into bulb crates and placed in a greenhouse with a mean daily air temperature of 20 °C and 9-, 10-, 11-, 12-, 13-, 14-, 15-, or 16-hour photoperiods or a 9-hour short day (SD) with a 4-hour night interruption (NI) from 2200 to 0200 HR for 11 weeks. Billy buttons initiated inflorescences and developed flowers under all daylengths; however, the greatest stem lengths were recorded under long days (LDs). Bluebeard inflorescences initiated under all daylengths were tested. Time to visible inflorescence and flower was hastened under daylengths ≤14 hours, whereas inflorescences under the 16-h photoperiod or 4-h NI never fully developed. For ‘Pagoda Lagoon’ and ‘Pagoda Dark Pink’, the critical daylengths for flower development were 14 hours and 15 hours, respectively. On average, only bluebeard ‘Pagoda Lagoon’ harvested under photoperiods ≥10 hours developed marketable stem lengths (>40 cm). To hasten time to visible inflorescence and harvest and ensure marketable stem lengths, billy buttons should be grown under daylengths ≥13 hours. Based on these results, we recommend growing bluebeard under a 16-hour photoperiod or NI for 4 to 6 weeks to promote vegetative growth, followed by an 11- to 14-hour photoperiod for flower induction and development. We classify billy buttons as a day-neutral plant for flower induction and a facultative LD plant for flower development. Similarly, bluebeard can be classified as a facultative SD plant for flower induction and an obligate SD plant for flower development.