2019 ASHS Annual Conference

Herbaceous peonies (Paeonia lactiflora Pall.) are common perennials used both in gardens and landscape as well as cut flowers. Peonies require a chilling period for dormancy release and flowering. Gibberellic acid (GA₃) can partially replace the chilling requirement. The objective of this study was to evaluate GA₃ effects on peony bud differentiation and development during controlled chilling and early forcing, as well as growth and flowering. Two peony cultivars, ‘Sarah Bernhardt’ and ‘Inspecteur Lavergne’, 3-5 eyed crowns from Holland were potted in 3.8-L pots in mid November, allowed to root for 5 weeks, then placed in a 5°C cooler for 4 weeks. GA₃ (Florgib, Fine Americas) was applied as a 100 mg/L drench (250 ml/pot) just before or immediately after chilling. Bud differentiation and development was monitored using stereomicroscope at potting, after rooting (before chilling), after 1, 2, 3 or 4 weeks of chilling, and at 5, 10 or 15 days after chilling. All buds were removed from the sample plants, measured, and dissected under a stereomicroscope to assess development. Root dry weights and crown dry weights were also determined after rooting, after chilling, and 15 days after chilling. Ten plants of each treatment were grown in the VT greenhouse F4 after chilling until flowering. Data indicate that plants treated with GA₃ prior to chilling had a greater number of buds that were also larger and in higher differentiation stages than did untreated plants. For plants grown in greenhouse, GA₃ treatments prior to chilling shortened the days to emergence by 7 days and shortened the days to cracking color by 15 days with ‘Sarah Bernhardt’. GA₃ treatments (both before and after chilling) shortened the days to emergence and cracking color by 14 to 15 days with ‘Inspecteur Lavergne’. GA₃ treatment prior to chilling increased the number of shoots with both cultivars and GA₃ applied after chilling increased the number of flowers with ‘Inspecteur Lavergne’.