2019 ASHS Annual Conference

Cut flowers of Paeonia lactiflora Pall. (peony) hybrids, can be stored dry for multiple weeks between 0 and 1 °C. However, vase life and flower quality often decline following 4 or more weeks of storage. Cut peonies may be adaptable to sub-zero storage because stems and buds often experience freezing temperatures prior to harvest. To determine freeze tolerance of cut peonies: cut stems of three peony cultivars: Karl Rosenfield, Monsieur Jules Elie, and Sarah Bernhardt, were either left untreated or pulsed with water, 100 g·L^-1 sucrose, or 100 g·L^-1 fructose prior to holding stems at either 0, -2 or -4 °C for 4 h. Pulse treatments did not improve vase life of any cultivar. Sucrose-pulsed stems of ‘Karl Rosenfield’ and ‘Sarah Bernhardt’ had the lowest total vase life, a summation of the number of days in the bud or open flower stage. Pulsed and cold-treated stems of ‘Karl Rosenfield’ and ‘Monsieur Jules Elie’ opened 2 to 3 d and 0.5 to 1 d, respectively, earlier than untreated, control stems. Cold treatment did not affect bud opening or open vase life of ‘Sarah Bernhardt’. Freeze injury ratings were expressed as water-soaked spots on petals; stems and leaves were uninjured. Petals were not injured by freezing temperatures when stems were kept dry and not pulsed. Injury was greatest for all cultivars when stems were held at -4 °C. Fructose-pulsed stems of ‘Karl Rosenfield’ and ‘Monsieur Jules Elie’ had the highest injury ratings. Pulsing did not affect (P ≤ 0.1638) injury ratings on ‘Sarah Bernhardt’. An infrared camera was used to observe supercooling and multiple freeze events in stems, leaves, and buds held at -4 °C. Primarily, ice nucleation started at the base of the stems. Ice propagation then occurred throughout the stem, leaves, and bud within 1 to 2 minutes of initiation. Stems that were not pulsed remained in a supercooled state longer than those that were pulsed. These findings indicate that storage temperatures between 0 and -2 °C may be a valid option to extend cut peony availability.