Effects of Intermittent Low-temperature Storage Duration and Cycle on the Bolting and Flowering of <i>Delphinium elatum</i> in Summer

Early-bolting in summer is a major problem when growing delphinium seedlings in summer to produce cut flowers that will be shipped in autumn and winter. In this study, an intermittent low-temperature storage (ILTS) treatment that induces flower bud differentiation in strawberry and prevents rosette formation in Eustoma significantly increased the Delphinium elatum cut flower length. Moreover, ILTS was as effective as growing seedlings under cool conditions at preventing early-bolting. We analyzed the effects of six ILTS treatments that differed regarding the treatment temperature (5 and 10°C) and treatment cycle (3 days/3 days, 6 days/6 days, and 12 days/12 days; ambient conditions/cool and dark). Cut flowers were significantly longer with the 6 days/6 days treatment at 10°C than for the control treatment. Furthermore, repeating the ILTS treatment cycle (6 days ambient conditions/6 days at 10°C) a total of four times produced high-quality cut flowers regardless of the cultivar. Therefore, this ILTS treatment may be ideal for preventing early-bolting in D. elatum.