Plants respond to environmental cues such as temperature and photoperiod to flower when reproductive success is most likely. Producers and retailers of flowering plants require them to bloom for specific, predetermined dates when they can be marketed most successfully. Ornamental herbaceous perennials have posed some unique challenges to growers attempting to produce uniform crops in flower consistently. This has prompted research into the flowering requirements of a wide range of herbaceous perennials, revealing that vernalization and photoperiod can induce or hasten flowering and that seedlings of several species must complete a juvenile phase before they can respond to inductive conditions (Runkle et al., 2001).
Aquilegia includes ≈65 species, and extensive hybridization has yielded many cultivars of this popular spring-blooming perennial (Armitage, 1997; Whitman et al., 2003a). Vernalization is a cold treatment that induces or promotes flowering (Chouard, 1960) and flowering of Aquilegia is generally considered to require vernalization, although this requirement varies among cultivars (Finical, 1998; Weiler and Shedron, 1986; Whitman et al., 2003a, 2003b). No nonvernalized seedlings of ‘McKana’s Giant’, ‘Fairyland’, or ‘Crimson Star’ flowered within 7 months after sowing (Shedron and Weiler, 1982). Six weeks of cold was the minimum needed for complete flowering of populations of ‘Bluebird’, ‘Cardinal’, ‘Dove’, ‘Miniblue’, and ‘Robin’ (White et al., 1989). However, 50% of nonvernalized ‘McKana’s Giant’ seedlings flowered after 11 to 12 months in the greenhouse (Shedron and Weiler, 1982). In separate studies, all noncooled A. flabellata ‘Cameo Blue and White’ seedlings flowered an average of 38 d after transplant (Finical, 1998) and 90% of noncooled ‘Remembrance’ flowered, although time to flower was not presented (Niu et al., 2002). Although some nonvernalized plants bloom, vernalization often significantly hastens flowering as reported in four cultivars of A. flabellata and four interspecific hybrid cultivars (Garner and Armitage, 1998), five selections of Aquilegia (Finical, 1998), and ‘McKana’s Giant’ (Shedron and Weiler, 1982).
Vernalization is effective when Aquilegia seedlings have passed the juvenile stage, which occurred at 12 to 15 leaves in ‘McKana’s Giant’, ‘Fairyland’, and ‘Crimson Star’ (Shedron and Weiler, 1982) and selected hybrids in the ‘Swan’, ‘Music’, and ‘Songbird’ series (Whitman et al., 2003b). Once plants were mature, the vernalization requirement varied among cultivars and was reported as 10, 4, and 8 weeks for ‘McKana’s Giant’, ‘Fairyland’, and ‘Crimson Star’, respectively (Shedron and Weiler, 1982). Cultivars in the ‘Swan’ series flowered after only 3 weeks of cold (Whitman et al., 2003b). After vernalization, photoperiod has little or no effect on flowering of Aquilegia (Shedron and Weiler, 1982; Weiler and Shedron, 1986). To simplify production and improve performance in warmer climates, plant breeders have developed Aquilegia cultivars with reduced vernalization requirements (Merritt et al., 1997). In 2002, the Aquilegia ‘Origami’ series was released (Thomas and White, 2002) with a reported vernalization requirement of 14 to 21 d at 5 to 10 °C (Syngenta Flowers, n.d.). Kieft-Pro-Seeds developed ‘Winky Double Red and White’ (Burns et al., 2003); however, little information on flowering requirements was available. Our objective was to test these cultivars for juvenility and vernalization responses so that populations of plants could be commercially produced in flower in a complete and predictable manner.
Armitage, A. 1997 Herbaceous perennial plants. Stipes Publishing, Champaign, IL
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Finical, L.M. 1998 The effects of plant age, photoperiod, vernalization, and temperature on the growth and development of Aquilegia and Gaura. MS thesis, Dept. of Horticulture, Michigan State Univ., East Lansing, MI
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Niu, G., Heins, R., Cameron, A. & Carlson, W. 2002 Prevernalization daily light integral and vernalization temperature influences flowering of herbaceous perennials HortScience 37 1028 1031
Padhye, S.R. 2006 The influence of vernalization on flowering of Campanula ‘Birch Hybrid’ and Dianthus gratianopolitanus ‘Bath’s Pink’ and the regulation of flowering of Coreopsis grandiflora ‘Sunray’ by vernalization, photoperiod and light quantity. PhD diss., Dept. of Horticulture, Michigan State Univ., East Lansing, MI
Syngenta Flowers (n.d.) Aquilegia Origami™. 17 Feb. 2012. <http://www.syngentaflowers.com/country/us/en/seeds/GrowingGuidelinesLib/aquilegia.pdf>
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