Ornithogalum sp. are ornamental geophytes in the Asparagaceae family. The inflorescence is a simple raceme consisting of several florets with six petals in two whorls (Huxley et al., 1992). Native to the Western Cape of South Africa, O. thyrsoides and O. dubium, commonly called star of bethlehem, were first introduced to the market as cut flowers. More recently, shorter-stemmed clones and cultivars of both species have been selected and are gaining popularity as potted flowering plants (Littlejohn and Blomerus, 1997, 2000; Luria et al., 2002; Reinten et al., 2011). In the U.S. market, potted geophytes used as winter-blooming house plants are especially in demand (Daly and Henry, 2009). To support the further commercialization of potted Ornithogalum, more information on preplant environmental conditions and greenhouse protocols is needed.
Determination of proper temperature sequences for the entirety of bulb production and utilization is an important aspect of flower bulb horticulture. In the Ornithogalum production cycle, the first stage of bulb storage is the period immediately after bulb harvest and before shipping. The effects of temperature after lifting have been studied for a number of Ornithogalum species. Warm (25–30 °C) storage immediately after harvest promotes the ability of some species of Ornithogalum bulbs (Roh et al., 2007) to respond to later flower induction cues or bulb vernalization treatments, resulting in higher percentages of flowering or earlier flowering (Jansen van Vuuren, 1997; Jansen van Vuuren and Holtzhausen, 1992; Roh and Hong, 2007; Roh and Joung, 2004; Roh and Suh, 2008).
The second stage of bulb storage is the preplant storage phase when bulbs are subjected to cool temperatures before planting. Previous research indicated that preplant cool storage of Ornithogalum bulbs accelerated flowering. Roh and Hong (2007) recommended holding O. thyrsoides bulbs at 10 °C for 3 to 4 weeks or at 13 °C for 3 weeks to accelerate flowering and produce two or more inflorescences. Jansen van Vuuren and Holtzhausen (1992) reported that following 8 weeks of 25 °C storage after lifting, O. thyrsoides bulbs held at 5 °C for 6 weeks flowered earlier than bulbs held at 25 °C. With O. dubium, 3 weeks of dry storage at 13 °C resulted in significantly longer flower stems (taller plants) than treatments at 2, 9, and 25 °C (Luria et al., 2002). The duration of preplant cooling at 13 °C did not affect the time from planting to flowering, which was 20 ± 1 weeks. However, 13 °C for at least 2 weeks resulted in significantly longer flower stems compared with noncooled bulbs (Luria et al., 2002). De Hertogh and Gallitano (1997) reported that storing O. dubium bulbs at 9 °C for 4 weeks resulted in taller plants and decreased the number of inflorescences and days to flower compared with bulbs treated with 17 °C. They suggested that for potted plant production, bulbs should be stored at 17 °C for 4 weeks before planting. Suh et al. (2000) found that time from planting to flowering of O. dubium was reduced by 9 to 30 d when bulbs were stored at 10, 15, or 20 °C for 4 or 6 weeks compared with 25 °C controls. Contrary to the above studies, however, the number of flowers was significantly reduced and the inflorescences were shorter when bulbs were stored for 6 weeks at 10, 15, or 20 °C compared with the 25 °C control (Suh et al., 2000).
Cultural recommendations for Israeli-grown bulbs grown as container plants (Yodfat Revivim Horticulture, personal communication) suggest that holding bulbs for 3 weeks at 13 °C will speed flowering. However, we believe additional information will be helpful for growers to determine proper storage preplant temperature and duration for newly developed cultivars.
The floriculture industry must pay attention to the cost and profitability of production procedures (Miller, 2003). The average daily plant-growing temperature can be adjusted to speed up or slow down the development of a crop, but consideration must be given to whether the longer growing time at the cooler temperature greenhouse is actually more costly or not. With O. dubium, flowering was much faster under a 27/22 °C day/night temperature regime compared with 17/12 °C (Luria et al., 2002). Flowering of Ornithogalum arabicum and O. dubium was accelerated by 8 to 19 d, respectively, when plants were forced at 19/13 °C as compared with 13/10 °C (Suh et al., 2000). Warmer temperatures had no effect (O. arabicum) or slightly lengthened (O. dubium) inflorescences (Suh et al., 2000). Conversely, plants were shorter when grown at warmer temperatures (22/17, 27/22, and 32/27 °C) compared with 17/12 °C (Luria et al., 2002). Additional data on Ornithogalum response to growing temperature with named cultivars seems warranted.
The objective of this research was to expand the available information on preplant storage temperatures and durations and greenhouse forcing temperature on the growth and flowering of potted Ornithogalum.
Daly, M. & Henry, K. 2009 Evaluation of selected South African geophytes as winter-blooming houseplants for the Northern hemisphere Acta Hort. 813 37 44
Huxley, A., Griffiths, M. & Levy, M. 1992 Plant reproduction. In: The new Royal Horticulture Society dictionary of gardening. Macmillan, London, UK
Jansen van Vuuren, P.J. & Holtzhausen, L.C. 1992 The influence of temperature on phenological dating of Ornithogalum thyrsoides Jacq. as a commercial cut flower Acta Hort. 325 119 129
Lee, J.L., Gomez, M.I. & Miller, W.B. 2015 Paclobutrazol and flurprimidol control stem elongation of potted star of bethlehem HortTechnology 25 480 486
Littlejohn, G.M. & Blomerus, L.M. 1997 Evaluation of Ornithogalum genebank accessions for some characteristics of importance for breeding cut flowers or pot plants Genet. Resources Crop Evol. 44 227 234
Miller, W.B. 2003 Commercial flower production methodology. In: B. Thomas (ed.). Encyclopedia of Applied Plant Sciences. Elsevier Academic Press, New York, NY
Reinten, E.Y., Coetzee, J.H. & van Wyk, B.-E. 2011 The potential of South African indigenous plants for the international cut flower trade S. Afr. J. Bot. 77 934 946
Roh, M.S. & Hong, D.K. 2007 Inflorescence development and flowering of Ornithogalum thyrsoides hybrid as affected by temperature manipulation during bulb storage Sci. Hort. 113 60 69
Roh, M.S. & Joung, Y.H. 2004 Inflorescence development in an Ornithogalum dubium hybrid as influenced by bulb temperature treatments J. Hort. Sci. Biotechnol 79 576 581
Suh, J.-K., Lee, A.-K. & Lee, J. 2000 Flowering response of Ornithogalum as influenced by temperature and plant growth regulators treatment Acta Hort. 541 335 341