COLUMBUS, Ohio - Cool temperature treatments may be the key to the successful greenhouse production of osteospermums, native South African wild daisies that are gaining popularity in the United States as ornamental plants.
Ohio State University horticulturists have found that vernalization, a production technique of subjecting plants to low temperatures (between 32 and 45 degrees Fahrenheit), promoted and synchronized flowering, increased flowering times and reduced overall stem growth - characteristics that make for ideal floriculture crops.
"Our goal is to find crops that can be grown economically and fill a specific niche," said horticulturist Jim Metzger. "People get tired of the same cultivars. Introducing new species is just one of many ways the floriculture industry tries to increase diversity to keep up consumer interest."
The technique of vernalization eliminates the limitations of sporadic or non-flowering greenhouse growers were facing by relying on day length to control flower development. For many plants, day length dictates when and how much they flower.
"Osteospermum will flower without the cold requirement but it takes a long time and it's spotty. Growers want plants with full flowers that will bloom at the same time," said Metzger. "Looking at vernalization can improve the aesthetic characteristics of the plant, producing a product that is appealing to consumers."
Vernalization also provides growers with a product they can produce quicker and more cheaply. "If a greenhouse grower can increase the flowering time, then he or she can get the product shipped out quicker," said Metzger. "Vernalization also saves on energy costs because a grower is heating the greenhouse five degrees above freezing rather than to 65 or 70 degrees."
Osteospermum, although considered a weed in its native region, is becoming more popular in the United States as an ornamental plant because of its diversity in flower color, shape of the petals and foliage and its full display of flowers. "Many people really like osteospermum. It's got a lot of variety to it," said Metzger. "The plant produces striking flower colors that just seem to glow back at you. When you seen one in bloom, it just catches your eye."
Osteospermum is related to such plants as the Cape daisy, also a South African species, and the Freeway daisy, mainly grown in California. Osteospermum is marketed mainly as a potted houseplant or a landscape plant. Normally planted in mid-to-late spring, the annual plant will produce flowers that last through summer, as well as bloom again in the fall.