The increased horticultural interest in Helleborus requires the development of techniques for flowering control. Therefore, we have determined flower initiation and differentiation under natural conditions for Helleborus niger L and the hybrid Helleborus x ericsmithii B. Mathew. Once flower primordia were present in the underground buds of the plants, the effect of a cold treatment (336, 504 or 672 chilling units (CU)) and a supplemental gibberellic acid (GA(3)) application (500 mg L-1) on pre-cooled plants was examined. The cold treatment resulted in a progressive decrease of the time to flower. Moreover, when pre-cooled plants received a supplemental GA(3) application early flowering was further enhanced and these plants had a higher number of flowers with longer flower stems and larger flowers. (c) 2012 Elsevier B.V. All rights reserved.