Holland Technical Service Bulletin Number 31 was prepared for the WWW system by A.A. De Hertogh, L.B. Gallitano, M.E. Traer, and A.B. Russell, Department of Horticultural Science, NC State University. The information was obtained not only from original research conducted by the authors but also from databases released by other sources. This Bulletin was published by the International Flower Bulb Center (IBC), Hillegom, the Netherlands on behalf of the Dutch Flower Bulb Industry. Because of the various climates in North America and year-to-year variability of the weather, the IBC cannot and does not accept responsibility for divergent results that may arise using information obtained from this document or site. Photographs ©1997 by A.B. Russell and A.A. De Hertogh. Computer programming by Miguel Buendia, graphics by Brad Capel.