MadSci Network: Botany |
The phenomenon of trees and shrubs blooming abnormally early during a warm period in winter is different than photoperiod requirements for flowering because the flower buds are already formed. Most of the species that bloom early are nonnatives that have not evolved in the climate they are now being grown in. Native species are unlikely to bloom during a warm period in winter because they evolved a requirement for a longer period of cold temperatures to satisfy dormancy. The abnormally early blooming is due to people meddling with nature and planting nonnative species in climates different from where they evolved. Flowering is a complex process often determined to some extent by both photoperiod, or daylength, and temperature. For example, poinsettia requires photoperiods below about 12 hours to produce flowers. However, at low enough temperatures, flowering in poinsettia requires long photoperiods. In Canterbury bell (Campanula medium) flowering is promoted by cold temperatures alone or by short photoperiods alone. Spring flower bulbs (daffodil, tulip, hyacinth) require several weeks of cold temperatures before they can flower. Other factors can influence flowering such as mineral nutrition, plant maturity and plant carbohydrate reserves. Photoperiod is also an important signal in determining when many trees go dormant in the fall. For example, dogwood (Cornus florida) normally goes dormant in the fall due to short photoperiods. If placed in a warm greenhouse, it will still go dormant with short photoperiods, but not if the photoperiods are long. With long photoperiods and warm temperatures it will continue to grow. References Will early winter blooms bring a withering spring? Foreign flowers may be fooled, but the natives know better Regulation of Flowering in Canterbury bell by Both Photoperiod and Vernalization Salisbury, F.B and Ross, C.W. 1985. Plant Physiology. Belmont, CA: Wadsworth. Re: What determines when the flowers of plants appear on the plants?
Try the links in the MadSci Library for more information on Botany.