MadSci Network: Botany
Query:

Re: What is the 'trigger' for flowering?

Date: Tue Jan 9 17:48:16 2007
Posted By: David Hershey, Faculty, Botany, NA
Area of science: Botany
ID: 1167948091.Bt
Message:

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?


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