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FLOWER INITIATION
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We all enjoy flowers, but have you thought about how they are produced or initiated?

In another page we have considered
growth and development of an orchid plant, and the factors that are important in this process.  At a certain stage of a plants growth, it reaches a certain maturity where it is capable of producing flowers. Flower production, however, will not occur unless certain events trigger this process.  An understanding of these triggers can help ensure that you enjoy the beautiful flowers each year.

Flowering is initiated by one or more of the following factors:- 

  • Variations in day length
  • Temperature change
  • Rainfall variations, wilth changes to light levels

DAY LENGTH VARIATION

The daily variation in day length is a major cause of flower bud initiation.  Certain flowers are initiated by long day length, others by short day length.  The use of shading, or artificial timer controlled lighting, can, and is used commercially, to stimulate flowering out of normal flowering seasons.

As indicated in the following chart,  at the  equator, there is no seasonal variation in day length throughout the year.  As one migrates north or south,  seasonal variation in day length  increases significantly, to reach an extreme at the polar regions.  If you know a species is native of a higher latitude habitat, then you consider it probable that the day length will be a factor in initiating flowering.  This aspect is not confined just to orchids,  chrysanthemums and asters, for example are typical short day plants.  Calceolaria and scabiosa on the other hand are long day plants.  Within the Cattleya Alliance,  species of cattleya such as gigas,  warsceqiczii, trianaei and mossiae initiate their flowers during short days, whereas labiata initiates its flowers  during the longest days of the year.  Rebecca Tyson Northen in her excellent book 'Home Orchid Growing' discusses the use of controlling day length in the flowering of Cattleya labiata, and this chapter of her book is very interesting for those wishing to know more about this subject.

As can be seen below, at the equator there is no seasonal variation in day length throughout the year.  For equatorial plants, therefore, the other factors will be more significant in giving rist to flower bud initiation.

 

ChartObject Chart 1

Detailed tables of day length can be found in Charles and Margaret Baker's site at http://www.teleport.com/~cmbaker/COD/daylength.html

TEMPERATURES

Temperatures, both extremes and the diurnal variation, are important in bud initiation.  The temperature requirements of the main orchid habitats are discussed on the following pages

Orchid Habitats A discussion of the main orchid habitats of the world from the perspective of the characteristics of the monsoonal habitats of most orchids, and the differences with the non-monsoonal habitats of temperate areas such as New Zealand. The article is in a series of files - with the following links:-
HABITAT START PAGE - site layout, basic information;
ORCHID HABITATS Part 1 INTRODUCTION
ORCHID HABITATS Part 2; Habitat 1 TROPICAL LOWLANDS
ORCHID HABITATS Part 3 Habitat 2 MONSOONAL FORESTS
ORCHID HABITATS Part 4 Habitat 3 ARID RAIN SHADOW INLAND
ORCHID HABITATS Part 5 Habitat 4; HIGH ALTITUDE TROPICAL AND HIGH LATITUDE
ORCHID HABITATS Part 6 SUMMARY AND CONCLUSIONS
ORCHID HABITATS Appendix Paphiopedilum and cymbidium species habitat information These pages should be referred to for specific habitat information.

The average temperatures experienced by the main habitats are summarised below,  with a comparison made with a typical non monsoonal habitat (Wellington,  New Zealand).

ChartObject RAINFALL  ALL HABITATS

The seasonal variation should be noted.

In addition to the average temperatures, the diurnal variation (day to night variation) is also a very important characteristic of the various habitats.The Himalayan Cymbidium habitat is shown in the following graph. Note in particular the diurnal variation of 4 to 10 degrees celsius..

ChartObject TEMPERATURES                                   KALIMPONG NORTH INDIA

During the early summer period if cymbidiums do not receive a 5 to 8 degree Celsius diurnal temperature variation,  subsequent flowering will be inhibited.  In warm growing countries, some growers resort to the application of iced water during the summer to overcome high and stable temperatures which otherwise stops or reduces flowering.  Growing cymbidiums in an enclosed glasshoure, especially during the summer months, is a common reason for their non flowering.  This can also be a problem when growing under lights and in controlled conditions, where temperatures are not allowed to vary during the day.

SEASONAL RAINFALL

Rainfall is the third factor important in flower bud initiation.  Most orchids in common cultivation are from habitats subject to the summer monsoons with their marked seasonal onset and end.  For the main orchid habitats, the following indicates the monthly precipititation..  

ChartObject RAINFALL  ALL HABITATS
The very marked seasonality should be noted.  the Onset of the wet/dry season in  some instances is an important initiating factor.  

It should be noted that the habitats have significant cloud cover for much of the year, but especially during the summer, a period when in this country we have our brightest conditions. It is only the Foothill Mountain and Tropical High Altitude Habitats that are subjected to bright conditions, and this is only during the winter and spring. During the summers and early autumn all habitats receive many cloudy dull days. The differing pattern of rain and clear/dull days between the natural habitats for most of the orchids we grow, and what we naturally experience in this country, is something we all need to be aware of if we are to be successful in growing and flowering our orchids.  The relationship between the rainfall and light levels (clear skies) is something that we must recognise.

ChartObject CLEAR DAYS ALL HABITATS

For equatorial orchids, where there is little variation in day length during the year, the variations in rainfall (and associated light conditions) plays a very important part in the  flower initiation  process.  

CONCLUSION

The process of flower bud initiation can involve a number of factors, but I hope the above analysis will give information enabling aspects specific to a plant to be understood.  If you are having problems getting a plant to flower, find out all the information you can about the species involved, and then consider the above factors applying to that specimen.

Information on plants can be ascertained from the following sources, amongst others.

Orchid Habitats A discussion of the main orchid habitats of the world from the perspective of the characteristics of the monsoonal habitats of most orchids, and the differences with the non-monsoonal habitats of temperate areas such as New Zealand. The article is in a series of files - with the following links:-
HABITAT START PAGE - site layout, basic information;
ORCHID HABITATS Part 1 INTRODUCTION
ORCHID HABITATS Part 2; Habitat 1 TROPICAL LOWLANDS
ORCHID HABITATS Part 3 Habitat 2 MONSOONAL FORESTS
ORCHID HABITATS Part 4 Habitat 3 ARID RAIN SHADOW INLAND
ORCHID HABITATS Part 5 Habitat 4; HIGH ALTITUDE TROPICAL AND HIGH LATITUDE
ORCHID HABITATS Part 6 SUMMARY AND CONCLUSIONS
ORCHID HABITATS Appendix Paphiopedilum and cymbidium species habitat information

ALSO

      Encyclopaedia of Cultivated Orchids   by Alex Hawkes  -  extensive lists of species.  Now somewhat old, and some taxonomy is out of date, but it provides probably the most extensive information available
      The Manual of Cultivated Orchid Species
      by Bechtel, Cribb and Launert  -  an excellent modern book with extensive photographs.  Main species only listed for main genera
      What Orchid is That
       Edited by Alex Pridgeon Published 1992Extensive photographs and modern taxonomy but limited species lists
      Older books by Veitch  Manual of Orchidaceous Plants,  and B.S Williams The Orchid Growers Manual can also provide information.
      Genera specific monographs can also provide much useful information
      Publications such as the Orchid Digest have many habitat articles containing excellent information. .



 


Site established 9th May 1998