Why do flowers bloom at different times of the year and what determines when they flower?

Answer 1

It's one of those lovely examples of evolution. Flowering plants have evolved to bloom at a time that is optimal for the propagation of the species. Some plants bloom continuously to optimize the chance of being pollinated. Some bloom very early or very late, so there's not a lot of competition. Some bloom in harmony with insects or other animals that serve as pollinators. So they bloom when there are lots of that particular insect or animal around to insure propagation. They have evolved over hundreds or thousands of years to optimize survival of the species. And, as it turns out, it's a beautiful thing.

Answer 2

Temperature does initiate blooming and seed production in some plants. However, day length, or really night length, seems to play a more important role in blooming than does temperature. Poinsettia is the most common and well -known example of this phenomenon. Cold weather would just kill a poinsettia. But it "knows" to bloom at Christmas because the nights are so much longer than the days in the late fall (October-November northern hemisphere). The poinsettia is so sensitive to having a long night of solid darkness that car headlights shining through the corner of a greenhouse on a busy street corner, or a nightguard's flashlight beam, will cause the plants on which they shine to never bloom that Christmas.
Crape Myrtles are the opposite. They never bloom until the nights get short.
An example of a plant that "doesn't care" is the pansy. Pansies are useful for season-long color in mild winter climates because they bloom regardless of night length. Too hot or too cold will slow down flower production, however.

Answer 3

The process to which your question refers is called photoperiodism. How day length affects the flowering of some, but not all plants

Around 1920 Garner and Allard, working on tobacco plants at an USDA experimental station, discovered some very large plants with enormous leaves among a batch of seed they were raising.


They looked forward to collecting the seed with a view to developing a strain. However, whilst the normal tobacco plants set seed in late summer, the large form showed no sign of flowering.

They therefore dug them up and transferred them to a greenhouse, where the plants eventually flowered in late December. The progeny of these plants exhibited the same characteristic of late flowering.


Garner and Allard experimented moving the plants from a darkhouse to a greenhouse on a daily basis and determined that these plants flowered with the combination of 9 hours daylight and 15 hours darkness, which is characteristic for Maryland’s latitude in late December.


At this point one should remember that latitude governs difference in day length. At the equator days and nights are of an equal length. The further one gets from the equator, the greater the difference in daylength.


Garner and Allard later determined that soya likewise flowers after exposure to a certain number of consecutive short days. Spinach and most cereals, however, responded to long days. Whilst some other plants, like tomato, are unaffected by day length and flower once they have reached a certain size or developed a particular number of leaves.


They named this response of plants to relative lengths of day and night photoperiodism, and classified plants as short-day, long-day and day-neutral.


It has subsequently been shown that plants do not measure daylength but night length. Thus short day plants can be inhibited from flowering by administering a brief flash of light during the night. Although the plants are measuring night length rather than daylight, the term photoperiodism has been retained.



The extent to which plants can determine precise daylengths is extraordinary.
Some genera can perceive a difference of between 2-5 minutes. Likewise the number of consecutive days of a particular length can be as low as 1-4.


The change that occurs as a result of these daylengths being reached, is the shoot tip changes from normal vegetative growth, to producing a flowering bud.


The daylength at which the change from vegetative to flowering state occurs is known as the critical photoperiod.


Note that

short-day plants initiate flowerbuds when the daylength is less than the critical period

long-day plants initiate flower buds when the daylength is greater than the critical period.

It is not the absolute length of day which is important in determining whether a plant is short or long day.

A long-day plant flowering in early spring (black henbane) will have a critical period several hours shorter than a short-day plant flowering just after mid-summer (cocklebur).

Answer 4

It's A genetic thing..some are cold wether flowers and some warm weather..some seeds wont even germinate or sprout when too warm of wether and vice versa..the temperature drop/and/or /raise determines when they bloom