How Plants Know When to Bloom: The Science of Flowering

Have you ever wondered how a cherry blossom knows it is spring?. How marigolds bloom only after the days get cool enough? How can plants possibly know it is time to bloom, when they lack eyes to see a brain to think or a mind to know?

Maybe nature is using magic? Wait… There is a science to this kind of magic!

Here are the secrets of how plants know to bloom!

1. Photoperiodism: The Key to Plants Knowing When its Blooming Season

The major clue to plants having a sense of when its blooming season is a phenomena called photoperiodism.

Photoperiodism is a plants ability to measure the length of the day/night. Surprisingly plants mostly measure darkness, not

Plants accomplish this trick” by using specialized proteins in their leaves called phytochromes.

These phytochromes basically act as eyes for the plant. When light hits the phytochromes during the day it causes a change in the phytochrome. At night the phytochrome slowly reverts back to its form. By measuring how much it has changed (or not changed, for nights) plants can approximate the length of the night and thus figure out what season it is.

Depending on how the night should be there are 3 types of plants:

Short-Day (Long-Night) Long-Day (Short-Night) and Day-Neutral Plants.

Short-Day plants bloom when the nights get longer ( in Autumn) (examples: Chrysanthemum and Poinsettia)
Long-Day plants bloom when their days get longer ( in late Spring) (examples: Spinach, Clover and Wheat)
Day-Neutrals bloom independent of the day/night length (examples: Tomato and Rose)

2. Thes Internal Clock: The Circadian Rhythm

Like humans plants have a clock. Unlike humans though the plants internal clock is controlled by genetics in its DNA.

The plants circadian rhythm works in tandem with its phytochrome to ensure that the plant doesn’t bloom at the time of year! So, if a plant thinks it is dark out (due to a night) but there is actually light shining on the plant the combination of the two will trigger a blooming response in the plant

3. “Florigen”: The Blooming Hormone

Once the leaves have sensed the time of year how does the plant tell the rest of its body to bloom?

Botanists have long theorized that there was some type of hormone that told plants to bloom. It wasn’t until recently that scientists discovered and even named the hormone!

The hormone is called Florigen. Scientists figured out what it did by figuring out what gene was responsible for causing plants to flower. This caused them to isolate a gene called FT (FLOWERING LOCUS T). They realized it was the gene responsible for creating a protein that told plants what time of year it was.

Here’s how it works:

The leaves sense the photoperiod (day/night length)
The gene for the FT protein gets activated
The FT protein gets sent to the shoot meristem (the tip of the stem) through the phloem
The Shoot Apical Meristem interprets the protein as a signal to bloom
The plants cells go into overdrive. Create flower buds instead of leaves

4. Vernalization: A Plants Memory

For some plants just sensing the photoperiod isn’t enough. For them it takes a winters nap in order for them to bloom. (These plants usually bloom in Spring or early Summer).

Scientists call this winters nap vernalization.

For these plants there is a gene that encodes for a protein called FLC (FLOWERING LOCUS C). The FLC protein acts as a brake on the flowering response. The plant doesn’t bloom in the Autumn, when its still warm.

When these plants spend the cold winter in dormancy the FLC gene gets turned off. Soon as Spring comes the plants cells will turn on the FT protein gene and it will bloom!

Why Timing is Everything

For a plant blooming out of sync with the seasons can be fatal! Blooming early, in the winter can cause the plant to waste its energy on flowers that will die in the winter frost. Blooming late in the Spring can prevent insects that pollinate the plant from finding it. By using these tools plants can bloom at the time of year and ensure their survival!

The Final Word

The time you see a plant bloom know that you are observing an amazing piece of biological machinery! Despite not having eyes to see or brains to think plants still use all their resources to make sure that they can reproduce! By using photoperiodism, their internal clock, vernalization and the florigen hormone plants can bloom at a time in order to survive.