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Do flowers bloom WHILE it's raining? Or do they need sun and light for blooms to open? There are lots of info on what they need to bloom, but not what conditions they actually bloom under. Daylight? Darkness? Rain? Sun? Warmth? Cold? What are the scientific conditions for an actual blossom to emerge?
Question Date: 2020-05-22
Answer 1:

Flowers are all different, and blooming is not an instantaneous event, so it is impossible to give one set of "scientific" conditions for when blossoms emerge. In most plants, the flowers open when enough force builds up to rupture the connections between adjacent sepals. (The sepals comprise the green "casing" of the bud and protect the flower before it opens.) This force accumulates due to cells in different locations expanding by varying amounts. In some plants, this expansion is simply caused as cells grow at varying rates (or in some cases cells selectively dying). In others, cells in the buds accumulate water or ions which causes swelling. Once the cells have expanded/grown/swelled enough, the flower opens. This means that, to some extent, flowers open simply "whenever they open". In most cases, opening is regulated by light intensity and duration, with some effect of humidity. However, because weather is not constant, the prevailing conditions at the exact moment a flower is considered "open" cannot be predicted precisely. Also realize that some flowers open and close repeatedly , with a rhythm that may be dictated by weather, time of day, or internal chemicals rather than external stimuli (so the environment of such a plant could be changed but it would continue to open and close regularly.) This has been known for hundreds of years and is the basis for so-called "Flower Clock Gardens". In addition, some flowers will close in anticipation of rainfall. The reasons for repeated opening and closing are not fully understood, but generally are thought to protect the pollen in the flower for times when pollinators are active and help the plant reproduce (e.g., closing or turning down during rain to prevent pollen from being washed away.)

An interesting tangent, the bunchberry dogwood is the record holder for fastest flower motion, opening in less than 1 one-thousandth of a second.

Answer 2:

Hi Lauren, thanks for such a great question! You may be having a hard time finding these answers because flowering conditions vary quite a bit! Ultimately, a flower contains the plant's reproductive organs and its job is to get fertilized and create a seed. Some plants just need to be big and healthy enough to have the extra energy to create a flower, but many have to time their flowers very carefully to ensure their success.

For example, some flowers are able to self-pollinate, so they don't have to rely on pollinators to get the job done; so long as they have enough energy, they could probably make flowers any time of year. However, many plants are not able to self-pollinate and rely on pollinators to carry their pollen to other individuals.

Because insects are often inactive in winter, these plants need to be sure that their flowers emerge at the same time that the insects are becoming active. They may keep track of this using the typical seasonal markers, such as the length of the day (photoperiod), temperature, or even precipitation.

Some flowers use pollinators which are active during the day, like bees or hummingbirds, but some use pollinators that are active at night! Some desert plants use bats and moths as pollinators, so they only open their flowers at night. Because each plant has different needs, and the environments they occupy vary so much, there is no single answer for when a plant produces a blossom. But if you look at research a certain plant species, those questions may have been answered!

All the best,

Answer 3:

Good question. The answer depends on what kind of pollinators the flowers attract. Flowers are a way for plants to get pollinators to visit. If the pollinators the plant uses are bats, the flowers probably open at night and are white, so they are more visible. These flowers may close during the day. This avoids having other pollinators visit. Plants that use hummingbird pollinators would be open during the day, but they may close at night. Morning glories, are an example of plants that use pollinators like hummingbirds and insects. They close when the day gets warmer. Other flowers might not close at all.

Keep in mind that the plants don't know why they are opening or closing. But plants with genes that make them open at the best time leave more offspring.

How else do you think plants attract pollinators?

Thanks for asking,

Answer 4:

Good question! On a molecular level, there are genes within the plant that are activated to create proteins to make a flower grow in exactly the “right conditions.” The problem, as you’ve intuited, is that these conditions are totally dependent on the species of flower.

Like you said, there are a lot of environmental factors that determine when a flower might bloom (like rain, sun, light, temperature). The different ways this drives flower blooms depends on the flower - rain lilies will only bloom after a heavy rain, while wildflowers bloom following a big rain from spring to summer. Some plants bloom every year (like poppies), while others only bloom once every few years (like yucca).

It’s hard to pinpoint the specific conditions for a blossom to emerge as you’ve asked, mostly because of all of these different environmental conditions. However, you can think of a flower blooming as a sign to a pollinator (like a bee or moth) that they are ready to reproduce. This show depends on the behavior of the pollinator - flowers take a lot of energy to grow, and it’s a waste if a plant invests that time and effort into making a flower if a bee won’t be around to pollinate it. Therefore, flowering times have to be perfectly synced up with the behavior of the pollinator.

The study of plant flowering is called “phenology” - there’s a whole network of scientists dedicated to asking questions exactly like yours! The problem we’re facing now is with climate change; if flowers bloom too early because it’s warmer earlier in the spring, they’ll die before pollinators are able to reach them, and won’t be able to reproduce.

Answer 5:

Plants need sunlight in order to get energy, but in order to grow they also need materials with which to actually grow.

Some of these materials come from the soil, while others come from the air. They get the materials out of the soil by dissolving them in water and then carrying the water up through the plant. This is why plants need water. Opening themselves up to get air as well causes them to lose water, so they need more water.

Thus, plants will need both water and light in order to grow. They don't care whether they get the water through rain or through water flowing into the soil from somewhere else, but they do need to get the water somehow.

Finally, the warmer the temperature is, the faster chemical reactions happen, and everything a plant does it does through chemical reactions, so warmth is also very useful. Water also does not flow if it is frozen, so plants need temperatures to be warm enough for the water to be water and not ice.

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