Why Do Flowers Close Up At Night?

One of the most interesting things about plants is their individual quirks, which look strange at the first glance, but actually demonstrate how clever these plants can be. 

One such trait is the way that certain flowers close up at night.

Have you ever wondered why they do it? Time to find out.

Why Do Plants Adapt?

All plants have adapted over generations in order to become better equipped to survive their environments.

This ensures the plant’s survival long enough to reproduce and to continue the species onto the next generation.

For example, many plants have adapted to contain poisonous alkaloids to stop animals from eating the foliage and depriving the plant of the ability to photosynthesize.

Others have formed spikes on their foliage, or in the case of jewel orchids, have adapted their leaves to be invisible on the forest floor to animals that might want to eat them.

Many plants also change their behavior according to the time of day.

If you’ve ever seen a time-lapse of a calathea houseplant, or you grow one yourself, you’ll know that the leaves move with the direction of the light, closing up completely when it gets dark.

Flowers do this, too. On some species, the flowers will turn to face the sun, and close up at night, or even when the sun goes behind a cloud. 

Both leaves and flowers closing up can be worrying, especially if a plant does both at once. You might be concerned that you’ve killed your plant, but don’t worry. 

Your plant is simply doing its thing. But why are they doing it, exactly?

How Do Plants Sleep?

In some plants, their flowers unfurl during the day, and close again at night, and in others, the reverse is true.

These plants adapt to changes in light and in temperature, which indicate the time. This particular trait is called nyctinasty. 

While this sounds like a mouthful, it’s a combination of two different Greek words, translating as ‘night’ and ‘pressed down’, or pressure.

This controls how and when the plant moves, corresponding with temperature fluctuations, and the day–to-night light cycle. 

If you’ve ever grown the annual Mimosa pudica, (see also Everything You Should Know ABout Mimosa) also known as the sensitive houseplant, you’ll be familiar with this. If you ran a finger over a leaf, it would curl up, away from your touch. 

This is a subtype of nyctinasty, and reacts to vibration or touch, also known as seismonasty.

Nyctinasty acts as a clock for the plant, creating a sort of circadian rhythm similar to the one that’s programmed in us. 

While plants don’t have their ‘body clock’ within a nervous system, they still follow a day and night pattern which is dictated by light and temperature, and as they get older, this rhythm gets less efficient.

For some plants, their foliage and flowers stay open no matter the time. In others, some only open for the warmest part of the day, and for some, they reserve their beauty for the night.

Day Flowering Plants vs. Night Flowering Plants

Plants That Flower During The Day

Flowers that open up during the day and close during the night are also called day bloomers.

Some people refer to how they close up at night or in rainy conditions as ‘going to bed’, as the plants unfurl again in the morning or in better weather.

Some people also look at their day bloomers to know when it’s time to pack up their gardening tools, as when the likes of osteospermum and other flowers close up on a cloudy day, there’s a good chance of rain!

Day blooming plants include tulips, gazania, crocuses, mesembryanthemums, oxalis triangularis, sunflowers, and morning glory.

Plants That Flower Exclusively At Night

Some plants only bloom when the sun goes down, often lasting into the early morning of the following day. 

These flowers are exclusively pollinated by those animals and insects which are active at night, such as fireflies, moths, bats, bees, mice, and lizards. 

Some of the most fantastic flowers only open at night, and some only create their dramatic displays for a single evening.

The possibilities are endless with these plants, and while day-blooming flowers are gorgeous, night-blooming flowers are on another level entirely.

Epiphyllum is perhaps the most well-known night flowering cactus, (see also Everything You Should Know About Epiphyllum) known for its orchid-like flowers. Other night flowers include night blooming jasmine, night phlox, some wisteria, evening primrose, night gladiolus, and datura. 

How Do Some Plants Close Up Their Flowers At Night?

How plants close up their flowers for the night is more understood than why they do it.

It depends on the plant as to how they do it.

In plants which close up their foliage, the mechanism lies with the pulvinus, which acts as a joint at the base of a plant leaf.

The movement comes about when the turgor pressure changes, either opening the leaf outward, or closing it completely. 

Other plants have additional cells on the outside of the base of the flower, and on the inside, too. These cells either force the flower to open, or to close it completely.

Some plants grow upper and lower petals at different rates, which helps them to close the flower when they need to. 

Other species can take the water out of the cells contained in the base of the petals, contracting them and forcing the flower to close.

Why Do Flowers Close Up At Night?

There are quite a few theories which try to explain why some flowers close up at night, and while all of them are plausible, we don’t know which ones are right for which plants, not for certain.

Some suggest that flowers close up at night to protect the blooms against freezing temperatures, which could kill them before the plant has a chance to reproduce.

Others think that this eliminates the risk of the flower’s pollen getting wet either in rain or in dew, as it can become too heavy to carry for pollinators, and sometimes it can stop doing its job entirely.

An additional theory is that the flowers save their energy and pollen for those pollinators which are only active during the day, keeping out unwanted pollinators or pests at night.

Others believe that some flowers close in order for predators to spot flower-eating prey such as mice from afar, protecting the plant from being eaten.

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