Why Does an Oxalis Plant Close at Night?

Oxalis are fascinating flowering plants famous for their low-maintenance care, abundant species, and iconic three-lobed leaves. However, oxalis plants also have the uncanny ability to close at night—a phenomenon that can be startling to new oxalis owners and exciting to experienced gardeners. But why do oxalis plants close at night, and is it normal?

An oxalis plant closes at night as a response to the lack of light. The process is known as nyctinasty and is a natural behavior for many plants. Nyctinasty is primarily a response to changes in light intensity, but low temperatures and similar conditions can also trigger this reaction.

It’s easy to mistake an oxalis that has closed at night for a sick plant, but you can rest easy as long as you’re taking good care of your plant. In this article, I’ll discuss how nyctinasty works in oxalis plants and answer some light response-related questions. Read on to learn all you need to know about nyctinasty and oxalis plants.

Definition and Significance of Nyctinasty

It’s common knowledge that oxalis plants enjoy moderate sunlight and dislike the harsh mid-afternoon sun. Plants left out in direct sunlight for too long usually have wilted leaves and die of overexposure. But very few people notice the plants are nyctinastic—even though most oxalis gardeners and carers realize the plant reacts to changes in light intensity.

Plants constantly react to external stimuli, but you probably never notice because the responses are so slow that it’ll take hours for effects to appear. However, some plants react to certain stimuli faster than others—like the oxalis plant and its nyctinastic light response.

Nyctinasty affects oxalis leaves and flowers in the same way as it does several other plants with the same response. One can best describe it as a “sleep movement” that causes leaves and flowers to bend, fold, or close up completely—depending on the oxalis species and light intensity at night.

Now, what exactly makes the oxalis plant react to light in such a manner? Is it magic, fairies, or perhaps some great apocalypse? It’s actually because of a somewhat unexciting reason—biology.

Oxalis plants decide when to open and close in response to a phytochrome chemical. The blue-green substance is similar to chlorophyll and regulates light absorption, which controls the oxalis plant’s growth and survival.

Phytochrome allows oxalis plants to detect light, like human eyes, allowing plants to establish important diurnal cycles. These cycles are similar to circadian rhythms and are responses to the type of light the oxalis plant receives.

A motor organ known as the pulvinus—a joint-like swelling at the leaf base of oxalis plants—is responsible for regulating the nyctinastic response. The pulvinus isn’t present in all plants but works the same as muscles in animals—pushing leaves and effecting closing.

And while it’s unclear exactly why oxalis plants close at night, there are a few working theories out there—all of which are plausible:

  • Protection from the cold. Some scientists believe sleep movements protect the plant from lower night temperatures and reduce the risk of cold-related damage. Others suggest nyctinasty is a way for oxalis plants to save their energy for daytime activities.
  • Keep pollen dry. Evidence suggests that the behavior helps keep pollen dry and increases the probability that an oxalis plant will successfully reproduce. Another leading theory is that nyctinasty is a defense mechanism—protecting themselves from nighttime pests.
  • Moisture retention. Oxalis plants gather water during the day via their leaves, so closing up at night allows this moisture to flow into the plant’s roots.

Regardless of its purpose, nyctinasty is an essential and biologically efficient behavior for oxalis plants. And not only is it necessary to improve a plant’s chances of surviving and growing, but it also makes for a beautiful display.

Does an Oxalis Close in Low Light Conditions?

Now that we’ve gone over how nyctinasty works, and its importance for oxalis plants, let’s explore an important question: do oxalis plants close in low light? After all, low light conditions should affect the plant as much as no light, right?

An oxalis plant closes in low light just as it does at night. Low light conditions like cloudy days and shade can trigger the nyctinastic process, but the leaf movements may not be as dramatic as at night.

The blue-green phytochrome pigment in oxalis plants allows them to detect an extensive range of light intensity, enabling the pulvinus to react appropriately. And since the light response dominates normal circadian rhythms in oxalis plants, your houseplant will respond to slight variations in sunlight intensity.

Therefore, you’ll notice slight leaf curling if your oxalis plant isn’t getting enough sunlight when the sky is cloudy and on foggy days. You’ll also see the plant opening up when you expose it to bright light at night or move it to a position with better sunlight.

Possible Causes for Oxalis Plants Failing to Open

Healthy oxalis plants should open up when it’s morning or after you move them to a position with better lighting. However, you may notice that the closed leaves fail to open in these conditions, making you upset. So, what may be the cause?

Your oxalis plant may not be opening due to watering problems, extreme temperatures, diseases, or the plant is entering its dormancy phase. It might also be a result of low light conditions. So, ensure the plant is exposed to quality sunlight to check if it opens.

Oxalis plants usually become dormant at least once a year as they age or for reproductive reasons. However, the plants may also become dormant or show dormancy-like symptoms when they experience extreme conditions. So, overwatering and underwatering can cause the plant to become inactive or not open.

Temperatures greater than 80 °F (26.7 °C) can also affect the plant and stop the oxalis from opening. But low temperatures, lower than 60 °F (15.6 °C), can do the same.

Still, it’s not uncommon for diseases to affect nyctinasty in oxalis plants, so you must examine them closely and check for color changes and spots. You can check out this article to know more about spots on your shamrocks: Brown Spots On Shamrock Leaves: 3 Causes And Fixes

Tips for Caring for an Oxalis Plant

Regardless of whether your oxalis plant is opening and closing as it usually should, you still need to take care of the plant. Healthy oxalis plants are beautiful and bring color to your home or garden. Fortunately, caring for an oxalis plant is not a hassle since they’re typically low-maintenance plants.

Here are a few tips to correctly care for an oxalis plant:

  • Ensure you put your oxalis in a spot where it can get lots of light. However, limit the plant to early morning and late evening sunlight as the mid-afternoon sun can damage its leaves. You can also opt for a shade or greenhouse.
  • Maintain 30% to 50% humidity around the oxalis plant. You can use a high-quality grow tray to help maintain these levels. And I recommend using a hygrometer to measure the humidity levels accurately.
  • Apply liquid fertilizer no more than twice a month to help grow bushy plants. I recommend using a nutrient-rich liquid fertilizer. Remember to follow the manufacturer’s instructions so you don’t accidentally harm the plants during application.
  • Remember to only water the oxalis plant when necessary. You can use moisture meters if you want to track the water levels in the soil. Remember to only bottom-water the plants with room temperature water.

Combining these practices will ensure you only have beautiful, lush, and healthy oxalis plants in your garden. You can check out this article to know more about growing bushy oxalis plants: How To Make An Oxalis Plant More Bushy


Oxalis plants close at night as a natural response to light changes. This process, known as nyctinasty, happens at night and benefits the plant in several ways. However, nyctinasty can also occur in low light conditions, albeit not as much at night.

Some oxalis plants might have trouble opening due to dormancy, dormancy-related reasons, or because the plant has some disease. Fortunately, adequate care usually helps solve the problem.

Alexander Picot

Alexander Picot is the founder of TheGrowingLeaf.com and its lead content writer. He created the website in 2022 as a resource for horticulture lovers and beginners alike, compiling all the gardening tips he discovered over the years. Alex has a passion for caring for plants, turning backyards into feel-good places, and sharing his knowledge with the rest of the world.

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