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Are you wondering why your Calathea plant leaves stand up at night? You're not alone. Many people wonder if this is normal behavior or if the plant needs care. Calathea leaves move due to a phenomenon called nyctinasty, which occurs when the plant reacts to changes in light levels to enable better photosynthesis during daylight. This is a common occurrence in Calathea and may indicate a healthy plant. In fact, your Calathea plants may be under stress if their leaves do not move throughout the day. In this article, you will learn more about: How does Calathea manage to move its leavesWhy do Calathea leaves close at nightDo all Calathea varieties move its leaves throughout the dayPossible reasons why Calathea leaves not closing at night Let's get started Nyctinasty in Calathea: How Is It Possible? Nyctinasty is a common response in plants that grow in the dark, such as those found in the rainforest. By standing up at night and opening during the day, they can maximize their exposure to light and photosynthesis. If you're curious to see nyctinasty in action, just take a look at your Calathea leaves during the day and night. You'll be able to see them slowly opening and closing as they adjust to the light levels around them. Illustration by isaacperper.com In Calathea, the nyctinasty movement is controlled by the pulvinus, which is a small region of cells that act as an elastic hinge between the leaf blade and petiole. The pulvinus cells elongate when light levels decrease and create tension between the leaf blade and the petiole. As a result, the leaves point upward almost like the plant is folding up its “hands” for prayers. On the other hand, when light levels increase, these cells relax and the leaves return to their original shape. It allows them to absorb more light for photosynthesis. While it may seem like the plant is actually getting larger during daylight hours, these movements result from cellular changes in the pulvinus and not from any growth in the plant itself. Why Do Calathea Leaves Move? While the reason for nyctinasty is still being studied, it's believed to be related to changes in hormone levels or the plant's circadian rhythm. Plants need consistent light and dark periods in order to grow and function properly. There are other theories on why Calathea leaves move, though: For one, some believe it's a way for Calatheas to regulate temperature and water loss. By folding its leaves, the plant has less exposed surface area, and is therefore less likely to lose heat during the cool hours of the night. Another possible theory is that the plant closes its leaves to protect against fungal infections. Rather than pooling on the surface of the leaves, water would drip from the leaves down to the roots when they stand up. Last but not least, Calathea leaf movement could serve as a means for the plant to defend itself against pest infestation. Standing leaves could make it more difficult for bugs to hide from predators. Whatever the reason, I'm sure you'll agree that Calathea leaf movement is a very cool process. Do All Calatheas Close at Night? All Calatheas can close their leaves at night, no matter the species. It's an innate response that has evolved to help plants conserve energy during periods when they're less active and exposed to lower light levels like those found in the evening or on cloudy days. Healthy Calatheas will close their leaves at night and open them again in the morning. However, if a plant is unhealthy or stressed, it may not be able to respond appropriately to light stimuli, and its leaves may remain open all the time. A Calathea that doesn’t close at night indicates a severe problem. Your plant may be under stress, and it’ll require intervention in order to function correctly once again. Why Is My Calathea Not Closing at Night? If your Calathea isn’t closing at night, there are several possibilities to consider. Your Calathea is not closing at night, likely because it's exposed to too much light. But overwatering or underwatering can also cause the problem. Other reasons include pest infestation, low humidity, temperature stress, physical damage, and aging. I’ll discuss these reasons in more detail down below. Exposed to Too Much Light (Most Common) Too much light exposure can disrupt the plant's natural photoperiod and cause it to stop closing its leaves at night. Move your plant to a shadier location to ensure it's not suffering from sunburn or heat stress. If you can’t locate your plant to a shadier location, consider using a sheer curtain to block out some of the sunlight. You may also add grow lights to help maintain its natural photoperiod. Overwatering Issue If your Calathea isn’t closing at night, the most likely culprit is improper watering practices. Overwatering your Calathea can cause root rot and damage to the plant's xylem tissue that transports water up from the roots into the leaves for photosynthesis. In addition, if your plant is getting too much water, the soil can also become too wet, and the leaves won’t be able to close properly. Make sure you’re watering your plant correctly and only when the top 2 or 3 inches (5.08 or 7.62 cm) of soil feel dry to the touch. Allow the pot to drain completely after watering, and never let the plant sit in waterlogged soil. Underwatering Issue If your Calathea isn’t closing at night, it may be due to underwatering. When a plant doesn’t receive enough water, its leaves will droop, curl and wilt as a way of conserving water. It’s an adaptive response known as the "wilting reaction." Be sure you’re watering your plant correctly and give it a good soaking once a week to keep the soil moist but not wet. You may need to water your plant less frequently during the winter since the cooler temperatures will slow down its growth. Pest Infestation Insects and other pests can also interfere with the plant's ability to close its leaves at night. For example, an infestation of aphids, mealybugs, or most commonly, spider mites can cause deformities and other problems that prevent the plant from closing its leaves. If you suspect an infestation is preventing your Calathea from closing at night, inspect your plant closely and treat any problems accordingly. Use an insectidal soap spray to kill any insects on contact and their eggs before they hatch to prevent future infestations. Low Humidity Calatheas require adequate humidity to close their leaves at night. If your plant is in a dry environment, it may not be able to absorb enough moisture through its stomata to trigger the closing mechanism. Keep an eye on humidity levels and use a plant humidifier if necessary during periods of low humidity or A/C use. You can also use a moisture meter to test the humidity levels in your home and adjust your watering practices as needed. Temperature Stress Temperature stress is another common problem that prevents a Calathea from closing its leaves at night. If your plant is too warm, it may not be able to close the pores on its underside in order to prevent water loss through evaporation. The appropriate temperature range for Calathea plants is 65–90°F (15.56–32.22°C). If the plant gets too hot or cold, it won't be able to close its leaves at night even if other environmental conditions are optimal. When moving your plant around, keep this in mind and make sure you look after it during extreme heatwaves or cold snaps that may affect your region. To maintain an appropriate temperature, you should consider using a fan to circulate air and keep your plant away from heat sources such as appliances and direct sunlight. Damage to the Part That Makes Movement Possible Physical damage to the plant from pests or mishandling can also prevent your plant from closing its leaves at night. The mechanism that causes the movement is in the pulvinus — it controls how much tension to apply when opening or closing. Suppose you damage this part of the plant by crushing or breaking it. It won’t be able to close properly or remain open during the day. If you suspect damage has occurred, inspect your plant closely for any abnormalities and treat it as necessary. Leaf Aging You can spot aging leaves by their yellowing color and wavy edges. As the leaves age, they become less elastic and begin to droop. When a Calathea plant ages, it'll lose its ability to close at night. It's normal and expected as the plant reaches the end of its life cycle. Aging leaves may stop responding to light stimuli and will eventually die off and fall from the plant. You can remove these leaves by pruning them with sharp scissors to maintain the healthy appearance of your Calathea. Removing leaves that are yellowing or browning will allow the plant more energy for new growth. It helps the plant absorb more nutrients and stay healthy. Other Plants That Move at Night In addition to Calathea, there are many other nyctinastic plants. Many types of legumes are also nyctinastic. For example, Papilionid beans and other types of climbing vines will fold their leaves as the light fades so they can absorb more carbon dioxide during this time. A few flowers are also nyctinastic, such as: Oxalis triangularis (False Shamrock)DaisyCalifornia poppyLotusRose-of-SharonMagnoliaMorning glory