In the desert, cacti get a lot of light, and they love it. But without light, will they still thrive? Of course many will tell you that “Yes they need a light”. But do they really? How long cacti can stay without light? Here I spend a month doing intense experiments with photos and in-depth analysis to answer just this question for you! Brace yourself, it will amaze you!
Cacti cannot live indefinitely without light. Nevertheless, the experiment shows that cacti can easily survive a few weeks in total darkness. The lack of light will cause 1) discoloration and 2) etiolation in as little as 21 days. This change is significantly based on the light requirement of the cactus.
The presence of light plays an essential role in plant growth. Check out the experiment I conducted about the effect of light on cactus growth.
Table of Contents
- 1 The Experiment Set-Up
- 2 Without Light: Cacti Experiment Results [Time Lapse Photos]
- 3 How Much Light Does A Cactus Need?
- 4 How Does Light Differ Depending On The Cactus Type?
- 5 Can Cactus Survive Low Light?
- 6 Cacti That Demands Minimal Light
- 7 Cacti That Requires Lots of Light
- 8 Does a Christmas Cactus Need Light?
- 9 Easter Cactus Light Requirement
- 10 Zebra Plant Light Requirement
- 11 Takeaways
- 12 Sources
To start the experiment, I gathered four cacti of different of two different species from my collection:
- Two Echinopsis Subdenudata (Easter Lily Cactus) – Bright, direct/partial sunlight requirement
- Two Gymnocalycium Mihanovichi (Chin Cactus) – Bright, partial sun/partial shade light requirement
One cactus of the pair is the “reference” while the other is the “test” cactus. I chose the cactus so the test and the reference one looked identical before the experiment. This is because we need to understand how badly the lack of light affects them over time.
The “test” cactus were put inside a covered box with small side holes for air to get in and circulate for a month In this condition the cactus under experiment did not take any light whatsoever.
In the photo above you can see how the reference cactus is beside the box for comparison.
The test and control samples received the same amount of water with sunlight as the only independent variable.
I took photos of each specimen every week to document any signs of change. The setup remains on the same spot inside the greenhouse until the end of the experiment.
The test cacti (without light) exhibits 1) signs of discoloration and 2) etiolation just after 21 days. However such effects are way more evident in high-light cactus. Cactus that require low light can survive way longer periods and show very little effect even after a month of no light exposure.
Discoloration: The originally green apical meristem of the Echinopsis becomes slightly yellow on the center. The signs of light starvation became more evident in the preceding weeks as the color fades and the form is distorted from the tip. The paleness is due to chlorophyll loss as it is deprived of sunlight.
Etiolation: From there, it is clear that the cactus needs more light as it stretches its tip to look for a light source resulting in elongated growth. This causes the cactus to lose its round shape and lose its natural shape. To note that this is a well-known effect that happens to many plants, herbs included, in case of lack of light. The stretching and color loss behavior is called etiolation. If the cactus stay in the box for another month or so, chances are it will become more elongated and lose more chlorophyll that will lead to a weak and sickly plant.
However, for low-light cacti like the Gymnocalycium mihanovichii used in the experiments, this might not be the case.
The results of the experiment below show that this species can survive darkness for longer. The only evident change I see is the growth of its spines. It grows more extended and more erect. But the color and form of the cactus remain unchanged.
How can you tell that your cactus isn’t getting light?
Generally, cacti are slow-growers. Signs that a cactus is starving for light includes discoloration and deformation on the center tip. Color varies from dark to light, and the once full rounded shape grows into a narrow point.
Cactus requires light energy to carry out photosynthesis for natural growth and nourishment. Even a cactus with the lowest light requirement still needs light to survive. Sunlight is the primary source of energy required by most plants to produce their food. Several days or months without light will cause the cacti to grow weak and unhealthy.
Echinopsis Subdenudata test sample (top row in the photo above) was placed inside the box for one month. Changes in the color and form of the specimen are apparent after 14days, indicating that the cactus needs light.
Can the etiolated cactus recover?
Etiolated cactus will not revert to its original form but it will continue to survive if given adequate light. When putting the cactus back to light, make sure to do it gradually to avoid sunlight shock.
Typical cacti need 4-10 hours of light per day to maintain their natural growth. However, the amount of light required depends on the cactus variety. It is essential to observe the cactus and assess its light preference.
Plants don’t generate chlorophyll (the green pigment in plants) when they can’t get enough light, and their color changes from dark green to yellow to white. To compensate for the low-intensity light, plants increase the number of hours they are exposed. Increasing the duration of light exposure enables the plant to produce sufficient energy for its processes.
If you live in areas where light is scarce, artificial light is an excellent alternative source of light waves required by the plant. This artificial grow light below is recommended by its effectiveness to produce the right amount of light.
Light requirements greatly vary for each cacti species. Some cacti prefer low light, most require more sunlight, and others just prefer part shade.
The majority of cactus species do not require direct sunlight to grow. Cacti thrive in areas with good light but not necessarily direct exposure. Other cacti are grown indoors with low to moderate indirect or filtered light because they cannot tolerate intense sun rays and get sunburn quickly. They are cacti with soft, waxy, thin stems and fewer spines that cannot withstand prolonged sun exposure.
While others are sensitive to too much light, some species thrive well under direct full sunlight. They enjoy the heat of the sun without being scorched. Their spikey and hairy stems protect their body from intense sun rays.
Apart from sun-loving and shade-loving species, there are also neutral cacti. They are species that do well both under direct sun or part shade.
With over a thousand cacti species, some grow best under low light as bright sunlight can harm them. Cacti species with minimal light requirements will precisely survive under low light.
Low light means the plant cannot receive direct sunlight because it is away from the light source. Cacti species such as schlumbergera and Rhipsalis do well under light shade. They are spineless with leaf-like stems making them sensitive to bright and direct sunlight, especially in summer.
The stems tend to wither and burn with prolonged bright light exposure. They are often grown indoors or under large trees where the sun cannot reach them.
Some species prefer bright light but can tolerate short periods of shade.
However, for most cacti that require long hours of intense light even a short period without light can be detrimental. They quickly tend to etiolate when shaded.
Just like in the case of my experiment, the Echinopsis test sample shows evidence of etiolation after a month inside the box. It is shade sensitive because it reacts quickly in darkness. In contrast, the Gymnocalycium test sample shows no apparent sign of etiolation. It means it can tolerate shade for an indefinite time.
One of the misconceptions about cacti is that they all love the desert sun. But the truth is, cacti have different light requirements.
Epiphytic cacti in rainforests are often found growing near the roots or among branches of large trees. These cacti are not parasitizing but getting protection from intense sunlight. They are species that need shade from the brightest light of the day to thrive well. These species will make an excellent indoor plant addition.
Epiphytic cacti examples are :
- Schlumbergera Species – these cacti are usually grown hanging as houseplants to keep them away from sunlight. Some examples of schlumbergera species are Schlumbergera truncata (Thanksgiving Cactus), Schlumbergera x buckleyii (Christmas Cactus), Schlumbergera gaertneri (Easter Cactus).
These three are often confused with each other, but their stems and flowers distinguish the key characteristics.
- Rhipsalis Species are native to rainforests and belong to the epiphytic cacti family with little to no thorns and very thin drooping stems. There are over 35 species of Rhipsalis with varying forms and sizes. Some known Rhipsalis species are Rhipsalis baccifera, Rhipsalis flagilleformis, and Rhipsalis Pilocarpa.
Few cacti species can tolerate shade for indefinite periods without being etiolated. They are not epiphytic, but they have dark green stems that absorb and store enough energy for several days. This characteristic enables them to survive a few days or months under the shade.
Gymnocalycium species such Gymnocalycium mihanovichii, Gymnocalycium anisitsii, and Gymnocalycium Baldianum are examples of shade-tolerant cacti.
Cacti with prominent spines and thick wools will need more hours of direct light.
The cactus spines and thick hair or wools enable the plant to withstand the sun’s scorching heat. Their primary function is to provide shade for the cactus’s green, sensitive epidermis beneath. The shade given by the spines reduces the temperature of the cactus’ body, limiting the quantity of water lost.
Cacti such as Echinocactus grusonii’ Golden Barrel’, Saguaro cactus, Cephalocereus senilis, Melocactus, Opuntia, and Ferocactus are examples of cactus that thrives under direct sunlight exposure. Even though they appear to grow well in partial sunlight, they seldom reach their full potential to maintain their shape and color, and they rarely bloom.
Schlumbergera x buckleyi or Christmas Cactus are epiphytes and thrive under a shade, but they still need light. Without light, Christmas Cactus cannot perform photosynthesis.
Unlike most epiphytes, Christmas Cactus does not parasitize. They become epiphytes in the sense that they can attach their body to large trees to get some shade. But they don’t get their food from the tree they’re attached to. They manufacture their own with the help of light that they absorb from the sun. A Christmas cactus often need extra light to stimulate budding.
Schlumbergera gaertneri or Easter Cactus prefers bright, indirect sun but also thrives under minimal light. That’s the unique characteristic of this species.
Like other schlumbergera species, Easter Cactus grows best indoors where light is sufficient but away from direct sun rays. You can place the plant in an east-facing window where the sun is not on its hottest. The filtered morning sun is favorable, so make sure that the plant gets shaded in the afternoon.
The Zebra plant belongs to the Haworthia species. They grow best under 4-6 hours of partial sun but can tolerate partial shade.
Haworthia fasciata ‘Zebra’ belongs to an aloe family succulent plant that is easy to cultivate. It has erect and pointy leaves with small white lines that resemble zebra stripes, thus the name. The plant prefers light shade but can tolerate short 2 hours of full sun during the day.
When exposed to the light, the leaf takes on a beautiful crimson color and stays compact. Zebra plants are a great accent to any north-facing windowsill and readily accessible in many cactus dealers’ nurseries. They require little maintenance, making them a fantastic houseplant and an excellent plant for novice enthusiasts.
- Cacti cannot survive without light since it is the primary source of energy they need to manufacture their food.
- Other species can survive low light for long periods, while others cannot tolerate darkness and will etiolate quickly. However, some can tolerate insufficient light for few months.
- Generally speaking, cacti species need a minimum of 4hours and not more than 10 hours of sunlight daily. Cacti require periods of darkness needed for CAM photosynthesis.
- Epiphytic cacti can tolerate low light levels but hate intense direct sunlight.
- “Etiolation,” Biology Department, University of Massachusetts
- “Lighting for indoor plants and starting seeds,” University of Minnesota Extension
- “Thanksgiving and Christmas Cactus,” Clemson Education
- “Schlumbergera gaertneri (Easter Cactus),” North Carolina State University
- “A remarkable new Rhipsalis (Cactaceae) from eastern Brazil” Academia Education
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