Cacti are popular houseplants due to their exotic look and fascinating features whilst being low-maintenance at the same time. Cacti thrive in hot, dry and arid desert conditions and are known for their adaptations such as their spiky spines.
Sunlight is essential for all plants to survive, including cacti. In this article, we are going to answer the question – how much light do cacti need. We will also discuss what makes cacti unique and the importance of direct sunlight for cacti.
Let’s dive in.
How much light do cacti need?
Cacti need to between 10-14 hours of light per day depending on the season.
It’s essential that you don’t expose your cactus plant to more than 14 hours of light per day. Too much direct sunlight can cause sunburn damage leading to permanent damage or death.
Alternatively, If your cactus doesn’t receive enough sunlight it can lead to etiolation, severely damage or even kill your cactus.
What makes Cacti Unique?
Cacti don’t live exclusively in hot, sandy deserts. Some species of cacti prefer mountain areas, and some even thrive in tropical forests! They don’t have true leaves. Instead, their leaves have evolved into spines, which grow from small bumps known as areoles. Most cacti have spines, but some are covered in hairs instead, or they are completely spineless.
Cacti stems are juicy, succulent (storing water), full of chlorophyll, and photosynthetic. Cacti come in all shapes: some are round, some grow like flat pads, and there are even those that look like stars! Some cacti prefer to grow as solitary plants, whilst others grow in clumps.
Their sizes can also vary: some cacti have a radius of only a few centimetres, whilst the others reach a staggering height of 20+ meters. Cacti have beautiful flowers too, and some species flower at least once a year, whilst others flower rarely, sometimes as little as once in every 20-30 years.
There are cactus species that produce edible and delicious fruit, whilst others are known to have some psychoactive characteristics.
Why do plants need sunlight?
Plants need sunlight to function properly.
Different plants have different light requirements, but they all have one thing in common – they all need at least a small amount of light.
Photosynthesis, a process in which a plant produces the energy needed for growth and reproduction, is highly dependent on sunlight. Plants that don’t receive enough sunlight become weak and eventually die.
During photosynthesis, plants take CO₂ from the air and release oxygen that we need to breathe.
Because of photosynthesis, sufficient levels of oxygen in the air are maintained, which is beneficial for all other living creatures on eath.
But, the importance of sunlight for plants doesn’t end there.
Without sunlight, plants wouldn’t know in which direction to grow. When a seed is planted, it needs light and gravity to sprout successfully. Roots grow in the direction of gravity, while stems with young leaves grow in the direction of sunlight.
How much sunlight do cacti need?
Since cacti usually grow in deserts, they need around 10 – 14 hours per day. Cacti prefer the pleasant morning sun over scorching afternoon sunlight. This is especially true for younger, more fragile cacti.
Mature cactus plants are more resistant and can take more direct sunlight.
How much sunlight a cactus needs also depends on the time of the year. Cacti usually go through periods of growth followed by periods of dormancy.
For most cacti, the growth period is during spring and summer. When they are actively growing, cacti need more sunlight. But in late autumn and winter, cacti enter their dormant phase. They stop growing and instead focus their energy on surviving colder temperatures while simultaneously preparing and storing energy for the next growing season.
During this phase, cacti need less sunlight and almost no water, in order to overwinter successfully. When winter ends, cacti are still sensitive and in that period they prefer sunlight intensity to be gradually increased.
Exposure to strong sun rays right after the winter can be too much for cacti. Also, sunlight requirements can vary depending on the species.
As we have already mentioned, some cacti live in forests instead of deserts. They are used to living next to the much higher trees and other plants that obstruct direct sunlight, so they evolved to thrive in bright, but indirect sunlight. For these cacti species, constant direct sunlight could be fatal.
What happens if a cactus gets no sunlight?
If a cactus gets no sunlight it will soon become etiolated.
Etiolation is a process of unhealthy growth, during which a plant rapidly grows in height in order to reach more light. Etiolated plants are long, thin, and usually pale green or yellow. Etiolated cacti become more prone to various diseases, like fungal and bacterial infections, pest attacks, rotting, and even breaking off the etiolated parts.
Most elongated cacti grow in one direction which can cause them to become significantly tilted, lose their balance, and fall over. They also lose their usually full shape and become elongated, which sadly ruins their beauty. Even after the cactus starts receiving more light, the etiolated part remains thin and weak forever.
Do cacti need shade in the desert?
Although cacti love sunlight and need lots of it, sometimes sunlight becomes too strong for them.
That’s another use of their spines, they partially protect the plant from excessive UV rays from the harsh, direct, desert sun. Sun can be especially unforgiving in high mountain areas where UV rays are much stronger because of lower air density.
That’s why a lot of cacti that grow there have fine, white hairs to protect them.
That’s not always enough. Some desert cacti grow inside cracks in the rocks, or almost completely underground, with just a tip above the ground level. When cactus grows in clumps, younger offshoots grow from or beside the more mature plants. These younger and more sun-sensitive offshoots are often protected by the shade of mature ones.
Cacti Sun Damage
Sometimes strong sunlight is simply unavoidable for a cactus, and when exposed to strong sunlight, the cactus can become sun-stressed.
Sunstressing is manifested through a change of colour in the cactus, during which a green colour transforms into various shades of yellow, red, and even purple.
Sunstressing isn’t necessarily bad for a plant though, it’s a similar process to our skin becoming tanned. The plant produces different pigments to protect itself from strong sunlight, just like our skin produces melanin. When sunlight becomes milder and more tolerable again, the cactus reverts to its original colour. If however, strong sunlight persists or becomes stronger, cacti are at risk of getting sunburned. Sunburns manifest as brown splotches on the cactus.
Unfortunately, sunburn doesn’t go away even after cacti start receiving more moderate amounts of sunlight. The sunburned area will heal, and the cactus will survive but it will remain scarred.
In more extreme cases, if the sunburn is too serious and all over the cactus plant, the cactus might die.
Summary: How much light do cacti need?
Cacti need between 10 – 14 hours of sunlight per day depending on the season.
Sunlight is crucial for photosynthesis and therefore, for oxygen production and survival of all plant and animal species on planet Earth.
Cactus, as a plant species that mostly grows in deserts, needs massive amounts of sunlight, otherwise, it can face various issues with its growth and have lowered pest/disease resistance. But, sometimes the sunlight can be too strong even for cacti, and they need some protection in order to avoid sunburn. In the end, temperance is the best, even for plants like cacti!
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