Hey plant fans! We’re all familiar with the fact that plants need sunlight to survive.
You’ve heard it since you were a little child everywhere, some of us even did cool little projects in school that proves it. Most of us can even remember the basics of how a plant survives and why it needs sunlight in order to do so.
But is it true? Can plants grow without sunlight?
No, plants can’t grow without sunlight in nature. Although plants can survive for short periods of time without sunlight, they can’t grow without it. The cell of the plant needs light in order to do photosynthesis and get the energy required to grow. However, you could replace sunlight with artificial light.
One other rare exception are parasitic plants, which take their energy from other living plants, thus not requiring light at all.
A little known fact is that if the plant is green it needs sunlight or replacement artificial light in order to survive and grow.
Most often we associate the light that plants need to survive with the Sun but this is not necessarily true. It isn’t that simple either, so let’s take a closer look at this subject:
Photosynthesis. If it’s one word that unites all non-plant people with the rest of us, it’s photosynthesis.
We’ve all heard it, learned about it, studied about it, but what’s the big deal?
Well, it’s the magical process through which your plants eat.
The reason why it’s so magical is that plants are autotrophs, which is a fancy word for how they prepare their own food from scratch before eating it.
What is photosynthesis and why does it need sunlight?
Plants take carbon dioxide from the air, water from the roots and use light as the fuel to create glucose, sugar if you will and also produce as waste that thing we all love called oxygen.
That’s one of the big reasons why plants are not only important, but necessary to life itself.
So we all breathe plant poop.
But it gets even more interesting. Have you ever heard that sunlight is actually composed of different colors?
Well, plants contain a molecule called chlorophyll.
Chlorophyll is responsible for absorbing light. More precisely, chlorophyll absorbs red and blue light, and reflects green light back.
The magical rule here is that if the plant is green, it needs light in order to feed itself and survive.
This entire process we talked about happens in the leaves which is also the part of the plant that is always green.
Flowers don’t usually have the color green, which means they don’t have chlorophyll and so they serve another purpose.
I am sure that you might have noticed how leaves are flat but wide. They usually have a plate-like shape and the reason for that is the more surface area they have the more amount of sunlight they can absorb.
They also have small veins that are used for transporting water and minerals.
Besides the whole process being complete and independent of anything else, the cool thing about this whole process is that the waste product from photosynthesis is oxygen.
So, in one way the thing that we breathe and it’s essential for you and me being here is plant poop.
Plants also do cellular respiration, a process in which they take in oxygen. This is what created the myth that plants can kill you at night.
And now you know the reason why I’m obsessed with plants, how can you not?
How Long Can A Plant Survive Without Sunlight?
We will ignore artificial light for this one and only talk about natural light sources, more specifically sunlight.
But first, let’s talk about it about what sunlight really means.
When someone asks me how much sunlight a plant needs, what they usually mean is how much direct sunlight they actually need.
The mind instantly goes to a ray of sunlight shining through the window.
If a plant is not sitting in direct sunlight it doesn’t mean it’s not getting any sunlight.
Let’s do this thought experiment, you move your plant from the window and put it in a dark corner of your room.
You will still see the plant which means photons are bouncing around the room hitting your eye, but they are also hitting the plant, that’s why you can see it.
The plant still makes use of that, it’s not as rich as direct sunlight is, but it’s still a light source and plants are really good at taking advantage of any light sources.
How good a plant is at taking advantage of light sources really depends on the species of the plant and the need they have for it, as we know there are hundreds of thousands of species of plants coming from all corners of the world.
There are plants that grow in the desert or in areas that get 12 hours of direct sunlight and as such they are really dependent on getting as much direct sunlight as possible.
Others have adapted very well to live in really low-light conditions.
If you think of tall and thick rainforests, there is barely any light reaching the ground and such plants have adapted to live and thrive in high humidity and low light.
Because some plants naturally need more light and others less, your houseplant can live for the rest of its life pretty happily in a dark corner or in a bathroom with no windows, or it can die pretty quickly in such conditions.
In order to understand how much sunlight a plant needs we use illuminance or lux, which is a unit used to measure the light intensity hitting a surface.
To really understand lux in the real world here are a few examples that anyone can understand:
|Clear night sky||0.2 - 0.5|
|Standard living room lights||100|
|Sunrise or sunset||400|
|Office lighting||300 - 500|
|Overcast day / Studio lighting||1,000|
|Full daylight, not direct Sun||10,000 - 25,000|
|Direct sunlight||32,000 - 100,000|
As you can see there can be a massive difference between the amount of sunlight your house plant gets In the living room and if it were to be outside in direct sunlight.
Having a way to accurately measure the amount of light your plants are getting will help you go a long way in growing healthier plants. In order to do that you will need a Lux metre.
Lux meters can be expensive and not that accurate, so be careful what you purchase and do proper research.
With the information above, we can split plants into three main categories based on how much sunlight they need:
1. Low-light plants (500 – 2.500 lux/day)
These are usually plants that have adapted to low light conditions and can survive with as low as 50 lux/day, but they need a bit more to thrive.
Commonly, they tend to be tropical plants that enjoy humid environments, although not necessarily.
A Snake Plant is a good example of a low light low humidity plant. In fact, many of these plants will get leaf burns from direct sunlight. A good way to spot them is by their abundant green leaves, and the fact that they don’t flower as much or as spectacularly as other plants.
They follow the green rule, the more green leaves they have the more they can get the advantage of low light conditions.
A few examples in no particular order:
- Chinese evergreen
- Spider plant
- Snake plant
2. Medium-light plants (2.500 – 20.000 lux/day)
Medium-light plants can survive as low as 250, but they need more than that to thrive and flower.
Medium-light plants are actually great recommendations for beginners. They are usually in line with the classic stereotype of plants. You give them some water and some sun and just watch them grow. They also flower pretty nicely and give you a splash of color, keeping beginners a bit more engaged.
As a rule of thumb, these plants like it medium on everything.
They also tend to like moderate temperatures and relatively moist soil. Because they don’t like any extremes, you can place these plants 5 feet or more away from a sunny window.
A few examples:
- African violet
- Dumb cane
- Kentia palm
3. Bright light plants (20.000 – 100.000 lux/day)
These plants need at least 2000 lux/day to survive and much more to thrive and flower.
More often than not, these are plants that evolved in the desert or in conditions where they get constant direct sunlight. As a consequence they generally prefer drier conditions, so they are used with their soil being drier.
They should be placed at the window or in any place that receives a fair amount of direct sunlight at least five hours a day.
A few examples:
- A lot of cactus species
- Other succulents
- Jade plant
- Areca palm
So can plants grow without sunlight?
Technically not, although there is a way around it.
Then, how long can any plant type survive without sunlight? take a look at the table below.
|Plant type||Necessary lux/day||Survival period with no sunlight ( ~0 lux/day)|
|Low light plants||500 - 2,500||14 - 20 days|
|Medium light plants||2,500 - 20,000||10 - 14 days|
|Bright light plants||20,000 - 100,000||4 - 10 days, except hibernating cacti|
Can Plants Grow Without Sunlight? (Science Experiment)
How can we test this? I suggest you make the following experiment that some of you might be familiar with from school.
It is also called the closet experiment:
- Take a notebook and pen if you want to document the stages and when they happen.
- Take one potted houseplant. Keep it classic, a medium-light green leaves houseplant.
- Put the house plant in a dark closet with enough space. You can keep watering it as this is a no sunlight experiment. It will give even faster results if you give it water but it has no fuel to do something with the water.
I don’t want you to kill your favourite houseplant, so let me walk you through the next stages of the experiment and what will happen:
Phase 1 – Pale leaves
They can’t produce enough chlorophyll anymore, which is also what gives leaves their green pigment. As a consequence, they lose the green color and the ability to use sunlight as energy at the same time. The leaves will take a yellow color and fall off.
Phase 2 – Leggy plant
You might have heard the term leggy plant. This is an amazing phenomenon where if the plant is not getting enough sunlight it grows trying to reach more sunlight. As a result, it becomes overly long and topples over.
Phase 3 – Death
I think the name of this phase tells you all you need to know.
There are some plants in the plant world that we did not mention here, and they are the only plants that can live without sunlight or artificial light, parasitic plants.
Parasitic plants, black sheep of the family
There are some plants that can grow without sunlight, they don’t even need artificial light, and they are really creepy.
Parasitic plants rely on stealing energy from a host in order to survive, like a plant vampire.
Some plants can even do both photosynthesis and stealing of energy from the host. They are hybrids, like the Mistletoe.
Because they don’t rely on having leaves, they don’t have the color green, which results in alien and odd-looking plants.
Some of them are spectacular, they can have ghostly shades of color and look like small flowers growing from the ground, like this beautiful Indian pipe.
If you are interested in parasitic plants and want a more in-depth guide on them, click here to check out this introduction into their world.
Can You Grow Plants Using Artificial Light?
The short answer is yes, plants can survive and even thrive on artificial light, notice how when I explain photosynthesis I didn’t specifically refer to sunlight.
The only reason plants grow without sunlight is that we used this big brain of ours and discovered artificial light.
That’s how we learn from the textbooks because that’s how plants evolved, but the molecule responsible for the process doesn’t care about where the light comes from as long as it is yummy.
What yummy means for your houseplant is a light source that has the wavelengths it needs in order to use it as fuel. Remember how Einstein, that small dude with a big brain said that light can come in waves too? Well, turns out that that’s important plant information.
The tricky part here is that the sun provides the full light spectrum and plants really need that during their different growth stages.
That’s where the term growth light comes from, and they aim to complete or provide the full light spectrum your plants need to thrive.
When it comes to the best growth lights, we can separate them in 3 main categories:
1. HPS lights or High-pressure sodium
These are the most powerful but also the generally most expensive. If you just need a bit of light to grow a houseplant, I don’t recommend these, they are a bit of an overkill. However if you need a powerful, reliable growing lights they are very good.
2. Fluorescent lights
As you can see they are cheaper and more practical, but not that safe and they tend not to work so well for beginners unless you know what you are buying. However, If you need light for a few houseplants, these are the best and I would highly recommend you this one:
3. LED lights
They are somewhere in the middle as far as price goes. The price can also widely vary. A few years ago LED Grow lights where a luxury but now, it’s the safe choice.
They are very safe and adaptable, but they tend to be less practical if you need a lot of power. That being said you can usually find what you need. I linked a very powerful example below, but you can find them much cheaper if you don’t need all that power:
They are not the same quality, but all artificial light types can help you complement or replace natural light.
Choosing between them can be tricky and save you a lot of money.
All this talk about light could make us forget something really important, darkness or lack of light is just as important for plants.
Another thing to always remember is that plants love darkness too. Similar to us they need a break where they just enjoy a good sleep, so giving your houseplant a break from feeding is really important.
Plants are pretty cool and if we take care of them they will take care of us, even though that technically means us breathing more plant poop.