Can Plants Photosynthesize Through Glass


Peace Lily Houseplant in bathroom window Sill with Low Light Dappled Light

Every plant must photosynthesize, but you wonder if it’s possible for them to do it through glass. For example, could your houseplant make use of sunlight if that light passes through a frosted bathroom window first? I think you might be surprised by the answer.

Can plants photosynthesize through glass? Yes, your indoor plants can photosynthesize even if their light sources passes through a glass windowpane. In fact, your plants aren’t particularly discerning about what light source they use, provided the light is sufficient for photosynthesis.

How much light does a houseplant need to photosynthesize? Why do plants even undergo this process, anyway? Keep reading, I’ll answer those questions and a few more before the end of this article.

Photosynthesis Through Glass: Is It Possible?

A Deep Dive into Photosynthesis

Before I elaborate more on why houseplants can photosynthesize through a window or other glass, I wanted to discuss the process of photosynthesis more first.

Yes, this is a popular topic that’s come up on this blog before (several times, actually), and it’s also probably a topic you already have at least a passing knowledge of.

Because, every plant, indoor or outdoor, must photosynthesize for survival its worth covering in more detail.

At its most basic, photosynthesis is the conversion of carbon dioxide into oxygen, which we humans then breathe in.

Let’s now go a little deeper into the process of photosynthesis than we have before. This way, no matter which situation you put your houseplant in, you’ll have a good idea of whether it can provide for itself or will need extra help.

When a houseplant photosynthesizes, it creates its own chemical energy. This chemical energy can trigger chemical reactions, but most plants use it as an energy source for basic houseplant activities.

Sugars or other carbohydrate molecules hold onto the chemical energy. These sugars, a synthesized form of water and carbon dioxide mixed, are the namesake of photosynthesis.

Where does the chemical energy come from? It’s not like your indoor plant can just make something from nothing, right? Correct. The plant uses what’s known as radiant energy or light energy to transfer it into chemical energy.

Can Plants Photosynthesize Through Glass?

Light energy can come from a variety of sources. For outdoor plants, the light is exclusively from the sun. With indoor plants, they have more options (which we’ll discuss later). When the plant is exposed to this light, its reaction centers will absorb it. The reaction centers are plant proteins contained within the chloroplasts, which are commonly found in the houseplant’s leaves. These proteins have chlorophylls that are pigmented green.

Upon receiving the light energy, the houseplant immediately uses some of it to reduce the quantity of electrons within the water inside the plant. This leads to the creation of oxygen gas. There’s also hydrogen, which can make compounds known as adenosine triphosphate and nicotinamide adenine dinucleotide phosphate. Yes, that’s a mouthful, but what you need to know is that ATP and NADP are two forms of chemical energy.

Yes, that’s a mouthful, but what you need to know is that ATP and NADP are two forms of chemical energy.

That’s the process of photosynthesis in a nutshell. You have no questions now about whether the process can occur if your houseplant sits near a sunny window. What about if that window is closed?

Absolutely, photosynthesis can still happen! Think about greenhouses. These have countless windows yet all the plants and flowers inside survive. In fact, they grow and thrive.

Windows can be beneficial for your houseplants, in that many can prevent UV rays from getting to your plant. These could lead to your houseplant aging prematurely, as UV rays are a form of radiation.

What Are the Benefits of Photosynthesis?

If photosynthesis wasn’t good for your houseplants, then they wouldn’t bother doing it. Still, you’re curious what the advantages of photosynthesizing are. We’re glad you asked. Not only is photosynthesis a useful process for plants to undergo, but it’s beneficial for us people as well.

Here are some perks our planet enjoys everyday thanks to plant photosynthesis.

Provides Energy to the Houseplant

Your indoor plant probably doesn’t look like it’s doing much to you. It doesn’t move or show many signs of life, but behind the scenes, a lot is going on. When you water your houseplant or nourish its soil with fertilizer, it needs energy to absorb the water and nutrients. Your plant will also rely on this energy to bloom and grow. Photosynthesis makes this all possible. Without it, your poor houseplant would be small and withered. It also probably wouldn’t survive.

Keeps the Planet’s Carbon Cycle Alive

Our earth has what’s referred to as a carbon cycle. This is a cycle of biogeochemical nature in which the earth’s atmosphere, hydrosphere, geosphere, pedosphere, and biosphere pass along carbon. Photosynthesis can produce this carbon as carbon dioxide. During respiration, the carbon comes back to the earth and the process begins all over again.

Every living thing needs carbon. Through the carbon cycle, it’s possible for carbon to transfer to the oceans and the atmosphere and then back again, ensuring healthy life for all.

Gives Us Oxygen

The next time you take a deep breath, thank your houseplant. Our world is rife with plentiful oxygen, and plants are mostly responsible for that. Through photosynthesis, plants produce most of the oxygen in our atmosphere.

Will a Plant Photosynthesize in the Dark? What about with Artificial Light?

Now that you understand photosynthesis in much greater detail and you realize why it matters so much, you’re going to be a lot more conscious about how much light your indoor plant gets. After all, you recall how I mentioned before that the quantity of light matters when it comes to inducing photosynthesis. That has you curious then, can a houseplant photosynthesize in the dark?

Yes and no, but mostly no. Allow me to explain. With no light, the houseplant can’t use carbon dioxide to make oxygen. That said, some houseplants will continue combusting glucose even without any light. This process is like reverse photosynthesis, in that the plant needs oxygen but releases carbon dioxide.

Also, whether your houseplant will stop photosynthesis completely when in the dark depends on the species of plant. Some snake plant species will continue taking in carbon dioxide to produce oxygen even if they’re in the dark. This is partly why snake plants can remove toluene, xylene, and formaldehyde from the air so efficiently. It’s also one of the many great reasons to grow them indoors.

Now, darkness doesn’t only come at nightfall, of course. If you put your houseplant in a dark or dimly lit environment, then it doesn’t matter if it’s day or night. Photosynthesis will rarely occur in this plant, which could quickly lead to its downfall.

What if you use another source of light for your indoor plant besides the sun? Artificial lights or grow lights are a very popular option for indoor plants. That’s just fine with your houseplant. As we said in the intro, your plant isn’t too picky about the light source they get. Whether it’s real and natural or artificial is less important than the strength and quantity of the light the houseplant receives.

Is Photosynthesis Affected by Season?

Yes, without any help from grow lights, with just the daylight shining on your plant, photosynthesis will most certainly be affected by the change in daylight length and intensity from season to season.

As the calendar year goes by and the seasons change, will your houseplant retain its ability to photosynthesize? Outdoor plants are far more at the mercy of the seasons than indoor ones, but that doesn’t mean your indoor plant doesn’t notice the seasons as they pass.

I’ll use winter as an example. The days are shorter, so there’s less sun to go around. If you had a plant you were growing exclusively outdoors, it would photosynthesize less because it can only do so when it has sun. Luckily, an indoor plant is not so restricted. You can let your plant take in sunlight when it’s available during the day. Then, just before the sun disappears, you can augment your houseplant’s light needs with an artificial light source. This won’t slow down its photosynthesis.

I often include the far away lands a particular plant is native to so you’ll have a rough idea of the conditions the plant would ideally thrive in.

Interesting Fact

Related Questions

Which windows are best for plants?

If you look at all the windows in your home, apartment, or office, you notice some get more light than others. You don’t want to cut off your houseplant’s supply of sunlight, so which window should you put them by?

While it can vary, southern-facing windows are a pretty safe bet. These tend to get the most bountiful and consistent sun, which is ideal for many houseplants. Just make sure if your plant is prone to burning from sunlight that you don’t leave it by the window all day!

Is light through a window considered direct sunlight?

Direct light, indirect light, dappled light…all the lighting requirements of houseplants can make your head spin sometimes. If you kept your window closed but put your houseplant on the sill, is the sunlight they’re receiving considered direct light?

No, it’s not. The light will be first diffused and then reflected through the glass before it reaches your houseplant. It’s not as intense as direct light through an open window, then. Interestingly, light intensity may be lessened by as much as 50 percent in some instances.

This isn’t always a bad thing. Your houseplant can still photosynthesize, plus the reduction in light intensity can help reduce the likelihood of the plant scorching from too much sun.

Fred Zimmer

I'm a lover of plants, animals, photography, & people, not necessarily in that order. Currently, I'm focused on photographing indoor plants & chachkies. I write & rewrite articles about creating an environment where indoor plants can thrive. I'm good at listening to music but bad at shopping to muzak.

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