Even people with no real knowledge about biology or botany know that plants need sunlight to survive. Some even have a rudimentary grasp of photosynthesis.
But let’s face it, most people don’t really know how plants work and what will happen to them if they had to go without sunlight.
The short answer: When plants aren’t exposed to enough light for an extended period of time, they will begin showing signs, such as color changes in the leaves and a “leggy” stem.
Why Do Plants Need Light? (The Importance of Sunlight to Plants)
Plants need food for energy, just like we animals do. The only difference is that they happen to be able to make that food for themselves. It’s a chemical process called photosynthesis and it uses the energy of sunlight to create a form of sugar from water and carbon dioxide.
Without several hours of light every day, a plant will basically starve to death, regardless of how much water or fertilizer you give it.
While they are photosynthesizing, they also put out clean oxygen to help improve your indoor air quality. They’re great filters that way, so it’s a win-win situation for you to keep the light bright and your plants happy.
How Much Light Do Plants Need, and Do All Plants Need Sunlight?
Of course, the next obvious question is how much light do plants need. Not all plants have the same daylight needs, which could be why some of your plants do well and some do not even when they are all getting the same full “day” of sunlight.
Every plant is a little different, and light needs can be based on how many hours of light each day and also how bright the light is when it’s on.
Typically, most plants will need a minimum of 6 to 8 hours of light each day (sometimes bright, sometimes indirect), yet some will only thrive if they are getting 10 or up to 14 hours of light. Some really shade-loving plants will even do fine if they only get 3 to 4 hours.
There are also light amounts that are important for triggering a flowering cycle, rather than actual survival of the plant. Blooms can rely on day-length changes to time flowering for the right parts of the season.
Plants that naturally flower in the spring may be triggered by lengthening periods of light, and fall blooms are going to react to shortening days. This can be more complicated than we can go into here, but the point is that your plants will still survive just fine even if the exact day length times aren’t met. It’s just about the flowering.
On the flip side, as I cover in another article, you should be aware that plants need darkness just as much as they need light. Their metabolism is designed to make use of the night period, and they will definitely not thrive if you try to over-expose them to light, either sunlight or artificial light.
What Happens to Plants Without Light?
If you are unsure how much light your plants need, you can use their growth and appearance to judge if they are getting enough.
One of the first things you’ll see is that the leaves start to get paler, and eventually turn yellow as the green chlorophyll pigment fades without input from the sun. After yellowing, they’ll drop right off. Any new leaves that develop will be smaller or thinner than usual.
As the plant gets desperate, it naturally tries to get taller to reach the sun. That means it changes its growth to extend the stem, leaving you with tall but elongated plants, usually referred to as “leggy.” There can also be a really exaggerating leaning towards the light source, more than you usually get since most plants will develop a gentle lean as they grow.
Worried about putting your plants in too much sun? There are different signs you can watch for. The leaves will start to develop brown around the edges, and they will start to yellow. There can be drooping of the stem and leaves, even if it seems that you are watering it enough.
Plants that have gotten a little unhealthy due to lack of sun are easily treated by moving them to a brighter spot or adding new lights of your own. They will start to thrive again, and faded leaves will darken up as the chlorophyll production gets back in action.
But any elongated stems will stay that way, now that they have grown leggy. You might have to add a little extra support in the future.
Consider Artificial Light Instead
When you don’t have enough natural sunlight (or any at all), take a look at my article to turn to artificial lights instead. If you are intimidated by the idea of getting plant lights, here are a few pointers to help you out.
You don’t need fancy “grow lights” though they do have their place if you are knowledgeable about indoor lighting or have a lot of plants to take care of. A standard light that is labeled as full-spectrum is a good overall choice for most plants, and is the best place to start if you want to add more light for your houseplants.
If you want to get a little more fancy, you can make some choices about your light spectrum to perhaps give your indoor garden a boost. Choosing lights that lean to the blue end of the spectrum (aka cool lights), will help to encourage lush foliage. Red lights (aka warm) are better to trigger flowering or even fruit production.
It’s not complicated but you can just stick with full-spectrum light, particularly if you are growing different types of plants that might have different needs.
You’ll also have to decide what kinds of bulbs will work best for your space. There are usually various shades or tints available in any type of bulb currently on the market, so you’ll want to take other details into account:
- Incandescent – cheap, short-lived, produces heat, uses a lot of wattage
- Fluorescent – more expensive, long-lasting, stays cool, uses little power, comes in compact and tube form for fixture flexibility
- LED – most expensive, uses the least amount of power of all of your options
Each type of light has their place. If you can’t really decide, go with the fluorescent bulbs. They are a great mid-range option that won’t cost you $20 per bulb and they use very little electricity.
You don’t necessarily need to find true grow lights. Standard household bulbs in these formats or color tints are perfectly fine. Add a timer to ensure you’re getting the proper amount of light each day, and you should be ready to go.
Sometimes people look for green lights because they seem to “go better” with plants. This isn’t necessarily true. Plants do not use green wavelengths whatsoever, which is why that light is reflected and the leaves look green.
Best Plants for Low Light
Dealing with low light areas is tough enough, so make your life easier by choosing varieties of plants that are best suited for these conditions in the first place. Some extremely popular houseplants for less-than-sunny areas are:
- Peace lily
- Cast iron plant
- Sword fern
- Snake plant
- Peacock plant
- Spider plant
These types of plants will often do fine in any low light room, even with only an artificial room light. Pick a couple of these for the office or a dim corner of the living room. As long as the room light is on for most of the day, they’ll keep on thriving.
For a more in-depth list, see my post about the best low-light plants.
Plants to Avoid
With a little supplemental artificial light, you can have great success with many houseplants beyond just the low-light options. But if you are in a position where light is an issues, you should probably stay away from any plants that have high needs for light, unless you want to build a grow-room with banks of lights going 18 hours a day.
Even though some of these are fine indoors when you have a bright sunny window, low-light spots are not a good idea for: aloe vera, succulents and cactus, geraniums and English ivy.
With the right species choices and a few artificial lights, you should be able to keep a few houseplants growing nicely no matter how much natural sunlight you have to work with.