Elements of plant care: sunlight
Just like mammals use food for energy, plants use light in the same way. Sunlight and/or proper artificial light is the best and most important food for plants. (For the sake of length, I'm going to focus solely on natural light in this post and discuss artificial light in a separate post.) Plants need light for photosynthesis, and in case you don't remember what that is from your high school science classes, it's "the process by which green plants and some other organisms use sunlight to synthesize foods from carbon dioxide and water (Dictionary.com)." Simply put, photosynthesis is how plants convert light into energy. They collect light in their leaves and stems and roots like little solar panels! So cool, right? Plants that don't get enough light tend to stretch towards the closest light source and suffer "etiolation," which means new growth is leggy, weak, pale, small and/or twisted. Plants are very adept at letting us humans know when something is wrong, so if you see etiolation occur, move your plant to a brighter spot.
Now that we understand the importance of light, let's break down what low light, moderate light, bright light, and full light mean. You'll see these terms often in plant care books and websites, and I use them as well. The difference among these levels of light can often be confusing, especially if you're just starting out, because lighting is subjective. Low light doesn't necessarily mean a dark corner in your bathroom, and bright light doesn't mean full sun.
Let's start with low light; low light is typically the light you'd get from a north-facing window. It's a cool, ambient light with no direct sun at any time of the day. If you're not sure what direction your windows face, take note of which window the sun rises in the morning: that's east. The direction the sun sets is west, and from there you can figure out the rest! Low light can also be light that's a few feet away from an east or west-facing window. The further away from the window, the lower the light, no matter what direction your window faces! There are plenty of plants that thrive in this type of light, such as a heart-leaf philodendron like the one pictured above, pothos (Epipremnum aureum), snake plant (Sansevieria trifasciata), peace lily (Spathiphyllum wallisii), ZZ plant (Zamioculcas zamiifolia), Chinese evergreen (Aglaonema species), and cast-iron plant (Aspidistra elatior) to name a few.
Low light also does not equal "no light." If you don't have a natural source of light and aren't willing to use artificial lights, no plant life other than mushrooms or mold will flourish. ALL plants need some kind of light! There are some species like sansevierias and ZZ plants that can tolerate a very dark corner of a room, but they would merely be surviving, NOT thriving. And isn't helping your plants thrive and grow the point of having them? ;)
One of the most important conclusions I've come to in my green thumb journey is that most low light or moderate light plants will truly flourish in brighter, filtered light. Take a supposed "low light" plant and acclimate it to brighter light without direct sun, and you will be impressed by how the growth takes off! I put many of my low and moderate light plants outside in the shade this summer and they're positively bursting with new leaves and blooms. Even shade outside is going to be brighter than most windows in your house.
Moderate light typically comes from an east-facing window. Morning sun from the east is a soft, cool golden light. There might be a couple hours of direct sun, but it's not too intense and it's likely not going to scorch the leaves of more light-sensitive plants. This is the perfect location for the low-light plants mentioned above, or any plant that can only tolerate an hour or two of direct sun. Some great options for an east-facing window are English ivy (Hedera helix), arrowhead vine (Syngonium podophyllum), Monstera (Monstera deliciosa), most species of peperomia, and almost any member of the Marantaceae family (which includes maranta, calathea, ctenanthe, and stromanthe species).
Sun from the west is bright and hot for a few hours in the afternoon, so if you have some plants that call for bright light and can tolerate direct sun for a few hours, a west-facing window is perfect. In the morning, the light will be pretty ambient, but the sun will pour through in the mid-afternoon. You can always place a sheer curtain or venetian blinds over your window to diffuse the light if it's too direct. Most plants do well here, especially if there is a window cover to filter the light. Some examples of plants that need bright light are a rubber tree (Ficus elastica), fiddle leaf fig (Ficus lyrata), flamingo flowers (Anthurium andraeanum), and most dracaena and palm species.
The strongest light in your house will be from a south-facing window, and it's intense, full light that's suitable for cacti, succulents, crotons (Codiaeum variegatum), and hoya species. Basically, this window allows for almost a full day of direct sun. Most plants aren't going to be able to handle the intensity of this light, so adding a sheer curtain or blind like I mentioned above will make it an ideal location for almost any plant.
Take into account that how bright the light is from any window also depends on if there are buildings, houses, trees or other plants outside blocking the sun. For example, I have an east-facing bay window where I place lower light plants because there are maple trees in my front yard and a shrub that partially obscures the window, creating lower dappled light. You can also increase light by hanging mirrors or painting the walls bright white to reflect light, and of course, investing in artificial grow lights. Read my next post for more on artificial light, which is also helpful during winter months when sunlight becomes scarce!