Updated: Oct 17
When people talk about houseplant lighting, the simplifications range from vague to wildly inaccurate. Every time I see the phrase "bright indirect light" printed on a label and stuck into a pot of "assorted foliage" I want to grab whoever designed said plant label and whisper politely into their ear "No, please no... you can't keep getting away with this."
Now, they don't make it easy. That's my job, maybe, and part of why I started this shop to begin with. I don't expect any of you to have a PPFD meter or even know what PPFD means. I'm not even going to say what it stands for, since it'll cause more confusion than it resolves. It's like, and this is a bit of a throwback: "pen pineapple apple pen" or something, ok? Let's go with that. That's what it reminds me of, at least. Anyways, if you do have a PPFD meter, you're a total nerd. Those things cost $80 used if you're lucky. Fortunately for you, I just so happen to be a total nerd and I went and took some measurements for you, out of the kindness of my heart and the camera-ness of my phone. It was a partially cloudy Summer day in Maryland, around 80 degrees Fahrenheit. I took these photos around noon and didn't edit them. Let's start outside.
Wow, big number! What does it mean? Well, at 732, a succulent would do great. Still, get this: a fern would do great too! The truth is, there's no such thing as "too much light" and what you get indoors is likely to be wayyyyyy lower than what you'll be seeing outside. Where people get stuck tends to be the balance. "Too much light" is only an issue if you don't give your plant enough moisture to match.
To prove the "too much light" thing as a myth, I can draw from my own sights and experiences. On my doorstep, I've grown aplinia (a plant structured similarly to a calathea), Autumn ferns, graptopelatum (the traditional chubby red flower-shaped succulent), and sedum. Despite what you'd think, they all continue to thrive to this day! For further evidence, think of the "delicate" ferns you see hanging at the hardware store, happy outdoors in the bright light.
Now, let's take a quick look at the shade.
Here, the meter reads as 116. This is a huge drop down, right? Around 1/7 of where we were before, yet only a few feet away. Barriers make a HUGE difference, sometimes blocking light entirely.
Still, 116 is a lot! It's enough to make a violet or begonia start flowering.
Here's the thing, though: some plants are picky. Some plants NEED at least 500 or they'll start misbehaving. Don't worry, I'm a snitch, and I'll absolutely tell you who these troublemakers are.
The trees that hate shade
Pomegranates, lemons, limes, and olives: basically anything with fruit. They'll throw a total tantrum if they aren't getting the light they want. It's annoying, because they drop their leaves all over the floor, sometimes killing themselves in the process. If your plant did this, move it to the sun just in case. It might bounce back.
The picky succulents
If you've got a succulent in a pale or yellow color, chances are: it wants bright light. It'll stretch itself, reaching for more if you don't give it what it needs. The space between leaves will get longer and longer as it reaches for the sun. Succulents that need bright light to look cute include echeveria, graptopelatum, and sedum. Succulents that don't care as much would be aloe, ox's tongue, and haworthia. If your succulent's already stretched out, the best thing you can do is to take a few leaves out, lay them on a pot of soil outdoors or in bright light, and wait for the babies to grow. Just like new!
Fruits and herbs
I felt really sad when my friend was set up with his first set of apartment houseplants. He was given a tomato and basil, for his dimly lit windowsill. They stretched out desperately, reaching for light as whiteflies dined in on an easy target. The thing is, even in a bright window, these plants won't taste right. They need a full spectrum grow light, producing the UV light that the window glass blocks out. UV light is what plants use to generate certain chemicals: chemicals that help with color and flavor, as well as pest resistance. If you want food indoors, you should really consider a grow light. Unless it's sprouts, then just go to town and do whatever.
Ok, so now we go inside, finally, right? Thank goodness, I'm safe from the mosquitos now.
63 isn't amazing, but it's definitely enough for a non-picky plant. For most plants, 40 is the minimum for growing steadily. Throughout the day, this number is gonna change a lot. It might even reach 1,000. Now, be careful, here. It's not the light that'll cause issues, but the heat. You can get a plant crispy if you start baking it. Touch the window or the sill if you're worried, before putting the plant there. Do this at a really sunny time of day. Cold can cause issues, too, so be careful, and for goodness' sake, don't be like me, and don't leave a plant in a hot car!
Notice, how I said the light changes, just in the span of a day. There's another myth busted! I'm like, the mythbusters of plants or something. Gimme a show and tons of money, thanks. Anyways, yeah, plants do not care about a sudden change in lighting. They do not need to be acclimated. It's ok. Leaving the lights on all night would hurt your plant, actually. They can tell when the light is gone and they use that time to do specific plant activities in their plant routines. Let them sleep!
Ok, so, let me take a couple steps back.
You see that? With a single step, we went from 63 to 38, then with a second step, we went down to 21. Crazy difference! This is why I say your plant belongs within a few feet of the window or grow light. Imagine the middle of the room, it's probably like 2. In fact, I've tested, I know it's like 2. Most plants would hate it, and while none would love it, certain ones would tolerate it. Pothos, nerve plants, snake plants, and ZZ plants can survive off the light from your ceiling's lightbulb. Peperomia , haworthia, ox's tongue, and syngonium could, too.
Plants are often marketed with terms like "low light", "bright light", and "indirect light". "Low light plants" and "Medium light plants" are actually low-light tolerant or medium-light tolerant. The truth is, they'll do just fine in bright light and will probably be a lot happier there, too. Just keep them watered and at room temperature.
So, now, let's talk balance.
Watering will get its own article in the near future, but in terms of its relation to light, here's the rundown. If your plant is in brighter light, it'll use up more water, much faster. This is great for preventing root rot (root rot is basically a drowning plant). This fast drying can get annoying, though, if your plant is in a small container, like an inch or two big, with no lid. You'll be watering that guy daily unless you give him some more soil, some coco chips as mulch, an enclosed container, or a spot further from the light. The truth is, a lot of the water just evaporates. When you use a terrarium or add coco mulch on top of your soil, you'll see just how little your plant actually drinks. Most plants really don't like drying out entirely. If it's wilting, it's stressed, and you should probably do what you can to avoid it getting to that point. Stressed plants release certain things with an unfortunate side effect of letting bugs know they're vulnerable. Definitely subscribe, though, because I can't wait to get into the details of watering. I've got some more myths to take care of.
So, have you ever had a plant burn in the middle of a room, at room temperature?
That's fertilizer, baby! Burns can happen when a plant has been fertilized, but doesn't have enough light. The plant gets hurt because it can't process all the nutrients. This makes the leaf tips all crispy or causes weird yellow spots, the size of Nerds candy. If the spots are brown in the center, that's a rude fungus: a whole other issue I plan on writing about. A lot of plants bought at stores have fertilizer pellets in the soil, so be sure you either give them plenty of light or take the fertilizer out. If the roots are strong and thick, you can remove the fertilizer pellets by hand. If not, you can take the plant to the sink and run water through it a few times. This will wash out a little bit of the fertilizer. You might have to use this as your watering method in general if the fertilizer is really excessive for your plant. Unfortunately, the fertilizer will continue to release into the soil over time. It's really inconvenient because it's usually the amount of fertilizer the plant would be using in the greenhouse it came from. That's way more than it would be using in an average home environment.
Now's the part where I talk about grow lights. I'll tie it into some really interesting general plant info in the end, too. Now check this out:
1457! Insane, right? Keep in mind, every foot you move away, it'll go down by around half. The amazing thing to me is that this guy was only $60. It's enough to cover an entire desk or two of plants, with amazing growth. So, you might wanna get one of your own, right? Or at least look into it. You'll see a lot of words and concepts floating around. PPFD is the one that matters.
PPFD = the amount of plant-enjoyable light in a specific spot
Lux = not that, don't use it. It only measures visible light that humans can see.
Footcandles = similar thing to lux, don't use it.
Apps that measure light = vague, inaccurate, you're better off using your eyes
DLI = the amount of plant-enjoyable light used in a day
Wattage = totally irrelevant, used to sell grow lights and make them sound fancy.
Blue/purple lights = look fancy, make your plants look purple, that's about it
A good price for a grow light = $20-$70
People will act as if the energy consumption is important, when, actually, the differences are so insignificant, they're barely worth paying attention to, unless you're on a major budget. It's $5 per month to run an industrial light 12 hours per day. The thing is, if your room has an industrial grow light in it, you won't need to run your regular ceiling light at all. If you're using a regular grow light of 40 watts or less, for 12 hours per day, it'll cost $1 or 2 per month in energy. We could go into the CO2 emissions from the energy used to power your home and, conversely, the grow light, but that's also pretty insignificant. Your plants aren't doing much carbon capture, either. If you want to help with climate change, donate to carbon capture organizations.
If you want a whole table of plants, so you're picking out an industrial grow light, I've already done the research. Go on ebay and get a VIPARSpectra light for $60.
It's the best deal I've seen for the strongest light, and they're most of what I use in-store and at home. For an entire setup, you can use an entryway coat rack/bench. This can both support your plants and hang your light, without putting holes in the ceiling. They go for around $100
Still, what if you just want one plant, or a little terrarium? You don't want the entire sun for that, right? It's
a bit of overkill. We sell these cool halo lights in the shop that I genuinely really enjoy for a few reasons. They get TALL. You can stand one on the floor if you want, but they also collapse down enough to sit on a table.
For another option, they've got a lil spike you can use instead of the platform. That lets you stick the light right into the soil, like a stake or a plant label. They look more like a cute lamp than some weird industrial panel, so they'll look nice in your room. For these, you really want it right above the plant's head, like a halo. That's how you get the good numbers. By the way, they've got a timer built in, that you can set to have it on a schedule. The plug is a USB with one of those detachable wall blocks, like a phone charger. This can be helpful if you use extension cords or multi-outlet adapter thingies.
I tested another grow light, since I had it around. This one's super common and you'll see it a lot online.
As you can see, it's not great. It's a bit of a scam, really. I don't recommend it.
Now, here's that extra spicy houseplant lore! Apologies for that previous sentence: I may or may not be finishing up this article while half asleep. In another reality, one in which I had not been hit by the sleepy, I may or may not have ended up writing something like that anyways, regardless. Still, it's definitely a transition sentence.
Ok, so, more light means faster growth, smaller leaves, and for some plants, more space between the leaves. That's how I grow string of turtles plants so tiny for the living necklaces. When they have all the light they need, plants don't need to worry about growing bigger leaves to catch more. They just go crazy and do what they want. The faster growth in bright light means the plant will need to be watered more often. Plants that can get pink or red will get a lot more pink or red with more sun. Full spectrum grow lights are amazing at enhancing these colors, as well as the flavors of herbs. Plants that get white patterns on their leaves get more white when there's more sun. This is because, again, they have all the sun they need, and don't need to waste energy, creating more green leaf space to absorb any more.
Coloration can help with plants for low light, too.
Green or dark colored plants don't need as much sun as pastel ones, because the green pigment is the part that absorbs the light. Really green plants can absorb so much sun on every part of their leaves, so they can tolerate having less sun to take from in general. They grow faster because of this, too. If your space isn't very bright, pick something dark green.
So, that's the jist of it! Super brief, I know (sarcasm). There really wasn't anything quite like this online, so, I thought I'd toss my hat in the ring (as if that's a phrase people use in this century). Hopefully, my silliness made the science a bit more fun, and hopefully, my writing as a whole makes a good amount of sense. Water's totally up next, so definitely subscribe to get that article when it's ready. Thanks, everyone, for reading this, and have a wonderful day with happy houseplants!
Much like a houseplant, my cat, Thanatos, knows how to appreciate a good sunbeam.