matching light to houseplants, with house plant journal’s darryl cheng

THE DAYS are getting shorter, and in my Northern garden, they’re growing cooler, too. I know my houseplants will be screaming soon to come back inside, and then screaming all winter about the less-than-ideal conditions I’m offering, and how they’d like me to do better, please.

Darryl Cheng does better, using all the technical insights he can to make more than 100 houseplants feel at home in his Toronto condominium. But he also accepts that his place is not a conservatory or commercial greenhouse. It’s not perfect.

Darryl is better known on Instagram as @houseplantjournal, and as one of his 620,000 followers, I can say I enjoy being treated to his frequent posts, showing off his latest insights from ambitiously growing a condo-full of diverse houseplants. He began sharing his earliest houseplant adventures on Tumblr in 2013, and has grown his audience and more, more, more houseplants exponentially ever since. He’s the author of the book “The New Plant Parent” (affiliate link), and creates the popular website, houseplantjournal.com.

Plus: Enter to win a copy of his book by commenting in the box near the bottom of the page.

Read along as you listen to the Sept. 13, 2021 edition of my public-radio show and podcast using the player below. You can subscribe to all future editions on Apple Podcasts (iTunes) or Spotify or Stitcher (and browse my archive of podcasts here).

light and houseplants, with darryl cheng



Margaret: I was so glad that we got to do, earlier this year, the “New York Times” garden column together in spring, when I was taking my houseplants out for the season. So as I get ready to bring them in, I-

Darryl: Time flies, really. Doesn’t it?

Margaret: It does. So I’m right now reciting to myself, as I need to bring them in, some of your wisdoms and philosophy that you shared. Especially one thing which you said to me, “Plants will grow in the shape of your light. The way a plant looks is not just because of your good care, but the environment you have.”

So it’s all about the light, huh?

Darryl: Yeah. When I look at them, I use my engineering mind. I look at it like it’s a little solar-powered sugar factory. I mean, at the heart of photosynthesis, that’s really all it is, right?

Margaret: Yes. And so the same plant, the same variety, even a division of the same literal plant grown in your house, in my house, or in the commercial greenhouse where maybe it originated years ago, it’s going to look different [laughter].

Darryl: Absolutely. Yes. And the really, I guess surprising thing, I would say, is that the actual amount of light that is collected in various places between different people’s homes is actually so varied. And I think a lot of times, I mean, we know for a fact that there’s more light in the greenhouse. We know for a fact, if you have huge south-facing windows, in the northern hemisphere, you’re going to get more light.

But we don’t often, or rarely would we ever actually collect all that light and measure out the DLI, the daily light integral, on them. And I’ve been fortunate enough to actually run a few experiments, where I put light sensors in my condo, in my parents’ condo, in a friend’s condo for a couple of weeks at a time. And really, actually learned that the light varies in tenfold differences.

Margaret: In the same place, or among those several places?

Darryl: So between the different places. Well, so basically, if you don’t mind, I’ll just go right into the little experiment that I’ve been doing.

Margaret: Cool, yeah.

Darryl: I have two, what are called quantum sensors. They measure the PAR, the photosynthetic active radiation. And they have the ability to log the data. I set it to log every five minutes. So if you imagine, you have a little light sensor placed in the room and you just let it sit there for two weeks, then daily, it’ll just capture the amount of light that’s collected. And the reason I have two of these is because I usually do two at a time. So one is close to the window, one is far from the window.

And that way, when I look at the data, looking at the graphs, then I can see between the changes in weather patterns, but then the overall trend between the difference between close to the window and far from the window. And the difference is drastic, and just totally surprising.

And it’s almost like for me, because it’s so clear to me because I have the numbers, my take-home advice is:

If you have houseplants, they need to be as close to the window as possible.

Margaret: [Laughter.] Yes, they do. They do. They do. You mentioned you have this engineer brain. And what I loved is that, when we got to know each other a little bit this spring, even though I think you began getting serious with the houseplant hobby, it’s not even 10 years ago, is it? Isn’t it in the last 10 years, or something? But you availed yourself of these tools. Now, you’re talking about a sophisticated one, these PAR meters. Is that right?

But even a basic light meter, one of the light-meter apps on a phone, on a cell phone. You have a chart on your website, on houseplantjournal.com, that talks about the amount of light as relative to certain plants’ needs.

And I mean, the labels of plants say things like, “Bright, indirect light.” Or “medium light.” And that’s not data. In my house, your house—what I think is bright is going to be different from what you think is bright, right?

Darryl: That’s right. It’s all about being concrete. We talk about the scientific method: something has to be repeatable. So when I say to somebody, “It’s a medium light,” or something like that, it means nothing to them. What are you supposed to say to that?

But I will contrast that to outdoor gardeners, and their designations for light actually makes sense. Like full sun, I mean, casually, we might think, “Oh, O.K., well, the sun is shining on it.” Well, no, no, no. The real definition is six or more hours exposed to the sun.

And the reason I really like the outdoor metrics is because they are all based on the singular metric of hours of sun exposure. And so once you have that metric set in stone, in terms of what you’re talking about, in terms of what’s different, then the categories—meaning full sun, part sun, part shade, and then full shade—all of these categories actually make sense, because they’re all aligned on the same metric.

But indoors, it’s like the Wild West, because who has exactly the same obstructions? Who has exactly the same size windows? Who has exactly the same size window treatments that change the transmission of light? It’s all so different. And the reason I always advocate for measuring is because then the measurement takes into account all of these variables, and just gives you a number.

Margaret: Right. If we were getting started, if we all… Again, a lot of the people listening are gardeners, they have outdoor space. I know you have a balcony, and I want to talk about that in a minute, about some of your outdoor experiments this year on your balcony—which I love, by the way.

But if we’re just getting started and we’ve never measured the light, and we’re still at the stage, like most of us are with like, “Well, I’m going to put it near the window. It’s kind of bright indirect,” that kind of vague, generic stuff. So what meter, what gear, where would we start? Probably not with the sophisticated tools you’re talking about using in your experiment.

Darryl: Right. I mean, the sophisticated tools, I would say that the reason I’m using them is because let’s imagine… I usually do this with a presentation and it’s visual, but let’s visualize this:

The idea of resolution, like in a photo, if you have 3000 pixels by 3000 pixels, well, then the picture will be pretty clear, and you could probably print it to a certain size.

But imagine if I only had 100 by 100 pixels, then at some point, a lot of details would be lost. And then imagine if I really went just crazy and just said 10 pixels by 10 pixels, then you could barely make out any kind of detail.

So the point of getting the really sophisticated instruments is so that I can develop the most clear picture of what light really behaves… how it really behaves indoors. And then that way, I can inform a much better vague kind of guideline.

And again, I already said that guideline, which is put your plants as close to the window as possible. And I guess the secondary part of that is accept that people who have bigger windows and less obstructed windows will simply have better-growing plants. And that’s just the real-life hard truth about it.

Margaret: Yes. Yes.

Darryl: Anyway, back to the… Now, we come to this realization and now you’re saying to yourself, O.K., now I really want to get a number and understand how to measure, so that I have better expectations for whether my Ficus is going to actually grow taller, or if it’s going to stay the same for a couple of years.

So I would say if I was to break down how to measure light, if you’re going to start with a light meter, any light meter will do, even on an app. I mean, they’re not all very accurate, only because the hardware on different phones is very different.

Margaret: Ah!

Darryl: And trust me, I’ve tried this. I have a lot of developer friends, and so we’ve tried already building an app on Android.

And we realized that as we installed the app on different phones, that all different phones, and especially on Android, have completely different sensitivities on their light sensor. And the purpose of a light sensor on a phone is not to measure light, it is only to tell the automatic screen brightness how bright to make the screen. When you think about that, that’s the reason why they don’t need such precise…

Margaret: I see, I see. So if I were looking for a light meter, am I looking at a photo department, or I’m looking for a light meter? I mean, just so that I know, and I know you have some things on your site. You have a shop, and I don’t know if you have a light meter. But I just wondered, is there anywhere I should seek one, or which one?

Darryl: Even on Amazon, or photography shops probably have it, too. Although photography light meters, the reason why old-school film cameras needed external light meters, was because in the day, the technology on the camera itself wasn’t that great.

Margaret: Right. The metering wasn’t…

Darryl: Exactly. So nowadays, the camera itself meters its own light completely fine. It doesn’t need an external light meter. So in that sense, a light meter, like the photography one, might be a little bit antiquated. Even if you just look up light meter or lux meter. Then you’re going to start getting into the kind of light meters that are readily available.

Margaret: Perfect. You just reiterated your philosophy about light in the post you did on Instagram about a Sansevieria, a snake plant or mother-in-law’s tongue, or whatever. And you said: “You won’t achieve nursery-level lighting, but you can learn to love and accept different leaves.”

And people may have seen in the houseplant department of their nursery, they may have seen a Sansevieria. And it may be, I don’t know, 18 inches tall, or whatever. And then they may bring it home and a few years later, if they still have it, it may be 3 feet tall. And it’s not just because it’s an older plant, it may be because it’s not getting as much light, right [laughter]?

Darryl: Right. Right. And I think this is actually an important point because now that, for example, I know the reason those leaves are thinner, now I have to say to myself, “Do I still love the plant?” And I mean, it’s perfectly fine to say, “No, I don’t like it anymore,” right?

Margaret: Right.

Darryl: But what I’m saying is that instead of the first advice being like, for example, I could have posted that picture and said, “These are the skinny leaves that grew in my house. Therefore, it got too little light.” And that leaves the reader thinking, “Oh, then I always have to strive for nursery-level lighting. I always have to go for getting grow lights all the time.”

But no, no, no. I’m saying that this is the light level that gets in the nursery, 5,000 foot-candles roughly for the whole day. This is the level it gets in my home, 100 to 200 foot-candles. And this is the result. So now, are you O.K. with it? I’m leaving it open to people.

Margaret: Right. I mean, and what you just said, the numbers in that greenhouse nursery ideal environment, where they’re propagating thousands of plants to sell, and so forth. 5,000 foot-candles. And then in your home, 100 to 200 foot-candles. And yet, you’re growing over 100 plants. Do you know what I mean? We have to love the leaves we’re with [laughter].

Darryl: Right. And also, I also think about in terms of, even if I analogize it to human growth, a child is a rapidly growing human, especially when they get to teenager. But once you’re an adult, now I’m an adult and realizing that, well, I don’t need to eat as much as I used to. So when I think about the food that I used to eat and the amount, well, nowadays, I can’t even eat that much.

And my activity, physical activity, is all different. I used to play floor hockey a lot. I can’t play it as long (although because of COVID, I’ve stopped). But you feel all different. And so we automatically know for humans, we wouldn’t say, “Well, I used to eat two big Macs and I felt fine, but now I don’t.” [Laughter.]

Same with plants. In the nursery, they are working with a plant in a very specific life stage, because they’re buying it as a product and wanting to raise it to a certain, quote-unquote, sellable level. And then after that, it’s like the plant has reached its adulthood. So we don’t need to grow it to that degree in our homes.

I mean, realistically, what we’re doing in our homes is just letting it live out the rest of its life as nicely as possible.

Margaret: Yes. And again, there’s a great chart on your site, about the foot-candle ranges that different species of houseplants can adapt to. And it’s quite shocking. Some are more adaptable than others, and who’s who. Again, all those generic terms that we think of. Oh, this is a low-light plant. This is a bright, indirect light plant. It goes way past that.

You have some artificial lights, I assume, in your space. Yes?

Darryl: Oh, yes. I have lots of artificial lights.

Margaret: Are most of them LEDs, or what’s kind of-

Darryl: They are all LEDs, and most of them are usually supporting some growth of some plants. There are some that I would say are just ambient ones that are just above the, quote-unquote, low-light plants, to just give them a boost for the rest of the day, because they may be a bit farther from the window.

And then I have other ones that are more specialized, that they house that plant exclusively. So some of them are far into my living room, and I just turn them on when I wake up, and turn them off when I go to bed.

Margaret: So certain plants have a special light, so that that plant can live in that space in your home, to augment and give it a special light for an individual plant.

Darryl: That’s right.

Margaret: Are some in cases and stuff, or some sort of shelving units, or cases that have lights within them?

Darryl: Oh, yeah. So I do, I think it’s a very popular thing on Instagram, the Ikea Greenhouse Cabinet [above].

Margaret: Yes.

Darryl: So I have the tall, white one. And normally, it has glass shelves, but I’ve taken that out and replaced it with a kind of wire grid. So it’s more modular to move the shelves around. And yeah, there’s grow lights installed inside that, and they’re all on a timer. So everything’s nice and automated, and all I got to do is water them. [Some of Darryl’s modifications.]

Margaret: Yeah. I loved, I think it was even maybe this week, maybe just a couple of days ago on Instagram, again, you showed the results. And this is what’s so great, if people don’t know your work, is that not only are you working from data and measuring things and so forth, but you’re also doing these photographs, like the before, during, and after photographs. You’re doing it like each one is a scientific experiment.

And I don’t mean to make that sound cold and calculated, like you don’t love these plants, because I know you totally…they’re companions to you, like all my plants are to me; that you love them, and it’s not just the science.

But you had this Pothos, ‘Marble Queen’ I think, that you had given a space out on your balcony this summer, and you show what it looked like, both the difference coloration and the growth and so forth, indoors versus outdoors, right?

Darryl: Yeah. I would actually say that, well, I mean to me, experiment doesn’t sound too cold. But if anyone wants to think about it a bit more warmly, I would think about it like just think of the warm feeling you get when you watch little pictures of your puppy, when it was a puppy and it grew up bigger and bigger and bigger. And it’s like you can see the progression. Same with children too, right?

Margaret: Right.

Darryl: So when I do that with my plants, that’s what I’m looking at, which is not only is it visual proof of what happened, like a documentation for an experiment. But it is also me reminiscing like, “Oh, look, when this guy was so small. And look how big it’s gotten.” That’s what I do with the photography.

And I would say that today’s day and age, with social media and literally everyone… Actually, not even with social media. Let’s just say by the fact that we all have very high-quality phones, with good-quality cameras on them, it means that we’re in an age where we can document anything. And I think gardening is one of those things that would really benefit from a shift in the documentation.

Because I think for decades, we could only read words about how to propagate something, or what light is considered good, or position in the house, and stuff like that. Because before, if you just took it with a film camera, you wouldn’t think to just take a picture of literally everything going on with your plant. But now we can, and so I do.

Margaret: And so it’s record-keeping, and it can also be diagnostic and so forth.

Darryl: Oh, yeah. For sure.

Margaret: It can help. And you do consulting. I know you have appointments available on your website, where if people are having problems with plants, or need some houseplant advice, you do consulting virtually and so forth, which is great. And by email as well, where those photos really come in handy.

So I just want to ask, again, like I said at the beginning, even though you just have the balcony, you don’t have a big outdoor garden area where everybody goes out for the summer. But we’re coming to the lower-light season, the naturally lower-light season. In these last few minutes, do you change any of your other care tactics?

Did you stop feeding? I mean, are you backing off with watering a little bit? Is there anything else that goes on for you, when we get to the lower-light season? Again, because I know you’re using artificial lights for some, but I was just curious.

Darryl: Yeah. Actually, I prefer to think of it this way, which is that when I consider my approach to watering, it’s never an active decision of scheduling it. Rather, I would say it has always been just by looking at the soil, which implies that I have to constantly check my plants. Which hopefully, if you love your plants, you are looking at them every day [laughter].

But what I mean is, so yes, I probably do water a little less frequently in the winter. But I would say that if you’re approaching watering with just the mindset of, “O.K., this is a plant I water when it’s completely dry. This is another plant I water when it’s about halfway dry,” then you’ll reach that halfway-dry point—it’ll take longer in the winter. And so I don’t actively think about that. It just happens that way.

Margaret: Based on observation, you’re taking the cues from being in touch with your plants regularly, watching them, like a gardener does in the outdoor garden as well. We’ve got to be in touch with it. We’ve got to watch for clues of pests, of needs that the plant has, and so forth. Clean it up, groom it.

Darryl: Absolutely.

Margaret: Yeah. I know you’re a good groomer, taking off those dead leaves or the faded leaves [laughter].

Darryl: Yeah, yeah. Hey, I like nice looking plants too. But I just also decide to share the fact that yes, this leaf turned yellow. Yes, this tip turned brown. And because of the aesthetic quality of the plant, I decided to cut them off. But I’m not going to act as if it never happened.

Margaret: Right. Magically, your plant looks perfect, 365 days a year [laughter].

Darryl: Yeah. And I think quite often with social media, when we depict our spaces, we almost always want to present the best, which is, I mean, that’s understandable. But I mean, I don’t want to ever hide the fact that that has happened, because I think there’s a lot of maybe stigma—I don’t know if you’d call it stigma. But we look at any imperfection on a plant, and we start to blame ourselves for it.

But things happen, just like skin cells fall off your body, hair falls off your body, it’s the same as the cycle of nature. So we can’t put all the onus on our own skill.

Margaret: Right. And striving for some kind of unrealistic perfection, ideal kind of thing is just going to be disappointment oftentimes.

Darryl: For sure.

Margaret: Well, Darryl Cheng, @houseplantjournal and houseplantjournal.com, and author of “The New Plant Parent.” And I’m so glad to talk to you again. I hope we’ll make it a regular thing, because I always learn so much from you. And as I said, I really look forward to seeing your adventures and your experiments on Instagram. So thank you, Darryl.

Darryl: Thanks, Margaret. It’s a pleasure speaking with you.

(All photos from Darryl Cheng’s House Plant Journal website or Instagram.)

enter to win a copy of ‘the new plant parent’

I’LL BUY a copy of “The New Plant Parent” by Darryl Cheng for one lucky reader. All you have to do to enter is comment in the box below, answering this question:

Is there a houseplant you have done the best with in your space, that’s really happy living with you, and/or another that has just sulked (or worse) in the light conditions you can offer it? Do tell.

No answer, or feeling shy? Just say something like “count me in,” and I will. But a reply is even better.

Good luck to all; I’ll pick a winner after entries close at midnight Tuesday, September 21, 2021.

(As an Amazon affiliate I earn commission from purchases.)

prefer the podcast version of the show?

MY WEEKLY public-radio show, rated a “top-5 garden podcast” by “The Guardian” newspaper in the UK, began its 11th year in March 2020. In 2016, the show won three silver medals for excellence from the Garden Writers Association. It’s produced at Robin Hood Radio, the smallest NPR station in the nation. Listen locally in the Hudson Valley (NY)-Berkshires (MA)-Litchfield Hills (CT) Mondays at 8:30 AM Eastern, rerun at 8:30 Saturdays. Or play the Sept. 13, 2021 show using the player near the top of this transcript. You can subscribe to all future editions on iTunes/Apple Podcasts or Spotify or Stitcher (and browse my archive of podcasts here).

  1. Lee Ralston says:

    I don’t do well with most house plants but I have a spider plant that is six years old and doing great. It hangs in front of the kitchen window and seems to like that location.

  2. Mel Davison says:

    I love the moss posts for the pothos to climb! Great idea which I’m going to try. I’m hoping the moss in my lawn will suffice!

  3. Carol Ringo says:

    My clivia miniata, about 10 years old, has only bloomed twice: the first time, when it arrived from White Flower Farm, and again about 5 years ago. There are now 2 plants in the pot. The original plant looks very healthy but the “new” one looks sad and a bit droopy. Sitting in an east-facing window. So this is the plant I lust over, for the blooms it fails to produce!

  4. (Another) Margaret says:

    My absolute favorite is my Angel Wing Begonia. It lives inside during the winter (Appalachian Mts) and on my front porch to bloom in summer! And it happily shares cuttings with friends and family.

  5. Lisa says:

    My favorite plant is an 8-foot tall variegated ficus grown from a 5-inch tall plant purchased from a grocery store when traveling for work years ago. I had purchased the plant to make my hotel room a little more homey.

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