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Calatheas are actually pretty easy to sort out light-wise:
Bright rooms: put your Calathea somewhere where it won’t get direct light (or only gets direct light in the morning)
Dark rooms: put your Calathea in the window
No windows: 16 hours of day under a weak grow light (i.e. one with a USB connection).
Bright rooms usually have south/west-facing windows, dark rooms usually have north/east-facing. In the southern hemisphere, north and south are switched, but (I think) west and east stay the same).
If you’re not sure if it’s getting direct light, wait until you can see shadows on your walls. Direct sun will cause a really crisp shadow, but fuzzy shadows are fine.
The easiest way to determine the kind of light a houseplant needs is to look up where it lives in the wild.
You need to take into account location, climate, plus how it grows – a plant that grows at the top of a mountain in Chile is going to have different requirements than one that grows in the rainforest in Brazil.
Calathea aren’t climbers, and they live in tropical rainforests.
They grow below the rainforest canopy, so won’t receive very much direct light at all. They might get bright, albeit dappled light for a few hours, but they’re not going to be baking all day.
It can be tricky to provide for plants that grow in the undergrowth (unless you have a LOT of plants), because it’s hard to recreate that dappled effect, but Calathea aren’t actually that picky about light.
Can Calathea grow in low light?
All plants need some light to grow, and it’s a myth that Calatheas need low light. They’ll do ok in lower light levels, but I don’t think many plants do well in anything less than medium light.
Whilst it may appear that Calathea are getting low light in their natural environment, remember that most times, a shaded area outside often gets more light than a bright area inside.
Our eyes aren’t actually very good at judging light levels, but in general, the rainforest undergrowth receives more light than a medium-light area in your home.
It’s not so much that Calatheas want lower light levels, it’s more that they’re intolerant of a tonne of light.
Aaaand remember that low light levels bring a whole host of other issues, like the soil staying damp for too long and the increased chance of dust, which will attract spider mites.
I think that growers always put ‘low light loving!’ on Calathea labels, because our brains associate that with easy-care, which Calathea are, er, not.
My Calatheas grow in bright, indirect light bordering on medium light. They’re on a bookcase about 10 feet from a north and a south-facing window. The bookcase is on the west wall, and the windows are the length of the wall, so it’s getting no direct light at all.
Can Calathea grow in bright light?
Calathea can grow in bright light. Like most plants, they’ll burn if they’re not acclimated properly.
When we acclimate plants, we bring them into brighter and brighter light over time. As the light increases, the plant will produce compounds that basically work as an SPF, which will stop them burning. Move them too quickly, and they won’t be able to produce the compounds fast enough, leading to burning.
Calatheas like diffused light, so as long as you protect them from the sun with, for example, a sheer curtain, they should be fine in pretty bright light.
The problem with keeping plants in bright light is that it can affect things like water retention in soil (the closer to the light the plant is, the quicker soil will evaporate) and can also result in lower humidity
Calathea do NOT like to dry out and low humidity will quickly cause crispy brown leaves. If you're the kind of person that loves to pay a lot of attention to your plants and are happy to get a humidifier, then go right ahead. Your Calathea should grow pretty well in bright, diffused light.
If you’re more hands-off, keep your Calathea further away from the window.
Can Calatheas grow in direct light?
Calatheas CAN grow in direct light, but I don’t think there’s any point to doing so.
Calatheas are unlikely to come into contact with a tonne of direct light in the wild, because they’re protected by the rainforest canopy. Any light that filters through will be, er, filtered.
Climbing plants like Monstera have the ultimate goal of getting a TONNE of direct light, so as long as they’re acclimated, more light is better.
Calatheas don’t climb. They’re designed to get really big and bushy with long hours of diffused light.
If you take a really, really, really, long time to acclimate your Calathea, it will grow in direct light.
If you whack it outside on a sunny day and it burns to a crisp, it can start regrowing again as long as you keep the soil moist and the humidity high.
You’re quite likely to end up with a Calathea that produces pure white leaves, or at least leaves that are pretty heavily bleached. If you manage to acclimate it without burning the leaves, the colour will fade.
Aaaand since the only redeeming feature of Calathea is their beautiful, colourful patterned leaves…I wouldn’t recommend it.
How do I know if my Calathea’s getting enough light?
Calatheas that aren’t getting enough light tend to look a bit limp, sad, and yellow.
However, it can be difficult to pinpoint why a Calathea is looking sad, limp, and yellow because that’s…kind of their default state.
If you're worried that your Calathea isn't getting enough light, then first check that the roots are healthy and the humidity is ok (anything over 55% is fine), and it's pest-free. Then increase the light and see if it improves. Move it close to a north or east-facing window or five or so feet away from a south/west-facing window and see if it improves.
This is massive generalisation, but I’ve found that when people worry their plant isn’t getting enough light they’re usually right, because people tend to underestimate the amount of light a plant needs.
How many hours of light do Calathea need?
There’s no one answer to this – it depends on the amount of light, which varies a tonne depending on where you are, the weather, the time of year etc etc etc.
In the wild they’d get around 12 hours of bright, diffused light a day, depending on the time of year.
Here in the UK, we’d have to up that to around 16 because the sun’s farther away.
In winter my Calatheas probably get 9 hours of light (if you can call it light) which is sufficient for them to not die, but they don’t really grow either.
In my experience, most plants that like medium/lower light levels come from the rainforest floor which gets dappled light for long hours. So a north-facing window that gives long hours of crap light is better than a bright but sheltered window that gets awesome light for an hour or two.
Can Calathea grow with LED light?
Yes, and you don’t need fancy grow lights. I’ve tried my Calathea under my Mars-Hydro lights and they’re fine if the lights are dimmed, but it’s kind of a waste.
A Calathea will do fine under a regular LED light that’s on for a long time. It might not grow enormous, but…it’ll be ok. They also like those cheap Amazon grow lights. In general, any light that can be powered by USB isn’t going to provide very bright light, which is perfect for Calathea.
With a lot of houseplants, if you give them plenty of light, everything else sort of…falls into place. They’re better able to fight pests, diseases, and root rot, and will grow faster and stronger.
With Calathea, not only are they not that picky about light, but they actively don’t want a tonne of direct light.
I know it sounds complicated, but when it comes to light, Calathea are happy in a bright room in a spot that either gets no direct light or only gets direct light in the morning. If you only have a dark room, put it next to the window. If you have no windows, put in under a cheap grow light for 16 hours a day.
Now that the light is sorted, you need to work out humidity, water quality, and how to keep the soil evenly moist but never let it waterlogged. Oh, and be on constant alert for spider mites. Good luck! You’ll need it!