How Many Hours of Light Do Houseplants Need?
Grow lights and daily lighting schedules
More light doesn't always mean more growth!
When we talk about light for our houseplants, we often focus on its intensity. Do they prefer indirect light, a little direct sunlight or a less brightly lit spot?
But there's another equally important question: how many hours of light should they receive each day?
And more importantly, why not simply leave our grow lights on 24 hours a day to make our plants grow faster?
Because yes, even though our plants love light, they still need to follow their own natural rhythm!
How many hours of light do plants need per day?
For most tropical plants we grow indoors, 12 to 14 hours of light per day is an excellent starting point when using grow lights.
Some plants may benefit from up to 16 hours of light, depending on their needs and the intensity of the lighting.
Here are some general guidelines for artificial lighting:
- Monstera, Philodendron and Anthurium: approximately 12 to 14 hours.
- Alocasia, Aglaonema and Scindapsus: approximately 12 to 14 hours.
- Hoya: approximately 12 to 14 hours.
- Cacti and succulents: approximately 12 to 16 hours.
- Plants that tolerate low light: approximately 10 to 12 hours, depending on the intensity of the grow light.
Not quite sure about the difference between indirect light and direct sunlight? Check out our guide How to Choose the Right Light for Your Houseplants.
Why do plants need a period of darkness?
Contrary to what you might think, plants don't simply spend their days absorbing light and then do nothing at night!
They have a circadian rhythm, a kind of internal biological clock that helps synchronize several functions with the natural cycle of day and night.
During the day, plants use light to carry out photosynthesis and produce the sugars needed for their development.
When the light disappears, they continue to respire, grow, and use or redistribute the energy they've stored.
Periods of darkness also help regulate various biological processes, including those related to growth and, in certain species, flowering.
Why not leave grow lights on 24 hours a day?
You might think that providing continuous light would allow plants to produce more energy and grow much faster. But it's not that simple!
Constant exposure to light can disrupt their biological rhythms. In some species, it may also cause stress, leaf damage or less balanced growth.
And most importantly, a plant can't necessarily make use of all the extra light it receives.
More light doesn't automatically mean better growth!
Some plants may temporarily tolerate continuous lighting, but for most houseplants, it's better to maintain a regular cycle of light and darkness.
Light intensity matters just as much as duration!
Here's something we often forget: not all grow lights provide the same amount of light.
A small, low-powered grow light running for 14 hours may provide less light to a plant than a more powerful lamp used for 10 hours.
This relates to the total amount of light a plant receives each day, known as the Daily Light Integral (DLI).
Without getting into complicated calculations, just remember that light intensity and duration work together.
The distance between the lamp and the foliage also plays an important role. A lamp placed too far away may be ineffective, while one placed too close can sometimes damage the leaves.
The goal isn't to provide light for as long as possible, but rather to give each plant an amount of light that suits its needs.
What about our Quebec winters?
In Quebec, natural light changes dramatically throughout the seasons.
During summer, our plants can enjoy long days and abundant natural light.
But as fall arrives, days get shorter and the amount of available natural light decreases considerably.
This is often when we notice growth slowing down in many tropical plants.
Grow lights become particularly useful at this time of year because they can supplement natural light.
They help provide more consistent lighting and maintain good growing conditions, even when daylight hours are limited.
And no, you don't have to turn your living room into a professional greenhouse to benefit from grow lights!
To adjust your watering routine and other care habits during the colder months, check out our article How to Care for Houseplants During Winter.
Day length can also influence flowering
This is called photoperiodism.
In certain species, the duration of darkness directly influences the biological processes that trigger flowering.
One example is the Christmas cactus (Schlumbergera), whose flower bud development can be encouraged by long nights and suitable temperatures.
Artificial light turned on at the wrong time can even interfere with this process!
Sometimes, getting beautiful flowers simply means knowing when to turn off the lights.
What to avoid if you want happy plants
- Thinking 24 hours of light will double plant growth. Plants have their limits! Continuous lighting isn't necessarily beneficial and can even become counterproductive.
- Forgetting about the dark period. A regular day-and-night cycle helps respect the natural biological rhythms of most houseplants.
- Confusing duration with intensity. A lamp that stays on for a long time isn't automatically a good grow light. The amount of light that actually reaches the leaves matters just as much.
- Constantly changing the lighting schedule. A timer helps maintain a consistent routine and saves you from having to remember to turn the lights on and off every day.
A little note from Roxanne
Personally, I think grow lights are incredibly useful, especially when you have several collectible plants and want to provide good growing conditions all year round.
At Zarits, we know just how much light can influence plant growth, leaf size and even the colours of certain varieties.
But I also think it's important to understand that we can't speed up a plant's growth indefinitely simply by giving it more and more light.
Every plant has its own rhythm, and that's part of what makes growing them so fascinating!
My advice? Start with a schedule of around 12 to 14 hours of artificial light per day, use a timer and observe how your plants respond. You can then adjust the duration or intensity according to their needs.
And most importantly, don't forget to give them a period of darkness.
Because, after all, just like us, plants need their rest too!
