How Do I Know if My Plant Is Getting Enough Light?
How Do I Know if My Plant Is Getting Enough Light?
When somebody asks me whether their plant is getting enough light, one of the first things I want to know is where they have it sitting. What direction does the window face? How far away is the plant? Are they using plant lights? Because those details make a tremendous difference in how much light is actually reaching the leaves.
I think lighting is one of the most overlooked parts of growing houseplants, and it's connected to so many of the things people struggle with. How quickly their plants dry out, how often they produce new leaves, how large those leaves become, and how well the roots develop are all influenced by the growing environment.
And the nice thing is that once you understand the light you have available, you can make adjustments that help support the plants you're growing.
Let's Start With Your Windows
If you're using natural light, the direction of your windows gives us a good starting point.
Here in Michigan, an east-facing window brings in that morning sunlight, while a west-facing window receives stronger afternoon light. South-facing windows can provide some wonderful growing conditions, especially as we move into the shorter days of the year. North-facing windows generally provide softer light, which can be useful for certain plants depending on their needs.
Now, where is your plant sitting in relation to that window?
You might have a beautiful south-facing window with a plant sitting five feet away from it. If you move that same plant within a foot or two of the window, the amount of light reaching those leaves can be considerably different.
This is something I wish more people would experiment with because sometimes the adjustment is as simple as changing where the plant sits.
I generally like to begin within one to three feet of an appropriate window for many of our tropical houseplants, and then evaluate how much light is actually reaching them. The strength of the sunlight, the plant you're growing, and anything outside that might be blocking the window are all going to influence that placement.
You can have two windows facing the same direction and get very different results. A large tree, a covered porch, or even the size of the window changes how much light comes into the room.
How Much Light Is Actually Reaching Those Leaves?
This is where I really like using a light meter.
You've probably heard me talk about foot-candles during my Lives. Foot-candles measure light intensity, and they give us a way to evaluate the light reaching our plants.
Let's say you've got a plant sitting three feet away from a window. Take a measurement at the leaves. Then move your meter closer to the window and take another reading. You can see how much the intensity changes just by moving a couple of feet.
If you're growing with natural light, try taking measurements throughout the day. Your morning reading may look completely different from your afternoon reading, especially if your plant receives direct sunlight during certain hours.
That gives you a much better picture of the light available in that location.
And remember that plants use light over time. Both the intensity and the number of hours they receive that light influence photosynthesis and growth. One foot-candle reading tells us what's happening at that particular moment, so I like looking at those measurements along with the plant's overall development.
Different plants have different lighting requirements, and that's why understanding the particular plant you're growing is important. Some will develop beautifully in moderate light, while others need considerably higher intensity to support the growth we're hoping to achieve.
Growing With Plant Lights
At Rooted Plant Shop, I grow entirely under plant lights. I have three north-facing windows, and the natural light coming through those windows isn't enough to support the variety of plants I grow. My plant lights allow me to provide more consistent lighting throughout the shop.
At home, I use both my windows and supplemental plant lights. Some of my plants receive plenty of natural light, while others need additional lighting to support their growth.
I generally recommend full-spectrum plant lights in the 5,000K–6,500K color-temperature range, and I typically run my lights for twelve to fourteen hours a day for many of the tropical plants I grow. The strength of the fixture and how close it's positioned to the plant determine how much light is actually reaching the foliage.
This is an area where I see people struggle quite a bit. They have a plant light, but it's positioned so far away from the plant that the amount of light reaching the leaves is fairly low.
I like my lighting positioned over the canopy, where the leaves can receive it. As the plant grows, I adjust the fixture so the light continues reaching the developing foliage.
And this is another place where a light meter can be really helpful. Take a measurement with the light at its current distance, then make a small adjustment and measure again. You'll begin seeing how the intensity changes depending on where that fixture is positioned.
Just be mindful of how close you're bringing the light. Depending on the fixture, increasing the intensity too quickly can cause leaf damage. Giving the plant time to acclimate while you make those adjustments is helpful, especially if it has been growing under lower light.
Your Watering Can Help You Evaluate Your Light
Another thing I pay close attention to is how long my plants take to dry out.
For many of the tropical foliage plants I grow, I'm generally working toward a watering cycle of approximately seven days. That's a timeframe I use to help evaluate how the plant is growing and using its available moisture, while considering the needs of the individual plant.
Let's say you've got a plant that's taking fourteen days to dry out. It's sitting several feet away from a window, and you're noticing that it hasn't produced much new growth.
I'd be curious about how much light it's receiving.
You could try moving it closer to an appropriate window, or adjusting its plant light if you're using supplemental lighting. Then pay attention to what happens over the next watering cycle.
If it was taking fourteen days to reach its preferred level of dryness and now it's taking ten, you've got something useful to compare. If you're also seeing healthier new growth, that's even more information about how the plant is responding.
Of course, the growing medium, pot size, temperature, and health of the roots all influence how quickly that moisture is used. Looking at those things together helps us understand what's happening.
I think tracking the watering cycle is especially useful for people who haven't purchased a light meter yet. You can still begin observing how the plant responds when you change its placement.
Pay Attention to the New Growth
Once you've made an adjustment to the lighting, give your plant some time and watch how it develops.
Look at the newest leaves. Are they developing at a healthy size for that plant? Is the spacing between leaves changing? Is the plant beginning to produce growth more consistently?
If you're growing a climbing plant, you can also pay attention to how its growth changes as it matures and develops along its support.
The newest foliage is especially helpful because it develops under the conditions you're currently providing. Older leaves may have grown under an entirely different lighting environment.
I like taking pictures because it's easy to overlook gradual changes when you're looking at the same plants every day. When you go back and compare photographs from several weeks earlier, you can get a better idea of how the plant has been developing.
And as the seasons change, you can repeat those observations. A location that provides wonderful natural light during part of the year may need some adjustment as the days become shorter or the sun changes position.
The more familiar you become with your windows, your plant lights, and how your plants respond, the easier it becomes to find growing locations that work well for your collection.
Keep Learning With Rooted
Lighting influences so much more than where we put our plants. It affects their development, how they use water, and the growing conditions we're able to create in our homes.
I wrote The Rooted Guide to Lighting to help people understand those relationships and feel more comfortable evaluating their own growing spaces. We go further into natural light, plant lights, foot-candles, placement, and how to make adjustments based on the plants you're growing.
If you'd like to understand how to measure your light and use that information to create better growing conditions, this guide will help you put those pieces together.
