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Light Spectrums: Which Are Right for Hemp?

With hemp being federally legal and more than beneficial for our planet to grow, more and more people are starting to cultivate hemp these days. But, with this newfound popularity for hemp farming, growers quickly realized how tricky this green plant could be. This is especially true in terms of lighting.

Like most plants, the hemp plant reacts to different colors on the light spectrum differently, making it essential to understand their relationship. That’s why, today, we’re taking a look at the best light spectrums for the hemp plant and when you should use them.

The Different Spectrums & Phases

It’s important to stress that the hemp probably won’t thrive being grown under just one color on the light spectrum. If the plant were being grown outdoors and under the care of the sun, it wouldn’t be exposed to just one color, either! That’s why it is so essential for hemp growers to understand the different light spectrums and how these wavelengths affect their plants.

As your hemp plant moves throughout its life, it will go through different phases as well. Starting with germination, moving to a seedling, vegetating a bit, and then finally flowering, the hemp plant’s life cycle is a long one. Researchers have found that different colors on the light spectrum benefit the plant better than others throughout each phase.

When you’re able to properly replicate the kind of light spectrum exposures that your hemp plant would get outdoors, the yield you get will likely be much more successful. Using these specific light sources, you’re able to maximize plant growth, cannabinoid growth and cultivate an extremely healthy (and profitable) plant.

Now, let’s talk about these light spectrums.

Ultraviolet Rays

UV rays are not a part of the visible light spectrum, but they’re lights that your hemp plants sure love. For us humans, UV rays cause painful sunburns after spending too much time out in the sun. However, for the hemp plant, ultraviolet lights provide ample nourishment to trigger photosynthesis and even boost cannabinoid production during the flowering stage of its life.

Using UV lights with your hemp plant is a tricky matter, however. When growing marijuana, UV lights have been shown to increase THC levels in the buds. With hemp, you must be careful not to grow plants with THC levels any higher than 0.3%, or, according to federal law, you’re not even growing hemp anymore. While there may be ways for growers to manipulate UV lights to boost just CBD levels, this hasn’t been proven just yet.

Until then, it is best to use gentle doses of UV lights throughout your hemp plant’s flowering stage. This is the stage where your plants are developing their buds, which is one of the most valuable parts of the whole hemp plant. Paying close attention to their development here is crucial, and the right amount of UV light can help support your plants throughout this stage. Again, just be careful not to rely too much on these types of lights, as you may end up with a product you didn’t want.

Blue Light Spectrum

Blue is one of the most critical colors on the light spectrum for the hemp plant. If your hemp plants feel as if they are not getting enough blue light, they will assume bigger, better plants around them are shading them. Thus, they will start to grow up and out, much more sporadically than what appeals to hemp farmers. Sometimes, this kind of growth can even ruin a yield if you’re not careful.

During the vegetative state is the best time to subject your plants to a healthy blue light. In the vegetative state, your plant is doing the most growing. Here, your hemp will start to grow its stem, sprout some leaves, and somewhat resemble a hemp plant. To have enough energy to do such drastic growing, though, it needs ample blue light to thrive off of.

Your hemp plants would naturally be exposed to a lot of blue light during the summer months. As many farmers suggest, if you started your cultivation in spring, hemp would likely be in a vegetative state during the summer, soaking up the blue light spectrum. This is exactly why you must provide your indoor-grown plants enough blue light: you’re replicating that summer glow.

Green Light Spectrum

Green lights are another color on the light spectrum that your hemp plants are going to thrive under. However, unlike many other light spectrums we’ve mentioned, green lights are miles more versatile.

At the end of the day, it will be up to preference when green lights are used during the growth process, as growers can utilize them in various stages. Some growers choose green lights during the seedling stage of their plants to help support healthy root growth. Other farmers turn on green lights during the end of the vegetative state to provide the hemp with a last boost of nourishment before flowering begins. Still, there have been various accounts of successful yields with green lights during the hemp plant’s flowering stage. So, as we mentioned, the choice is yours!

Luckily, the green light spectrum can be found in other colors like reds and blues, too, so you don’t always have to have just green lights on your hemp. Instead, a nice mix of blue and green may be the best route for your healthy, potent plants.

Red and Far-Red Light Spectrum

As summer begins to come to an end and fall starts, hemp plants out under the care of Mother Nature will be exposed to more red light from the color spectrum. This is one of the most prominent signals that winter is coming, and it’s time to start flowering.

Growers should use red lights like these throughout the flowering stage of their hemp plants. Red lights help your plants get that extra energy they need to produce their full, CBD-filled flowers and even elongate their stems slightly more. Be careful, though! Too much red light can cause overgrowth for your plants, making them lose their excellent structure. Keep an eye out for your plants’ stems: if they start to grow too much during this stage, it’s likely the presence of your red lights. Tone them down a bit and see how your plants react from there. It’s all trial and error.

Perfecting Your Hemp Harvest

The best way to ensure a perfect hemp harvest is to pay close attention to your use of lights and color spectrums. As we’ve stressed, it is beneficial to provide your plants with a balance of myriad colors during different stages of their life. When you do this and help replicate the kind of exposure your hemp would get outdoors, the plant will surely flourish.


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