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Taking a Look at the Cannabis Light Cycle

With marijuana now becoming increasingly legal across the nation, more people are thinking of growing their own cannabis gardens at home. It’s not an overly difficult endeavor. After all, marijuana is a hardy plant with strains growing wild around the globe. Some spring up and thrive in even the harshest growing conditions.

Still, to get the highest possible yields and quality out of your cannabis seeds, you need to know what it needs to flourish. Nutrients, water, and air are all vital resources for marijuana to draw from, but light is one of the most crucial elements to consider. Fully understanding the cannabis light cycle and how it affects the plants will make a significant difference in your crop.

Cannabis Craves Light

Like all plants, marijuana requires light to complete the process of photosynthesis. Without light, cannabis plants can’t transform nutrients into the energy they need to grow, produce buds, and generate THC and CBD. Light also helps encourage your plants to draw in carbon dioxide for food and give off oxygen.

As a photoperiodic plant, marijuana also relies on light for another critical purpose. It looks to the light to tell it when to grow taller and branch out and when to redirect its energy to flowering. Of course, light, in general, isn’t the only factor here. These plants need specific types and amounts of illumination to complete their lifecycles. For the purposes of this article, we will discuss light’s impact on photoperiodic plants only. There are of course autoflowering strains available that can flower in almost any kind of light schedule – but we will cover this in another article.

Digging Deeper into Cannabis’ Dependence on Light

In nature, cannabis plants enter various stages of their lifecycles based on light. After germination, the tiny seedlings peek out from the soil in search of sunlight. Ideally, this should take place in early spring.


A Brief Science Lesson

Specific growing seasons vary across North America as well as by year, but in Ontario, they usually start in late May and come to a close around the end of October. It’s best to plant your outdoor marijuana as quickly as possible after the last frost of the season, so it has plenty of time to grow and mature before the first frost of fall.

Each year as spring evolves in our area, Earth’s Northern Hemisphere tilts toward the sun. Temperatures begin to climb, and we emerge from our cold, dark winter funk. Along the way, days grow longer, and sunlight from the blue area of the spectrum floods our region with its long-awaited presence. As we venture into summer, we enjoy about 18 hours of glorious warmth and sunlight each day followed by an estimated six hours of slightly cooler darkness.

Eventually, we begin to tilt away from the sun again. This signals the beginning of autumn. Daylight hours dwindle to about 12 per day, and the darkness is equally divided. Temperatures gradually drop, and light from the red and orange field of the spectrum replaces its blue predecessor. All the while, growers in the Southern Hemisphere experience quite the opposite turn of events.


Back to Light’s Role in Cannabis Cultivation

After it’s planted in early spring, cannabis seeks out those ample hours of blue light. This tells the seedlings it’s time to grow and branch out as they forge through their vegetative states. When blue light begins to fade to red and orange and the number of daylight hours decreases, those tall, bushy plants nearing maturity realize it’s time to enter their flowering phase. This is the time when buds develop, expand, and amass generous doses of THC and CBD.

How Does All This Happen?

Marijuana plants crave plenty of blue light. It gives them the energy they need to transform nutrients into usable food and other resources. At the same time, it prompts them to continue drawing in water and nutrients from the soil, eliminating waste, and performing other vital processes. This blue light during the long days of summer helps prepare the plants for the next stage in their progress.

Despite the need for blue light, cannabis plants also have red light receptors in their leaves. Known as phytochrome red and far-red, those receptors remain on a continual mission to seek out light from the red end of the spectrum. It’s there even when blue light is dominant, just in smaller amounts.

Phytochrome red and far-red soak up red light throughout the plants’ lifecycles. Far-red encourages the plants to remain in their vegetative states whereas red causes them to enter the flowering stage. Far-red converts to red during those nighttime periods without light. As long as the nights are short, far-red prevails. When the nights grow longer, though, red becomes the dominant phytochrome, and flowering begins.

Light Cycles for Indoor Marijuana Plants

Traditionally, indoor marijuana plants expect the same light cycle as their outdoor brothers and sisters. They don’t realize they’re indoor plants. All they know is what their ingrained DNA and numerous specialized cells tell them to do. That’s to relish in long hours of blue light, take in as much red light as possible, and watch for cues from Mother Nature to tell them when fall is coming and it’s time to flower.

Giving Indoor Marijuana the Light It Needs

Since indoor cannabis plants don’t have sunlight at their disposal, it’s up to you to give them the light they need. You have to regulate the type and intensity of light they receive as well as the amount of time they’re exposed to darkness with each 24-hour cycle.

Many growers choose LED grow lights because of their relatively low operating costs. LEDs offer a broader spectrum of light than some other options, too. This means they’re appropriate for all growth stages.

Metal halide grow lamps give off broad-spectrum light as well, so you can use them throughout the growing process. Experts recommend grow lamps offering at least 12 percent blue light output during the vegetative phase. T5 fluorescent lights are also great for this stage.

If you want to give your cannabis plants a more natural, well-rounded experience, though, your best bet would be to change out your grow lamps during the plants’ lifecycles. After giving them a growing season of blue light for vegetation, switch to lamps that put out red and orange light. High-pressure sodium lamps work best for the flowering stage.

Timing Is Everything

In the event you’re in no hurry, and you want to see your cannabis plants through their natural lifecycle, it’s important to start out with low-intensity illumination and lamps that produce blue light. After a brief germination period, you’ll need to give your plants 18 hours of light followed by six hours of darkness just like they’d receive outside.

Marijuana strains vary in the amount of time they take to mature and begin flowering. Some take as little as a couple months whereas others may take seven months or more. This is where you come in. When you grow your cannabis indoors, it’ll remain in the vegetative phase as long as it gets 18 hours of light each day.

Most indoor growers allow their plants about five to eight weeks for vegetation. This gives them plenty of time to grow strong and bushy with numerous nodes where buds will ultimately appear. Then, you’ll need to switch over to red and orange light and reduce the amount of lighting to 12 hours per day. Doing so mimics the natural transition of summer to fall.


Manipulating the System

You probably already know one of the main advantages of growing indoors is being able to speed up the process and bring on the flowering phase more quickly than nature typically allows. Though plants will remain in the vegetative state as long as you give them 18 hours of light each day, it’s possible to trick them into transitioning to the flowering phase after only three or four weeks of growth.

Allowing the plants to grow a bit longer than three weeks before prompting them to flower is advised. This way, they’ll be bigger, stronger, and able to produce and support more buds. Their buds will also be more potent in most cases when you wait a little while before swapping to a 12-hour light cycle.

Plants will enter the flowering phase once you switch their light cycles to 12 hours per day, and most strains take about eight to 12 weeks to complete the bud-production process. Keep in mind, consistency is everything. Once you initiate the flowering phase, be vigilant about turning off the lights after 12 hours each day. You may want to use a timer. After all, at that point, it’s about the darkness as much as the light.

Human Intervention for Outdoor Marijuana Plants

Several growers prefer a bit of a hybrid growing process as opposed to growing their marijuana strictly outside or inside. It’s best to plant your cannabis seeds in pots for this approach. If you want to try this method, you have a few options to choose from.

For one, you could allow your marijuana to remain outside around the clock during the first few weeks of its vegetative state. Then, simply start bringing the potted pot plants inside and placing them in a dark room after 12 hours of sunlight on your patio in California or Hawaii

You could also set up a portable greenhouse or build a rudimentary shed for your plants and cover them with dark material or a tarp a few hours before the sun goes down. This is a great approach for growers in Nebraska or Wyoming who want to keep their activities more private. Either way, the most important part of the process is taking away their light about six hours before sunset.

Alternatively, you could plant your marijuana in pots and give them constant light for a few weeks of the vegetative state. Allow them to enjoy natural sunshine and fresh air during the day and bring them indoors to artificial light once the sun starts to set. From there, switch to a 12-12 light cycle to kick-start and sustain the flowering process.

Can I Grow Marijuana Indoors Near a Window?

The short answer here is yes. Technically, it’s possible to grow marijuana indoors near a window without using grow lights. Of course, several problems enter the mix with this technique. First off, you’d need a window with exposure to sunlight for at least 18 hours a day. Otherwise, you’d have to move your plants from one window to the next as the sun proceeded across the sky.

Secondly, even if you were able to give your cannabis plants 18 hours of sunlight via windows, you wouldn’t be able to grow many plants using this method. Remember, all marijuana plants need equal amounts of sunshine. Unless you have an extremely large, wide window, only one or two plants would get the amount of light they need. Those not immediately in front of the window would essentially starve.

Lastly, modern windows just aren’t designed for feeding sunlight to houseplants. They’re made to filter out certain UV rays, increase energy efficiency, and prevent furniture fading. This means your plants may not thrive if you simply place them in your kitchen window.

UV rays come in three distinct forms: UV-A, B, and C. Though our atmosphere blocks UV-C from reaching Earth, plants depend on A and B for survival. These two crucial types of UV rays enhance the potency of the buds as well as their taste and aroma.

All Things Considered

Marijuana, like all plants, relies on light to make food. As a photoperiodic plant, it also uses light as a cue to switch from one phase of its life to the next. Cannabis’ bud production and potency likewise depend on illumination.

Cannabis naturally looks for an ongoing cycle of 18 hours of light followed by six hours of darkness during its vegetative phase. Once this evolves into a regular sequence of 12 hours of light and 12 of darkness, the flowering phase comes into play.

Mother Nature provides these elements and changes automatically. For indoor plants, though, you’re responsible for them. Several options are available for both grow lighting and altering the light cycle to affect growing and flowering times. Regardless of the method you choose, consistency and providing the right types and amounts of light are the keys to success when growing your American wholesale seeds.

Our team at Weed Seeds USA is dedicated to helping make your seed purchase as seamless as possible. We can offer our Oklahoma clients the chance to pick up their seeds directly, but we also ship to all the other 49 states.


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