Marijuana plants rely on photosynthesis to grow. For that to work, they would need the leaves to absorb carbon dioxide from the air and the roots to keep assimilating water and nutrients from the substrate. They also need chlorophylls to work hard on collecting the one key ingredient that makes the whole process run like a well-oiled machine is light, be it from the sun or grow lights. Before any of this, if you need any extra information on the types of light to use when growing indoors, check out Choosing Your Lights with Kyle Kushman and learn from a master cannabis cultivator.
Light and Photosynthesis
You know what is needed, but now it’s time to discover the mechanisms involved. Once you understand the whole process, especially the role of light, it would be easier for you to help them thrive.
I. Converting Light to Energy
One way to define photosynthesis is that it is the process of converting light into energy. Marijuana plants, along with practically all plant species, do this. Tasked to collect light are green photosynthetic pigments in the leaves – chlorophylls. There is nothing much you can do here except to make sure that the plants receive ample sunshine. Indoors, that entails using artificial lighting.
As far as grow lights go, the plants can only grow to their full potential if they are made specifically for horticulture.
In nature, sunlight changes with the seasons. So indoors, you are not merely concerned with providing “light” but also mimicking the conditions in line with the seasonal changes. You would need two types of lamps to accomplish that.
During spring and summer, when the plants are in the vegetative stage, the blue color spectrum from sunshine is more prominent. In turn, the plants have evolved to use this wavelength to grow stems and leaves, gaining mass over the coming weeks and months.
In the fall season, the sunlight tilts toward the red spectrum due to the sun’s lower position in the sky. By this time, the evenings are longer than they were in spring and summer. The extended period of darkness signals to the plants that it is time to prepare for winter, and they do that by switching to the flowering stage. You would see them stretching vigorously for a couple weeks and then start budding.
Both CO2 and water are needed for photosynthesis, and the plants can get them from the air and the ground. As for indoors, you can ensure that the plants have access to them by providing fresh air in the grow room and using an appropriate medium.
Throughout their life cycle, the plants create carbohydrates (sugars) for nourishment as they grow. These sugars also mix together to form cellulose, which can comprise up to 80% of their structure.
How Exactly Do Plants Make Sugars?
During light absorption, two chemical compounds come into play. One is nicotinamide-adenine-dinucleotide-phosphate (NADPH2), which synthesizes carbohydrates. It will also require adenosine-triphosphate (ATP) to aid in the process. Throw in CO2 and water, and they all combine to create sugars and oxygen.
This process keeps going on during daytime (or light on hours), in which plants use sugars and oxygen to create more sugars while releasing excess oxygen into the air.
How Do You Enhance Sugar Production with CO2?
Increasing CO2, being one of the essential ingredients, should result in more carbohydrates created. If you can do that, then that is one way of boosting plant growth. A well-ventilated grow room usually would have around 400 ppm of CO2. In creating the perfect environment, one of the things you do is raise that to 1200-1500 ppm and, at the same time, maintain 85-95°F (30-35°C). That should help maximize the production of buds.
Do Leaves Matter?
Most definitely. For marijuana plants to thrive, they would need full-grown leaves to manufacture sugars. Did you know that there is a correlation between sugars created and the final yields? Up to 2/3 of sugars eventually end up in the buds. And so, how well the sugars travel and reach the buds also matter.
Leaving all the leaves alone throughout the lifecycle is fine. Your plants will have plenty of sugars to fuel the growth of buds. You can, of course, optimize or boost the production by trimming young leaves and side shoots in the lower parts of plants. The idea here is to focus the distribution of sugars in the upper canopy where there is adequate light distribution.
What About Darkness, Does It Matter in Photosynthesis?
Up until this point, it has all been about light, CO2, and water. It makes sense because that is when photosynthesis occurs. And so, what role does the dark period play? Actually, this does have at least two super essential functions – protein and breather from nutrient uptake.
During the day, the plants make sugars. In the evening or dark period, they create proteins, which process leftover oxygen created earlier. Proteins help in the process called “plant breathing,” in which the plants release oxygen, CO2, and water vapor.
During the lights on hours, the plants will need plenty of water, and they get that from the substrate. In doing so, the roots also absorb nutrients, together with water molecules. Now, the plants have no way of separating water from nutrients. It cannot selectively absorb only water when there are more than enough nutrients in their system.
A dark period, in this case, serves as a breather or a break. It allows the plants to utilize the water and nutrients already collected without adding more. Quite simply, this form of self-regulation lets them avoid excessive uptake.
III. Sugar Distribution
Sugar is much needed by practically all parts of the plants. In some ways, you could say that there is even a competition for this valuable resource. Now, the way it is distributed is through a principle called “sink strength.” You can think of it like this. Each part of the plant has a sink that sugar can flow into. Naturally, the more sizable plant parts would have more substantial sinks, and so they receive more sugar than others. For marijuana plants, the primary bud site’s sink strength is usually three times stronger than new growths.
Regardless of how much sugar was created during photosynthesis, the buds (especially when nearing maturity) will always receive three times more than other plant parts. And that makes sense because its intention is to propagate. So the reproductive organs should be well-developed, thus ensuring the survival of their species.
When the environmental conditions are suitable, the plants receive plenty of light and CO2. The roots would gather water and nutrients. All these combined let the mature leaves manufacture more sugars than they need. The excess is transported to other plant parts in need – the young foliage and more specifically the buds.
Can You Interfere with Sugar Distribution to Boost Growth?
Of course, you can. Although the plants allocate sugars as nature intended, you can still influence the concentration that reaches the buds. Trimming, for example, is one way to reallocate this valuable commodity to grow larger, denser buds.
As was emphasized, the plants need leaves to produce carbohydrates. So, generally speaking, you leave them alone. Moreover, you should do everything you can to keep them healthy.
By carefully inspecting each plant, though, you would notice that the young foliage beneath the main canopy may not recieve much light. In other words, they are likely not producing enough sugars. Or worse, they may actually be consuming more than they could make. In this case, you can safely trim these young leaves.
On the upper canopy, the fan leaves are busy, making most of the sugars for the entire plant. And why not? They have access to light and CO2. As for the ones at the bottom, they usually would fall off on their own. Trimming is only a way for you to help them do that quickly and save valuable resources for essential parts.
It Is All About Optimizing Photosynthesis
As you have read, the plants already have the mechanism for photosynthesis. When thinking about boosting growth, producing more substantial buds, and higher THC production, you think about how to make that process efficient.
For starters, you need to ensure that they receive not only enough light but also the correct color spectrum depending on their growth stage. Moreover, they would also need CO2, and keeping the grow room well-ventilated assures that. Meanwhile, beneath the substrate, they need access to water and nutrients.
As the plants work their magic, producing sustenance for themselves, you can also intervene to optimize the growth. By removing non-essential parts such as young leaves at the bottom, which do not contribute to making sugars, the buds will receive more. Consequently, they would have the resource that allows them to grow large, dense, aromatic, and highly potent.
As much as you want to think only about the grow lights, it is but merely one component among others that is needed for photosynthesis. Nonetheless, it does play a significant role.
For more information on cannabis plant proccesses and utilising light correctly, head over to the Homegrown Forum and see what advice you can get from fellow growers!