The goal when growing basically any plant is to obtain optimal growth and the best possible results come harvest. Cannabis is no exception. Any way we look at it, growing a cannabis plant to its true genetic potential is the key to a successful grow, and a successful grow is usually determined by the amount of end product harvested. In this case, that amount is measured by weight. For those growing for commercial gain, more weight equals more money since cannabis is sold by weight.
For someone growing for just personal medicinal or recreational use, more weight per plant means more end product that will last longer between grow cycles. Either way, the goal is to achieve as much end-product weight as possible and the best way to reach this goal is by growing the biggest buds the plant can possibly put out.
In this piece we will explore some of the most important parts of the growing cycle and how perfecting them can lead to great big buds and help a grower achieve a maximum yield.
Cannabis is what we refer to as a photoperiod sensitive plant, meaning the plant’s growth cycles are largely controlled by the amount of sun or, more specifically, the amount of darkness it receives at a given point. Cannabis is classified as a “short day” plant. This means it requires at least 12 hours of uninterrupted darkness before beginning its flowering cycle. The exceptions to this rule are the ruderalis varieties that do not require a change in darkness hours to initiate flower. They simply begin flowering when they reach a desired point of maturity, which is why they are referred to as “autoflowering” cultivars.
Outdoors the change in darkness hours occurs after the beginning of the summer solstice, which occurs around June 20-22 each year. At this point the nighttime hours continue to increase until reaching the winter solstice in late December, when the process is reversed. Outdoor cannabis plants tend to start flowering around mid to late August when the darkness hours reach the desired amount, depending on the variety.
Indoors, however, growers have ability to manipulate the lighting schedule and increase or decrease the dark period at will. This allows us to force or trigger a plant into flowering whenever we desire. When plants are in the vegetative stage, the goal is to keep them there for as long as needed and to keep them from going into flowering mode. This is achieved by not allowing them to have 12 hours of darkness per day.
The common way of going about this is setting the lights on a timer so they are on for 18 hours and off for six hours per day; this approach sort of mimics spring and early summer conditions outdoors. When the plants are ready to go into the flowering stage, the lights are typically set to a 12-hours on and 12-hours off schedule. Flower development usually starts to visibly occur within two weeks after the switch. Again, the most typical approach for indoor growing is keeping the plants on a vegetative light cycle for about four weeks and then in the flowering cycle for around eight weeks.
This can be subject to change depending on the size of the room and the variety being grown. For instance, some varieties need a bit of a longer flowering cycle before reaching maturity and some growers with taller ceilings may prefer running the vegetative cycle longer because larger plants usually yield a larger harvest.
Good Air Circulation
This is easily one the most important things to consider when growing indoors, especially in a smaller room or grow tent. When a plant is performing photosynthesis, it takes in carbon dioxide (CO2) while releasing oxygen (O2) and water vapor into the surrounding air. This all takes place through small, pore like structures called stomata that are found primarily on the bottom of the leaves. As the O2 and water vapor are released, vertical pressure is created which carries more water and nutrients up through the roots.
Without proper air circulation through the plants’ canopy, the water vapor has no way to evacuate the space between the leaves and moisture can accumulate. The longer the moisture accumulates, the higher the chances become of mold or fungal growth developing. Both can be detrimental to plant growth and should never be allowed to proliferate. Good airflow through the canopy forces the moisture away from leaves, keeping them dry and drastically reducing the possibility of mold or fungal growth from occurring. It also creates a steady flow of new CO2 reaching the stomata, ensuring regular photosynthesis is uninterrupted.
Another valuable result of proper air circulation is it can help keep the surface of the leaves cool which can be important under the heat of today’s high wattage grow lights.
Light waves that plants can use are quantified by measuring the amount of photosynthetically active radiation, commonly referred to as a PAR measurement, which measures the wavelengths of light in nanometers and helps determine which color spectrums of light are most effective for growing with artificial lighting. The PAR spectrum for plants is basically between 400 and 700 nanometers with measurements below 400 bringing in ultraviolet wavelengths and above 700 bringing in the infrared spectrum. The closer the measurement is to 400 nanometers, the more the color blue is in the spectrum and when the measurement is nearing 700 nanometers the spectrum is more dominated by the red light spectrum. In the middle of the PAR scale is the green spectrum which is still being debated and studied to determine whether plants can use this spectrum for photosynthesis.
The key to determining which light intensity is best for a growroom or tent is by using a PAR meter and not getting too carried away with lighting that is more than what is needed, which is just a waste of energy at the end of the day. During the vegetative stage plants grow best under a light that is more in the blue spectrum of PAR, between 400-500 nanometers.
Light choices that are best suitable for this are T5, T8, or T12 fluorescents or 400-600W metal halide (MH) lamps. These styles will deliver enough PAR to maintain good plant growth and they also stay relatively cool compared to other lighting choices. In the flowering cycle, a light that is closer to the 600-700 nanometer measurement of PAR is ideal as plants flower better when receiving light in the red spectrum. The most common type of light used in this stage are high pressure sodium (HPS) lamps. These give flowering rooms that classic orangish glow. In most situations a 400-600W HPS lamp will provide enough PAR to accommodate heavy flowering but these do run much warmer than the other lights I mentioned, so good air flow or perhaps other methods of cooling the grow area may be needed.
In larger rooms it isn’t uncommon to see growers using 1,000W HPS lamps but it’s important to remember that with that much light intensity it may be necessary to supplement extra CO2 to keep up with the increased rate of photosynthesis.
While creating the ideal environment for indoor cannabis cultivation is key, it is also important to ensure the plants are receiving proper nutrition. Plants require 16 essential nutrients in order to complete the growth cycle in a healthy and successful way. Throughout the different stages of growth these nutrients are needed in varying ratios. I won’t go in depth on what each nutrient does and the amounts needed at specific times because that would be a whole separate article on its own. Instead, let’s focus on the three most notable nutrients: nitrogen, phosphorus, and potassium, often referred to as the NPK. These are the three numbers that are typically prominent on a fertilizer label and separated by dashes (i.e. 10-10-10). These three elemental nutrients are of highest importance to plant growth and they are referred to as “macro nutrients.”
When plants are in the vegetative growth stage, they require more nitrogen than any other nutrient. Nitrogen is responsible for the formation of the amino acids and proteins that are present in every part of the plant. A higher nitrogen fertility program will encourage robust vegetative growth giving the plant the ability to create and store more energy that it will use later in the flowering cycle. Increased vegetative growth leads to more leaf production and in turn more leaf surface area.
The more surface area a plant has, the more photosynthesis it can perform leading to a higher level of carbohydrate production that results in more energy for growth.
In the flowering cycle a fertilizer with higher levels of phosphorus, compared to nitrogen, is desired. This stage requires more phosphorus, along with potassium, to maintain strong flower bud development. Limiting the nitrogen in this stage will slow down vegetative growth and direct more nutrients and stored energy directly to the developing flowers. The more energy stored during the vegetative cycle the better, because it will be used to help the flower buds grow to their highest potential.
Many growers will also incorporate a fertilizer product that has a higher ratio of potassium compared to nitrogen and phosphorus during the last two to three weeks before harvest. Potassium has been known to increase the size and density of flowers and fruits in most plants and can help add some much-desired bulk to the buds prior to harvest. Creating a structured fertility program can be a bit confusing for the less experienced grower, which is why I think it’s important to remember there are hundreds of companies that sell products that are specifically designed for each stage of growth. This helps take the guess work out of fertilizing and is a great way to start.
The overall goal when pruning or training a cannabis plant is to allow as much light as possible to reach as much of the plant as possible. Pruning and training are also a matter of the right approach at the right time. In vegetative stage, light pruning is important to maintain proper air flow through the plant canopy, but we also want to keep enough leaves to maintain a high rate of photosynthesis.
Basically, the best pruning method for this stage is removing any lower leaves or stems that are obviously not receiving any significant amount of light. These portions are generally not doing much to increase plant growth and the nutrients and energy used to keep these areas growing will be better used in other parts of the plant. In this stage a grower can also do some light training. By using a netted plant trellis placed horizontally just above the growing tips of the plants we can train the growing stems to grow through the grids in the trellis allowing them to be somewhat separated from one another; this helps more light reach more leaf surfaces.
Read also: How to Master Cannabis Mainlining
For the flowering cycle a more deliberate method of pruning can be utilized. Removing many leaves from six to eight inches below the major flower bud sites will eliminate those that don’t receive much light as it is and encourage more nutrients and energy to be used directly on the larger buds, increasing their overall growth. It is also helpful to completely remove any smaller lateral stems with small flower buds that typically don’t amount to much. Those portions of the plant are a relative waste of nutrients and energy, and the resources will be better used on the larger flower buds higher up on the plant.
Determining when the buds are at peak ripeness and when the right time to harvest has arrived is just as important as any other stage in a growth cycle. There is no point in doing every other step with due diligence only to end up harvesting at the wrong time and ending up with a less-than-optimal end product. There are two main methods to determining when the buds are ready for harvest and both can be used simultaneously.
The first method is by closely observing the flower’s pistils. The pistils are the fine hair-like structures that protrude from the flower itself. In nature these are used to catch the pollen from the male flower to allow the plant to reproduce. Since most cannabis is grown for the female flowers, the pistils can be used to determine ripeness. The pistil hairs will typically start off as white. At this stage there is very little THC being produced. As the flowers mature the pistils will begin to change to a more brownish-orange hue, signifying THC production is on the rise. If a more clear-headed high is desired, the buds should be harvested when around 40-60 per cent of the pistils have changed colors. When upwards of 70-90 per cent have changed, the THC will begin to convert to cannabinol (CBN) and the end product will have more of a sedative like effect. It all depends on what kind of effect is desired.
The second method for determining when to harvest is by paying attention to the trichomes on the leaves surrounding the flowers. The trichomes are the tiny mushroom-shaped glandular structures that give cannabis buds their well-known crystal-like appearance. They also help us determine the best time to harvest. For this method, it is advised to use some sort of magnifying glass — the ones jewelers use work perfectly.
Much like the pistils, the trichomes also go through a transformation. They first start off clear as glass, when THC production is relatively low. As the flower buds mature the trichomes will start to change to a more cloudy or opaque look. This is when THC production is ramping up. Once 80-90 per cent of the trichomes appear this way, THC production is peaking and should be harvested for the more clear-headed high.
Once the THC begins to convert to CBN, the trichomes start to change to an amber color. The buds will be best off harvested before five to 10 per cent of the trichomes turn amber unless the more sedative effect is desired. It is important to note that certain strains will have different color pistils and trichomes, but the underlying process is the same. Take time to study the variety being grown to completely understand what to look for.
Of course, there is more involved when it comes to achieving a successful grow cycle than simply what has been addressed in this piece. But by paying close attention to these aspects of the process a grower will be well on their way to growing some big, fat, stinky buds and reaching that ever-so-desired maximum yield.