Story photos by Erik Biksa
The plants shown being harvested in this garden (courtesy of the Urban Grower) were cultivated in a controlled-environment agriculture (CEA) system that allowed the grower to exercise perfect control over every environmental parameter in the growroom. Daytime and nighttime temperatures are controlled independently and accurately via air-conditioning; excess humidity is removed from the air with industrial dehumidifiers; carbon-dioxide levels are supplemented with a gas-fired CO2 generator; and the air is kept clean and pure with large, activated-charcoal air scrubbers and fans. All of these appliances are connected to precision sensors and monitors that allow the grower to create (and modify) the perfect climate for producing a heavy and sticky harvest of high-quality cannabis.
The level of control in this type of growroom is excellent – but, much like a computer, it’s only as good as what you tell it to do. Most cannabis growers recognize that different strains have different preferences when it comes to the growing environment and nutrients. Experienced farmers recognize that at various times throughout the growth cycle, different strains can be manipulated in different ways to enhance the characteristics and traits desired.
Consider that in natural (i.e., outdoor) settings, cannabis plants receive differing intensities, qualities and durations of light. In addition, nutrient availability changes throughout the growing season. When growing indoors, however, growers have the ability to tightly control these and other growing parameters.
The Vegetative Stage
After the pre-veg phase, in which newly rooted clones or young seedlings are conditioned for more intensive growing conditions, the crop is ready to enter the vegetative-growth stage. Here, the goal is to develop a large root system and enough potential budding sites on each plant to fill the space allotted once the buds start flowering, while avoiding overfilling the space due to excessive plant heights and branching.
It takes research (and occasionally some trial and error) to accurately determine the best planting densities and times for vegetative growth to produce optimal results in any particular strain. It’s important to note that indica-dominant strains may grow very little once flowering is initiated, while sativa-dominant strains may triple or even quadruple in size before finishing. Thus, the length of time spent in the vegetative-growth stage needs to be adjusted accordingly for each plant.
In this particular garden, the plants experienced a five-week vegetative-growth period before the flowering stage was induced. During this time, each of these NYC Sour Diesel plants received plenty of space for both branch and root development. Just to highlight how important a large, healthy root system is for big yields of high-quality buds later on, it should be noted that the plants were grown in approximately 72 liters of peat-based soilless mix apiece.
The soilless mix is maintained with high levels of microbial life and bioactivity to help further stimulate the root systems and fill the large volume of growing medium provided to each plant. Beneficial inoculants are added with the nutrients to populate the growth medium and the root zones with fungi and bacteria such as Trichoderma, Pseudomonas, Azotobacter and mycorrhizae. The root systems are kept elevated off the cold floors, and the containers are placed on wheels so that each of the trashcans filled with soilless mix can be maneuvered easily through the growroom to help maximize light coverage for each plant.
Warm It Up
Slightly warmer temperatures help to increase the metabolic rate of activity in both the soil and plants. During vegetative growth, supplementing CO2 levels to approximately 1,000 ppm (parts per million) and maintaining even temperatures of 85ºF during the daytime and 80ºF at night proves to be optimal. The populations of beneficial microbes supplied via nutrient additives help to keep each plant’s root system healthy while functioning at the higher metabolic rates stimulated by the warmer vegetative-stage temperatures. By keeping the DIF (i.e., the temperature differential between day and night or light and dark) closer at this stage, the plants tend to produce tighter branching patterns, building an efficient framework for supporting large yields of dense, sticky buds.
In the early-veg stage, some growers prefer to keep their humidity levels slightly higher (for example, 65%) to give the plants an opportunity to set down some roots after transplanting. If the air is too dry, tender young plants will have to work hard to keep up with the water loss through their leaves, and this creates stresses that can reduce cropping potential and invite other problems. This is a great time to introduce predator insects like Phytoseiulus persimilis (which eat spider mites), because they tend to do better at higher humidity levels. Also, because the plants are smaller at this point, fewer predator insects can provide more effective coverage faster. The humidity levels are then gradually lowered as the veg stage progresses.
The first one to two weeks of flowering are often referred to as the “transitional growth” phase. During this time, nitrogen levels are decreased slightly while the levels of phosphorous and potassium are increased. Temperatures should be reduced to 80°F when the lights are on and 75°F when they’re off. Notice that the DIF is still narrow here; this helps to create tighter internodes at the onset of flowering, reducing the spaces between individual budding sites and producing more buds for harvest. CO2 levels are typically maintained at 1,000 to 1,200 ppm during this time, with a strain-dependent relative humidity of 40% to 55%.
At peak flowering (i.e., the middle of the flowering cycle), nutrient strengths and concentrations are at their highest, often averaging 1,500 ppm (approximately 2.0 EC) to stimulate and supply the intense structural development of the buds that occurs now. When using soil or soilless mixes, growers often follow a “feed, feed, water” regimen to help reduce the accumulation of nutrient residues that may occur in their medium. Growers who like to feed heavy will do a light flush of the containers or beds once every one to two weeks during flowering. A flush mix of humic acids and digestive enzymes proves to be ideal for this purpose, since it helps to reduce excess nutrients in the growth medium that can create nutrient imbalances or lockouts.
Humidity and temperature levels are maintained at their set points, with no changes until the late budding/ripening phase of the reproductive cycle. CO2 levels should be further elevated at peak flowering, and carbohydrates help to supply both the plants and beneficial soil life with an abundant source of energy when growth and development are occurring at a higher rate due to the growing environment provided.
For the ripening period – which typically consists of the last two to four weeks before harvest – medicinal growers shift gears with their environment and crop feedings to promote maximum bud swell and resin production as well as a smooth, clean taste in the harvested buds. Environmental manipulation can even bring out the best colorations in certain types of genetics (for example, beautiful purples and reds).
The Big Flush
For the final weeks before harvest, no base nutrients are applied. This helps to flush the plants and growing medium of any excess nutrients that may contribute to poor-tasting, hard-to-burn buds. A variety of rinsing agents can be used to help facilitate this process, although many growers (especially those reusing their medium, whether soil or soilless mix) prefer to flush with humic acids and digestive enzymes. In fact, growers who have doubled up on the rate of digestive enzymes mixed into the reservoir for flushing report marked improvements in both the quality of their crop and the suitability of their growing medium for reuse.
When significantly increasing the DIF between daytime and nighttime temperatures, growers should pay close attention to any rise in humidity levels during the dark cycle. Dehumidifiers help to keep the relative humidity (RH) from rising above 55% when the lights are off, which is necessary because excess humidity encourages bud rot and other plant diseases in the dense, heavy clusters of ripening cannabis.
It’s important that CO2 levels are lowered to ambient levels during the ripening phase (for example, 450 to 650 ppm). If CO2 levels remain higher at this stage, the buds may get bigger, but they’ll lack the density and intense flavors and colors that growers typically desire. This is because carbon dioxide inhibits the plant’s production of ethylene, a naturally occurring hormone that assists in the ripening process.
Light intensity can also be reduced at this time, since growers are more concerned with dissipating their plants’ chlorophyll content rather than building it up to achieve better-quality medicine.
Only after the grower is sure that the plants and growing medium have been adequately flushed of excess nutrients does the decision of when to harvest come into play. Well-flushed plants will usually show yellowing in the older fan leaves, signifying that excess nutrients have been transferred and used up by the ripening colas. With a magnifying glass or handheld microscope, the grower can inspect the swelling resin glands for signs of peak maturity.
A higher percentage of clear-looking glands indicates that the resins have not yet reached their full potency. This is desirable for some patients, since slightly less mature resin glands often have a more “heady” effect (as opposed to either a sedative effect or body stone) because the ratios of THC to CBD (cannabidiol) and CBN (cannabinol) are wider.
When the resin glands have gone from clear to milky white and opaque, the resin is at peak maturity. For most patients, this proves to be the ideal time to harvest, since there’s now a good balance between the THC and CBD/CBN levels, providing a more equal head-to-body effect. On the other hand, those patients looking for a body stone may want to wait until some of the resin glands have turned from milky white to amber: At this point, some of the THC is beginning to degrade and convert back into precursors like CBD and CBN. Growers who wait longer during the ripening phase may have slightly heavier harvests, but they are also much more likely to get a sleepier effect from their medicine.
Finally, some growers have noticed a higher rate of resin production when the plants are kept in total darkness for 24 to 48 hours prior to harvest. Some studies suggest that resin production in the cannabis plant peaks just before the sun comes up (or the lights are turned on), so the extra darkness may promote a final burst of resin secretion.
There are many different strains of cannabis that appear highly suited for treating various ailments, with each strain possessing its own unique resin profile. Growers can use carefully controlled environments and nutrient programs to bring out the best in a chosen strain and, in some instances, even enhance what it has to offer – resulting in cannabis that is potentially more effective for each patient’s unique needs.