Most cannabis information available today is based on observations made by underground growers during repeated production cycles over the course of the past several decades. Indeed, prohibition has stifled cannabis research for most of the 20th century. In the near future, however, there will be many legitimate cultivation studies as legalization and legitimacy often come with the ability to scientifically research and examine all aspects of cannabis cultivation practices.

Until those studies are published and shared across academic and cultivation channels, cannabis cultivators are left with dozens of questions, including: Are there other, more productive growing methodologies than what I am currently using? Are there cultivation methods that enhance production of certain cannabinoids or terpenes? Which input has the biggest positive impact on yields and cannabinoid production?

Given the many variables under a cultivator’s influence, it’s good to question your practices today so that you remain ahead of the technology curve tomorrow. Here are six areas in which more information will spur further questions and better solutions.

1. Lighting:

Do we know exactly what light level and spectrum each cultivar prefers in each stage of production?

Is it a fixed spectrum, such as a blue-dominant spectrum in vegetative growth and a red-dominant spectrum in flowering stages, as is commonly believed and accepted as fact by some? Or is it possible the plant prefers a roving spectrum throughout a daylight period so that all spectrums are available throughout the day? Or is it best to mimic nature and utilize blue and red spectrums as many currently do? Conversely, is there a preferred targeted application that yields superior results? Is there a perfect spectrum for every stage of growth? These are the types of questions academic studies and white papers can and should answer.

2. Precise nutrient application and utilization:

I have witnessed clones taken from the same mother plants inexplicably outperform all others clones around it under similar environmental conditions and lighting, and in the same growing media and amendments. The only hypothesis I could drum up was that the plant received exactly what it wanted exactly when it wanted it, whatever “it” is.

Today, reports on nutrient applications are starting to hit the mainstream cannabis market (including in Cannabis Business Times’ “Nutrient Matters” series by researchers at North Carolina State University (NCSU)). These first studies are looking at the low-hanging fruit of cannabis nutrition, namely: What are the specific nutritional requirements of a cannabis plant in each growth stage? Many growers might intuitively know this, but it does not take away from the importance of such studies leading us to a deeper understanding of how this plant works.

Indeed, projects like the NCSU research could help growers determine if we sometimes apply fertilizers or amendments that are not utilized by the plant during specific stages. If it can be shown that cannabis plants only use/absorb/feed on certain elements at certain life stages and completely ignore anything that is not needed, growers can develop more efficient and precise nutrient application systems and methods, which is both environmentally and financially responsible. Deeper analysis into nutrient needs of cannabis plants also might reveal systems, nutrient formulations or amendments that accentuate or accelerate the production of biomass or desirable compounds.

3. pH fluctuation:

Traditionally, cannabis growers prefer a pH range of 5.8 to 6.8. Many choose 6.2 to 6.4, as within this range, they are likely to get most, if not all, of the desired nitrogen, potassium and phosphorus (NPK) minerals, as well as many other essential elements required for healthy plant growth. By raising or lowering the pH of a nutrient solution, it raises or lowers the availability of the required elements.

Is a plant receiving the desired amounts of elements at proper levels when employing this method? Or would it be best to fluctuate the pH? Put differently, would a slight variation in pH from one watering cycle to another improve health, growth and cannabinoid production? If you had a watering cycle that watered plants two to four times a day depending on methods and media, the first application of the day could have a pH of 5.8. The second application could be 6.2, the third could be 6.4 and the fourth could be set at 6.8. Would fluctuating the pH during watering ensure that all NPK elements are fully available throughout the watering cycle? Or would that be ineffective?

4. Temperature fluctuation:

Traditionally, indoor cannabis is produced in a very controlled environment where high and low temperatures are set and closely monitored. Outdoor plants, for their part, are subject to the whims of nature, resulting in wide-ranging daily and seasonal swings in environmental conditions, especially temperature. Outdoor cannabis plants typically flower in late fall, when temperatures are cooler. (Daily light interval (DLI) determines when a cannabis plant will flower, not temperature, but that is not the focus here.)

But what temperature range is best? Should you maintain constant set point temperatures? Or maybe allow for outside temperature fluctuation influences to dictate temperatures to some degree? Not too extreme, but perhaps you should set cooler temperatures in flowering stages and night cycles to mimic daily and seasonal temperature shifts.

Which temperatures are best for cannabinoid production and terpene preservation while maintaining proper humidity and vapor pressure deficit parameters? Cooler temperatures lend themselves to terpene preservation as terpenes evaporate at higher temperatures, yet most cannabis cultivars’ yields suffer if cultivated in cooler environments. There is an obvious balance between healthy and vigorous plants that yield well, produced in warm environments, and plants produced in cold/cooler environments with a primarily focus on terpene production and/or terpene preservation. What temperature is best for compound production and preservation? And what are the parameters?

5. Ethylene Gas:

Besides the factors listed above, there are many influences to investigate that have been utilized for decades by modern agriculture in a multitude of applications. For instance, ethylene gas is utilized to accelerate the maturation of fruits and flowers in some cases. I have seen a grower who used an ethylene gas buildup during the last days of flowering to cause a majority of a plant’s large fan leaves to dry up and fall off, without compromising the product’s quality. Would it be possible to mature cannabis early without compromise of yield, desirable compounds, or quality at scale by elevating ethylene levels?

6. UVB light spectrum levels for THC production:

Millions of dollars already have been spent investigating this one influence. Yet, even when compiled, the resulting studies and research are conflicting. Most published papers indicate there is a significant benefit to using UVB lighting to increase THC production, while investigations by others indicate very little impact.

Other questions remain: How much UVB light spectrum does a cannabis plant prefer? How much is too much? Can UVB have a positive influence on yield? Does UVB aid in control of contaminants such as powdery mildew?

But Wait, There’s More

Many other areas of cannabis production need further investigation. The cannabis plant is responsive to many influences, such as organic natural enzymes like seaweed and other organic inputs.

Plant hormones are another potential production influence that merits further research. Gibberellins are a group of plant hormones that stimulate stem elongation, germination and flowering. Auxin is another plant hormone that is produced in the stem tip and promotes cell elongation and inhibits growth of lateral buds.

All of this is to point out that we don’t know what we don’t know, and I believe a lot of facts about cannabis cultivation and commercial production have yet to be truly established. So, avoid sticking to your guns unless you have research as ammo.

Kenneth Morrow is an author, consultant and owner of Trichome Technologies. Facebook: TrichomeTechnologies Instagram: Trichome Technologies k.trichometechnologies@gmail.com

Air purification is critical to create an ideal environment for an indoor grow. Your facility’s air quality directly affects the environmental systems, integrated pest management and human comfort. With proper design and preventative maintenance, better crop quality can be ensured through reduced pest pressure and best care for environmental control systems. Here are eight tips for proper and efficient air purification.

1. Facilitate proper air movement throughout the growing environment to assist in maintaining optimal temperature and humidity. This is achieved through horizontal air flow and air exchanges. Microclimates within in the crop can create ideal environments for diseases and other pests, so to reduce pest pressure, create air flow that minimizes humidity and heat pockets. Air exchanges move air through the entire room and create an opportunity to purify air. At Pruf Cultivar, a vertically integrated company based in Portland, Ore., we complete 30 air exchanges per hour.

2. Create a multilayer system of filtration. Implement different technologies to reduce the presence of pathogens.

Prefilters: Use passive, lower-cost filters to trap larger particles, which will permit the finer and more expensive filters to work more efficiently and longer. A pleated filter creates a larger surface area, increasing filtration with higher air flow.

Carbon/Charcoal filters: These filters trap passing organic matter and reduce odor.

Excitation technology: This technology uses an electrical field to increase particle collision (excitation), which makes smaller particles stick together to create larger particles, enabling the HVAC filters to remove the resulting, larger particles permanently.

Ionization technology: These systems contain an electrical field and two electrically charged plates—one negatively charged, and one positively charged. As a particle passes through the electrical field, it is ionized and attracted to one of the two plates, removing it from the air stream.

Ultraviolet photocatalytic oxidation (UV-PCO): Using ultraviolet light to energize a catalyst, electrons are released and interact with water in the air stream, creating hydroxyl radicals, which destroy pathogens.

High Efficiency Particulate Air (HEPA) Filters: These remove 99.97 percent of particulates 0.3 microns in size. Spores are 3 to 40 microns in size.

Active airflow along with Integrated Pest Management (IPM) throughout the grow and surrounding areas can aid in your efforts to keep pathogens out of the air and maintain a clean facility from top to bottom. These tips can help.

3. Filter air throughout the whole facility to reduce pathogens and odors. This ensures people’s safety and comfort while reducing pest pressure.

4. Place foot baths/mats strategically throughout the grow to reduce tracking pathogens from outside to inside or from one grow environment to another.

5. Create a “uniform” and wear freshly laundered clothes into grow rooms every day.

6. Keep tools used in other gardens from entering the grow. Grow tools should be used, cleaned and stored at the grow.

7. Preventative maintenance should be completed successfully and in a timely fashion to ensure proper air filtration and that other environmental control systems work correctly.

8. All team members should participate in IPM and voice concerns and ideas for improvement.

Lee Nye is the head grower at Pruf Cultivar. She has a Bachelor of Science in Plant Biology, and previously was a grower at Pleasant View Gardens and D.S. Cole Growers nursery for a combined 15 years.

Prices for greenhouse and outdoor flower deteriorated dramatically in 2018 after a bounteous fall harvest in 2017. Meanwhile, indoor product saw significantly smaller declines in wholesale rates last year, according to data collected by Cannabis Benchmarks.

National quarterly prices in 2018 illustrated the large supplies of greenhouse and outdoor product available in legal cannabis markets. National volume-weighted price for greenhouse products averaged $1,192 per pound in Q1 2018. That dropped by 12 percent to $1,047 per pound in Q2, then fell another 10 percent to $946 per pound in Q3. Outdoor flower saw its going rate average $938 per pound in Q1. It sank 21 percent to $740 per pound in the second quarter, before sliding an additional 6 percent in Q3, to $693 per pound. Both types of sun-grown product saw rates level off in Q4, when greenhouse and outdoor flower averaged $942 and $705 per pound, respectively.

Overall in 2018, annual average prices for greenhouse and outdoor flower saw respective declines of 29 percent and 30 percent compared to 2017’s wholesale averages. The downturns outpaced those of the annual average for indoor flower, which decreased 17 percent in 2018.

Additionally, while rates for indoor product dropped overall last year, weekly prices were observed to stabilize, and in some cases rise, around periods of strong demand (4/20, Labor Day weekend, and the end-of-year holidays). Quarterly prices increased for indoor flower in Q2 and Q4, which was largely due to elevated rates in April and December, respectively. Wholesale rates for greenhouse and outdoor product generally saw little to no respite from their downward trends even when buyers were looking to take in additional supply.

Prices for indoor and greenhouse flower recovered somewhat during Q1 2019. The average prices for both grow types in Q1 2019 were up roughly 3 percent relative to Q4 2018. Meanwhile, outdoor flower’s quarterly average rate for Q1 of this year was down by more than 5 percent from Q4 2018, as another year of good growing conditions on the West Coast led to robust harvests that piled even more inventory onto already ample supplies.

At the end of Q1, national rates for indoor and greenhouse product were up a bit compared to Q4 2018, while the price for outdoor flower has tracked downward slightly.

Adam Koh is the editorial director for Cannabis Benchmarks.

Of all the nutrients provided by growers to stimulate plant growth, nitrogen (N) is needed in the largest quantity.

Thus, meeting the N needs of cannabis is central to developing a successful fertilization strategy. Because of the volumetric importance of N, it is not surprising that symptoms of N deficiencies often are the first to manifest during production and are the most common plant health issue growers see. Symptoms of N deficiencies that cannabis plants can exhibit include pale green lower leaves and lower leaf yellowing, and as symptoms progress, necrosis and plant stunting. All of these symptoms occur when the available N supply is inadequate. Symptoms develop on the lower leaves because N is a mobile element. Plants will move (translocate) N from the lower leaves to the growing tip if inadequate levels are provided. On the opposite end of the spectrum, when N levels are excessive, lower leaf marginal necrosis (burn) occurs.

Nitrogen Management

The concentration of nitrogen plants need corresponds with where the plant is in its development. Here are the N needs of cannabis plants for each life stage, from rooting to flowering.

Rooting

When plants are being propagated as clones, the nutrient reserves in the cutting can be leached out easily with mist or fog. Nutrient reserves could further be depleted if the cutting was taken from an old mother plant, as reserves in stock/mother plants also diminish over time. As such, it is important to supply a dose of essential nutrients to the cuttings to restore the nutrient reserves. Once roots are visible, provide the plants with 50 ppm to 75 ppm of N two to three times per week to help restore the nutrient levels within the cuttings.

Transplant

Smaller clones just transplanted into a container primarily are putting their energy into establishing a root system. Therefore, they require lower levels of N, so beginning a constant liquid fertilization program of 100 ppm to 125 ppm N will help jump-start growth.

Vegetative Fill Out and Pre-Flowering

Once the roots have reached the edge of the pot and the root system has developed, the plant will start producing vegetative growth. During periods of rapid vegetative growth, cannabis plants require a higher concentration of N, so initially you can ramp up N to 150 ppm to 200 ppm for every feeding during the vegetative stage, and then 200 ppm to 225 ppm of N can be used for feedings during the pre-flowering stage. This will help ensure that adequate levels of N are provided as the plant bulks up.

Flowering

As with any plant that has terminal flowers (including poinsettias and chrysanthemums), the nutrient demands of a cannabis plant peaks and then decreases throughout the flower period. This makes sense: If the plant is not growing as rapidly, as one can easily measure by the change in plant dry weight, then the amount of N supplied should be dialed back. Thus, a lower level of 100 ppm to 150 ppm of N should be applied at every feeding during peak flowering.

Conducting in-house monitoring of the electrical conductivity (EC) in the substrate (as discussed in the “Nutrient Matters” article in the April issue of Cannabis Business Times) will help ensure that the nutrient levels are adequate, and not limiting or excessive.

Corrective Procedures

A straightforward procedure exists to correct an N deficiency: Simply increase the N supply for one or two applications to help restore the N reserves in the plant. Applying 300 ppm to 400 ppm of N from a balanced fertilizer such as 13-2-13 Cal-Mag will provide all the essential nutrients to the plant. Other alternative complete fertilizers include 17-4-17 Cal-Mag, 17-5-17 Cal-Mag, or 15-5-15 Cal-Mag.

Another option to consider is a dark-weather feed (15-0-15) if only N, potassium (K), and calcium (Ca) are desired. If a higher ammoniacal nitrogen (NH₄-N) concentration and higher phosphorus concentration are desired to boost vegetative growth and fill out, then a fertilizer such as 20-10-20 can be applied. Apply these corrective procedures as a 10-percent flow-through leaching irrigation if the plants are grown in pots. This will stop the progression of deficiency symptoms, but will not reverse any severely affected chlorotic or necrotic leaves.

Having a balanced fertility program at the target N levels during each stage of production will help ensure that your cannabis plants have adequate nutrients and will help avoid the development of lower leaf yellowing.

Brian Whipker, James Turner Smith, Paul Cockson & Hunter Landis are from the Department of Horticultural Science, North Carolina State University, Raleigh, N.C.