Editor's Note: The gray information boxes throughout this article present target ranges of elements for growing cannabis, growth concerns, information on how to interpret test results and suggestions for correcting irrigation water problems.
Water is the single largest input for growing cannabis and therefore an essential resource for growing healthy plants. Plants, by weight, are comprised of 90% to 95% water. Elements in irrigation water can affect plant growth, especially in container-grown plants, due to those plants’ restricted root masses and the high potential for change within the soilless substrate because of its relatively low buffering capacity, or the ability to regulate pH changes. Because of this, it is important to regularly monitor your irrigation water to be sure it is not creating nutrient imbalances and inhibiting plant growth.
Water quality varies depending on the source. The three sources of water growers most commonly use are well water, municipal water, and surface water.
In many areas of North America, well water frequently contains high levels of dissolved elements, especially bicarbonates (HCO3–), calcium (Ca), and magnesium (Mg), which can lead to elevated substrate pH levels and tie up iron (Fe) availability to the plant. These elements are commonly found in areas with limestone bedrock, such as the Great Plains or the Canadian prairie provinces. The chemical composition (pH, electrical conductivity (EC), alkalinity, and dissolved nutrients) of well water also varies with well depth, due to the water being pumped from different aquifers, and can even vary seasonally due to changes in the water table. (More information about alkalinity can be found in the article “How to Control Alkalinity in Greenhouse-Grown Cannabis” in the October 2019 issue of Cannabis Business Times.)
Municipal water obtained from rivers or lakes generally has a lower level of dissolved elements than well water. Because municipalities treat water with chloride (Cl) or fluoride (F) to meet drinking water quality standards, excessively high levels of Cl and F may be present, and can cause leaf margin necrosis (browning and/or death) in susceptible plant species. By law, water treatment plants must monitor the chemical quality of their water, and you can contact your local water treatment plant to obtain test results.
Surface or pond water usually contains lower levels of dissolved elements. Growers should be aware of the chemical composition of their surface water to ensure that they are providing adequate levels of Ca and Mg. In addition, caution should be used to protect the water source from herbicide runoff or pollution, which can be detrimental to plant growth.
Container-grown plants are most frequently limited by imbalances in EC, alkalinity, sodium (Na), and boron (B). High EC levels inhibit seed germination and root growth of both cuttings and established crops. Alkalinity directly influences the pH of the root substrate; as irrigation water alkalinity increases, so does root substrate pH. High levels of Na can antagonize (reduce) the uptake of potassium (K), Ca, and Mg. Leaf necrosis occurs when high levels of B are present in irrigation water. Levels of nitrate-nitrogen (NO3-N), phosphorus (P), K, Ca, Mg, sulfur (S), copper (Cu), iron (Fe), manganese (Mn), Cl, F, and zinc (Zn) are rarely a problem in irrigation water.
Testing your water source’s chemical composition annually is a good production practice for cannabis growers to consider. Because of the potential for water quality to change with the seasons, also consider sampling quarterly for the first one to two years to establish a baseline of how your values change over time, especially if you are irrigating with well water.
Irrigation Water Sampling Procedure
To obtain a water sample for evaluation, follow this general procedure (illustrated above):
Run your irrigation line for about 5 minutes to clear the line of impurities.
Label a 500 mL container, such as a rinsed plastic water bottle or lab-issued sampling bottle, with your name and/or operation name, address, water source, and analysis requested.
Rinse the bottle two or three times with the irrigation water to be sampled.
Fill the plastic water bottle, cap it, and then seal the cap in place with tape.
Provide all requested information on lab-issued documents, and submit it to a commercial laboratory for analysis within 24 hours.
Testing labs may have their own submission procedures, so it is important to ask about their practices before submitting the sample.
The target ranges of elements for growing cannabis, growth concerns, information on how to interpret these test results and suggestions for correcting irrigation water problems are presented in the gray columns throughout this article.
With water being the single largest input used for growing a cannabis crop, knowing the quality of that input is important to ensure your nutritional program is on track.
Dr. Brian E. Whipker is a professor of floriculture at North Carolina State University specializing in plant nutrition, plant growth regulators and diagnostics. During the past two years, he co-authored eight scientific journal articles on the impact of fertilization with greenhouse species and three disorder diagnostic guides. Dr. Whipker has more than 28 years of greenhouse experience working with growers.
Paul Cockson is a graduate research and teaching assistant at North Carolina State University. He has a degree in plant and soil sciences with a concentration in agroecology. For the past few years, he has worked in the plant nutrition lab at NCSU with Dr. Brian Whipker.
Patrick Veazie is an undergraduate researcher at North Carolina State University.
David Logan is an undergraduate research assistant at North Carolina State University.
Dr. W. Garrett Owen is an assistant professor and extension specialist of floriculture, greenhouse, and controlled-environment crop production in the Department of Horticulture at the University of Kentucky.
The Carbon Emission Impacts of Greenhouse Cultivation
Columns - Guest Column
New research examines energy sources and CO2 emissions of greenhouse and indoor facilities, and the role climate plays in overall sustainability.
This article is the third in a five-part series by Resource Innovation Institute (RII), a nonprofit that works to advance resource efficiency in cannabis cultivation. In Part I of the series (available at bit.ly/CBT_Resource_Guides), we introduced the “LED Lighting for Cannabis Cultivation and Controlled Environment Agriculture Best Practices Guide” and “HVAC for Cannabis Cultivation and Controlled Environment Agriculture Best Practices Guide,” which were examined by 29 peer reviewers. Key terms introduced in the article are italicized and described in more detail in the guides at ResourceInnovation.org/Resources.
The next two series installments will feature snippets from RII’s Best Practices Guides to highlight more important considerations for growers and the supply chains serving them.
Reducing production costs by optimizing resource efficiency and conveying that sustainability story are becoming central factors in the valuation of cannabis cultivation operations.
While the controlled-environment cultivation industry does not yet have enough information to fully understand the energy consumption of grow facilities using various methods and equipment, recent research reveals new insights into the carbon impacts of cultivating cannabis in greenhouse environments.
How Do Greenhouses Operate?
Many consider greenhouses an environmentally superior and less energy-intensive way to grow plants because natural light can be used for a portion of the grower’s target daily light integral (DLI) for their cultivars. However, there are trade-offs with heating energy use, building envelope integrity and quality, and environmental control with greenhouses due to their unique construction.
When greenhouse building envelopes are designed to let in the sun, they incorporate materials and construction methods that make them more sensitive to their location’s ambient conditions than indoor facilities. Their geographic latitude impacts the length and strength of available daylight, and ambient conditions include outdoor air temperature and relative humidity (RH).
“Greenhouses” can take many forms. From ventilated polycarbonate structures with no thermal curtains to tightly sealed and well-insulated, high-performance buildings with large skylights, these facilities can range widely in how they perform in various climates.
Infiltration, when outside air enters a building, is higher in ventilated greenhouses and lower in sealed greenhouses. Higher infiltration in ventilated structures makes them more sensitive to outdoor temperatures and humidity than sealed structures. The primary driver of infiltration is how leaky the construction is. Outdoor temperature plays a role, as does greenhouse size, but those influences can be all but eliminated if the envelope is well sealed.
Infiltration can be measured using the air leakage rate in air changes per hour (ACH); a lower ACH means less infiltration of outdoor air into a building. For example, an ACH under 1 means a half air change per hour. According to RII research and industry data, sealed and ventilated greenhouses may have these infiltration rates:
Sealed greenhouses: 0.3 – 0.5 ACH
Average ventilated greenhouses: 0.5 – 3.0 ACH
Leaky ventilated greenhouses: 3.0 – 6.0+ ACH
How Greenhouses Use Energy
Like most cannabis operations, greenhouses in colder climates use energy primarily for horticultural lighting. Energy also is used for heating, ventilation, air conditioning (HVAC), dehumidification and the control systems responsible for maintaining target environmental conditions.
Cultivation processes are generally exothermic, meaning they need to reject excess heat into the outside environment.
Several sensible (dry) loads and latent (wet) heat loads, the amount of heat and moisture, respectively, need to be removed from greenhouse air to attain optimal conditions:
Passive solar heat gain: The sun adds sensible heat regardless of whether facilities are ventilated or sealed.
Building envelope: How leaky or well-insulated a greenhouse is substantially affects sensible heating loads in colder climates where weather conditions are more extreme. In warmer climates, poor building envelope integrity can also impact latent heating loads.
Evapotranspiration: The moisture from both plant transpiration and evaporation from water in cultivation spaces is a large source of latent heat.
Horticultural lighting: Lighting is both an energy end-use and a source of sensible heat.
Temperature Controls for Greenhouse Environments
The environments inside both ventilated and sealed greenhouses traditionally are controlled using both hydronic (water-based) and convective (air-based) HVAC systems. Most greenhouse heating systems use fuel, not electricity; typical heating equipment used includes unit heaters, under-bench heating, forced hot air, and radiant heating systems.
Ventilated greenhouses: Traditional ventilated greenhouses use end-wall ventilation fans operated in stages and evaporative cooling wall systems installed on the wall opposite the ventilation fans. These systems pump water onto pads, and as air passes through the media, it is cooled via evaporation. Ventilation equipment and/or roof vents are typically employed to reduce humidity and cool cultivation spaces, and dehumidification equipment is not commonly employed.
It can be a challenge to meet target environmental conditions with coarse controls because many ventilated greenhouses rely on outdoor air and relatively simple fan systems for cooling and dehumidification. Because ventilated greenhouses do not often use mechanical cooling or dehumidification equipment, cultivators are unable to precisely control the conditions to the varying environmental targets for different weeks of flowering.
Field data demonstrates operating conditions regularly vary +/- 10 degrees F from the target temperatures and 10 percentage points from the target relative humidity values. Temperature differences of 7 degrees F have been recorded between the intake and fan (exhaust) ends of the same greenhouse bay, meaning cultivars are experiencing wide temperature variation across cultivation spaces.
Sealed greenhouses: High-performance sealed greenhouses use much different equipment for HVAC and dehumidification due to their sealed nature. While these greenhouses benefit from sunlight (compared to indoor facilities) and improved environmental control (compared to ventilated greenhouses), they must manage solar heat gain using mechanical systems. These tightly built facilities use mechanical cooling systems similar to those used by indoor operations, including commercial-grade hydronic and convective cooling systems. Sealed greenhouses also dehumidify using the same equipment as indoor facilities, such as standalone portable dehumidifiers and integrated HVAC and dehumidification (HVACD) systems. HVACD systems can provide conditioned air to better match the loads of the space, providing greater environmental control. Centralized HVACD systems can leverage sophisticated automation systems, providing precise control of supply air conditions to match the dynamic loads of the space.
Sealed greenhouses are more capable of achieving target environmental conditions because they make use of mechanical cooling and dehumidification equipment, more sophisticated HVACD controls and strategies, and are less sensitive to ambient conditions due to less outdoor air infiltration and better thermal performance than ventilated greenhouses.
Sealed greenhouses can also operate with enriched CO2 atmospheres (because they are sealed), while ventilated greenhouses can only hope to introduce supplemental CO2 during cold weather months, when ventilation is reduced or eliminated as cooling needs are reduced. However, reducing ventilation to either preserve heating energy or operate enriched CO2 can often result in high humidity.
The Greenhouse vs. Indoor Energy Mix
A year-long study of cultivation facilities in Boulder, Colo., assessed how greenhouses use energy. The study gathered electricity consumption and demand data of several greenhouses at 15-minute intervals; monthly energy bills and fuel delivery data; and annual production data, along with a complete inventory of facility equipment and modeling.
The study compared Boulder’s facilities to the performance of indoor and greenhouse facilities in RII’s Cannabis PowerScore Ranked Data Set across North America to understand how greenhouses compared to indoor operations when measuring energy and carbon emissions impacts. The researchers found greenhouses in Boulder typically use less electricity and more fossil fuel on average than indoor operations (which should hold true for greenhouses operating in other cold climates).
Figure 1 shows the breakdown of energy use from electricity and all fuels used in different systems in Boulder greenhouse facilities. Natural gas consumed by greenhouses in colder climates for heating loads, on average, can make up 47% of the total MMBtu, with electricity used to power the lighting, HVAC, fans and other production area systems accounting for the other 53%. When looking at greenhouse electricity use only, lighting energy load was found to account for 61% of greenhouse electric energy use, with HVAC energy loads driving 29% of greenhouse electricity consumption.
Figure 2 shows the breakdown of energy use allocated to different systems in Boulder indoor facilities. Natural gas can make up as little as 2% of the total MMBtu consumed by indoor operations in colder climates, with electricity for lighting driving 69% of total energy use, compared to 32% for greenhouses. HVAC energy loads contribute nearly the same amount in indoor and greenhouse facilities.
Because greenhouses use sunlight for plant cultivation, electricity demand can be reduced in the middle of the day as solar radiation increases. The peak electric load from greenhouses in the Boulder study was recorded between 8 a.m. and 9 a.m., when electric lighting is turned on, but the morning sunlight is still intensifying. Once the sun sets, electric load increases again until lights are shut off overnight. Facility electric load is intimately linked to solar radiation, and generally as solar radiation increases, greenhouse electric demand decreases.
Greenhouse gas (GHG) emissions from fuel consumption are higher for greenhouses in colder climates. When greenhouses use fuel-based heating systems, as the Boulder greenhouses do, when heating degree days increase (meaning the facility experiences more hours of colder weather), natural gas consumption increases. The amount of cold weather and fuel used may change depending on where the greenhouse is located, but the relationship between greenhouse fuel use and outdoor conditions will always exist.
How Do We Measure Sustainability?
How do we define and measure cannabis cultivation operations’ sustainability, and determine which operations are the most environmentally friendly? One important step is to verify or challenge past assumptions using data that is available.
To enhance sustainability claims and business valuation, greenhouse operators, like those of all cultivation facilities, should balance electricity and fuel costs with their carbon impacts. The site-specific GHG emissions from any industrial operation are dictated by the regional electric utility generation assets and grid transmission losses, in addition to the carbon content of delivered fuels used for processes. Some fuels, like propane and fuel oil, have higher GHG emissions (measured using equivalent carbon dioxide (CO2e)) than other fuels, like natural gas. Given the large amount of fuel used by greenhouses, the carbon footprint of this consumption is important to understand.
The Boulder study concluded that, on average:
Greenhouse productivity in grams/MMBtu of site energy was 15% better than the indoor facilities. (Note: Highly efficient indoor cultivation is also possible—the study found the productivity of the best-performing indoor facility was 25% better than the best-performing greenhouse); and
Greenhouse grams/lb. CO2e was 71% better than the indoor facilities.
How is it possible that greenhouse site energy productivity is only 15% better, but the emissions are 71% better? It comes down to the energy mix used on-site, and the fuel used to generate the electricity that serves the facility.
If you were to compare the emissions of two greenhouses with identical site energy productivity, one based in Boulder and one based in Massachusetts, the Massachusetts facility would produce nearly 50% less CO2e. This is due to a large portion of Boulder’s electricity generation coming from coal-fired generation facilities, while Massachusetts electricity is generated largely through renewables and natural gas, according to data from the U.S. Environmental Protection Agency.
We see from this sample of projects that the electric savings achieved through leveraging sunlight and outdoor air ventilation in the cultivation process are largely offset by heating needs in cold-climate ventilated greenhouses. However, while greenhouse facilities’ average productivity in grams/MMBtu of site energy was slightly better than that of indoor facilities, greenhouses’ CO2e emissions were substantially lower. For this geographic region with this electric grid, and viewed through the lens of CO2 emissions, greenhouses far outperform indoor facilities.
Regardless of the location of your greenhouse, high-performance sealed greenhouses can maximize your productivity and reduce your CO2 emissions. It is important to understand the role of geography (infiltration, ambient conditions, sunlight) and the source of electricity serving the facility when assessing the performance and emissions of any new greenhouse facility, or when assessing existing facilities for energy, productivity, or emissions improvements.
Gretchen Schimelpfenig, PE, is the technical director of RII and manages the organization’s Technical Advisory Council.
Nick Collins, PE, is a member of RII’s Technical Advisory Committee and a contributor to the “HVAC Best Practices Guide.”
Machine Trimming Cannabis: 4 Tips From Nevada's Solaris Farms
Departments - Upfront | Quick Tips
Reduce labor costs and human error by following these steps.
Finding efficiencies that will reduce labor costs and human error is an everyday consideration for any crop, but especially cannabis. One of the most challenging aspects of cannabis cultivation is the post-harvest process of trimming, where maintaining efficiency and minimizing human error and contamination are difficult.
Hand trimming and processing is also one of the most time-consuming aspects of operating a cultivation business, with one person typically finishing a pound or two a day. Trimming by hand is also tedious and repetitive work that is prone to human error, especially when done over a long shift. As an operation that produces more than 500 pounds of product per month, Solaris Farms considers automating this step a necessity.
The demand for fast and safe machinery to address this niche has boomed. Commercially available trimming machines vary in size, efficiency, cost, and quality, but many can process several pounds in an hour. Here are some considerations for growers interested in machine trimming.
1. Find a machine that can sort by flower grade.
Once the buds are picked and dried, the post-harvest process starts with a good sorting: separate “A-grade” buds from less-desirable buds like popcorn and trim to carefully remove leafy matter from the “A buds” and preserve their trichomes. Most machine models today function simultaneously as both separators and trimmers, which can help growers increase efficiency.
2. Use non-stick tumblers and adjust blades to cut waste.
Efficient trimmers include those that tumble the product and snip the extra leaves as they tumble through machine-like rollers; others include trimmers that lay the product horizontally and gently snip the extra leaves through gravitational force.
Growers can minimize trichome loss and/or wasted product by using machines with non-stick tumblers. Readjusting the blades so they aren't too close may also mitigate slicing off chunks of bud by accident. The models are designed based on volume, with smaller-volume trimmers utilizing slow, fine-cut blades, and bulk-sized trimmers utilizing faster, larger blades.
3. Attach extensions for popcorn and trim.
Trimming machines generally include some sort of tumbler or drum with a grate that the full flower is added to. The buds then are tumbled apart from leaves and shake, and the buds get trimmed by a blade or blades. Although “A buds” should have a subsequent hand finish, it is not always possible in industrial settings.
A gentle machine with a slow rotation, fine-cut blades and no extensions works great for your “A-grade” buds destined to be sold as flower, whereas machine extensions can allow growers to more quickly, and using less labor, tumble out popcorn for bagged flower and pre-roll sales and trim for processing. This will allow your post-harvest staff to concentrate their time and energy on finishing higher-end buds to make sure they have bag appeal while moving through your harvest cycles in an efficient manner.
4. Regularly clean and maintain trimming machines.
While automation is safer than trimming by hand when it comes to the potential for introducing pathogens, trimming machines should generally be cleaned and maintained between each batch to avoid excess build-up on the blades. This is necessary to maintain cleanliness and efficiency. Every model will have its own unique cleaning process, but in most cases, resin can be removed using soap and hot water, alcohol, or other organic cleaners.
Then, in late June of this year, a DOJ whistleblower testified before a U.S. House committee that Attorney General William Barr had launched some of those antitrust investigations because of a personal dislike for the cannabis industry. In other words, there was a political motivation behind the sudden scrutiny, according to John Elias, a career DOJ employee.
"Rejecting the analysis of career staff, Attorney General Barr ordered the Antitrust Division to issue Second Request subpoenas," Elias said in his testimony, citing 10 mergers or acquisitions that received an extra look from the DOJ. "The rationale for doing so centered not on an antitrust analysis, but because he did not like the nature of their underlying business. … For context, these kinds of investigations are rare: On average, only 1% to 2% of the thousands of transactions that come before the Division each year get a full review."
So, what does this mean?
For one, we can’t turn back the clock. Multistate operators have already felt the cooling effect of antitrust investigations. It’s less the substance of the scrutiny than the destabilizing nature of new federal compliance. Antitrust reviews delayed many large cannabis deals last year, forcing businesses to renegotiate terms in an uncertain marketplace while the DOJ sniffed out the contract. Cresco Labs, for example, watched the stock value of its purchase halve while waiting for the deal to close. A proposed $682-million merger between MedMen and PharmaCann was terminated in October 2019.
As of mid-July, this matter is far from over in Congress. Two U.S. House reps filed a resolution in favor of impeaching Barr, citing, among other reasons, his overzealous sightlines on the cannabis industry.
While Barr remains in office, will we see more of these antitrust investigations in the otherwise federally illegal cannabis space? It’s hard to say. M&A activity has been a slog this year: 36 deals closed through the first half of the year, compared with 290 in all of 2019, according to data from Viridian Capital Advisors. Growth capital is still tough to find, outside of new robust special purpose acquisition corporations (SPACs) working the market. These trends make the sorts of mid-sized business combinations and public-company stock moves that swept through the industry in 2018 and early 2019 all the more palatable for companies interested in expansion.
In a Viridian Capital report that ushered in 2020, the firm stated, “There is a market shift toward stock-for-stock mergers versus cash-based acquisitions in order to achieve economies of scale while preserving cash.” Sounds like the Cresco deal. And based on what we’ve seen thus far in 2020, it seems to be where the industry is headed.
Eric Sandy is digital editor for Cannabis Business Times, Cannabis Dispensary and Hemp Grower.
6 Tips for Managing Humidity in Indoor Cannabis Cultivation Facilities
Departments - Upfront | Quick Tips
How to optimize humidity in cannabis cultivation operations to increase growth and minimize diseases and pests.
Managing the humidity levels in a cultivation operation is absolutely critical to maintaining a growth schedule and getting optimal production out of plants. If humidity levels creep too low during the vegetative growth phase, plants will be stunted, and you will lose weeks of production waiting for them to pull through. If humidity is too high, you are at risk for disease outbreaks, including the infamous bud rot.
Here are six tips to help you better manage cultivation facility humidity.
1. Track indoor and outdoor environmental data.
Humidity changes inside a grow are not dependent upon just the actual relative humidity (RH) of the incoming air, but also the grow room temperature. Many cultivators have struggled because they have taken plans from a cultivation operation in California or another western state and dropped them into the Midwest or Northeast without accounting for the differences in ambient outdoor conditions. Tracking outside environmental data throughout the year is the best way to anticipate patterns and make changes in advance.
2. Steam your way through veg.
Plants like a lot of humidity in the vegetative growth phase. Of course, each cultivar likes a slightly different environment, but generally speaking, at our Galenas facility in Akron, Ohio, we keep relative humidity around 65% to maximize transpiration and keep plants healthy and growing at their maximum rate. This humidity level keeps the plant’s stomata open, which keeps water and nutrients pulling up through the plants. Nutrient mobility is the key to healthy plants.
3. Stage your dehumidifiers based on other environmental changes.
Humidity levels tend to spike right after the lights go off. One way to offset this spike is to ramp up dehumidifiers from a half hour before to a half hour after lights turn off. Pay attention to those environmental logs.
4. Transition gradually.
Plants can tolerate lower humidity as they move through the flowering period. We like to keep our RH at 65% for the first week of flower. This minimizes plant stress during a naturally stressful part of their life cycle. Between weeks three and eight, we gradually lower the RH.
5. Avoid swings to prevent disease.
Sporulation of powdery mildew can occur if there are large swings in humidity. Avoid creating humidity from flood-style watering, and make sure to remove any standing water if overflows or leaks in irrigation systems occur.
6. Work with your product manufacturers.
We use LED lights throughout our facility, and the supplier provided a cultivation guide. It provides mounting heights and dimming percentages at specific distances, as well as temperature, photosynthetic photon flux density (PPFD), CO2 and RH management guidelines. Also included is a great Vapor Pressure Deficit chart.
Geoff Korff is founder and CEO of Galenas, a Level II cultivator in Ohio’s medical cannabis program, operating out of Akron. Christine DeJesus is director of cultivation at Galenas.
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