Green Weed, Green Planet

Tyler Clements (Environmental Science), Rudy Marek (Geology), Mitch Maslanka (Natural Resource Conservation), Olivia Santamaria (Horticulture)

In 1996, California voted to become the first state to legalize marijuana for medical use. Fast forward to today, and the legalization of marijuana is now a seemingly unstoppable movement that is sweeping across the United States. With recreational and medicinal use being rapidly legalized all over the country, 29 states have already legalized marijuana medicinally and 9 have recreationally (Robinson, Berk, & Gould, 2018, para. 2). From the start of California legalizing marijuana, this new industry with seemingly endless potential was given the green light to begin at the commercial level. As of 2017, the industry has grown from $6.73 billion to $9.7 billion in North America (Borchardt, 2017, para. 1; Robinson, 2018, para. 6; Zhang, 2017, para. 2). The entrepreneurs of the country began to think of ways to create and expand a marijuana based business and one of the most important aspects of this process was how the marijuana itself was going to be grown.

As legalization of marijuana continues to spread through the United States, its environmental impact continues to grow. The U.S. is currently responsible for 90% of cannabis sales worldwide (Zhang, 2017, para. 2). This increase in demand has caused marijuana agriculture to use increasing amounts of resources that food agriculture already depends on, increasing its environmental impact. In order to meet this growing business, there needs to be an agricultural system that can meet the requirements to grow marijuana while also limiting its environmental impact. The two main systems to grow marijuana are open field and greenhouse agriculture, however each has their own advantages and disadvantages. Because of both production systems’ abilities to negatively impact the environment, there needs to be a way to alter production strategies to provide an agricultural system that can meet the growing demand for marijuana, while also doing so as environmentally friendly as possible.

The two main methods used to grow marijuana commercially, open field and greenhouse production, vary greatly in how they operate. Open field production consists of growing crops outdoors in fields, meaning their operation depends heavily on the weather and climate. Greenhouses are buildings, generally made of glass or poly-carbonate, that allow natural sunlight to enter and trap heat inside. The plants are watered and fed nutrients in controlled amounts to assure the plants will grow fast and healthy. During colder times of the year, especially wintertime in the northern U.S., greenhouses are still able to function, unlike open field production. In order to achieve this, additional heating is needed because the sun isn’t producing enough heat and light to keep plants alive. In order to provide enough light to the plants during these winter months, greenhouses use supplemental (artificial) lighting in addition to the natural lighting so the plants still obtain enough light to flourish (Mbakahya, 2016). Because of these differing production styles, their effect on the environment varies as well.

When comparing these environmental impacts of both production systems, greenhouses end up being the better option. The irrigation techniques of open field systems tend to be very wasteful, and lead to soil erosion (Khoshnevisan, Shariati, Rafiee, & Mousazadeh, 2013). This is particularly concerning as marijuana requires around 22.7 liters of water every day per plant (Bauer et al., 2015, p. 11). In greenhouses, specifically hydroponic greenhouses, water can be controlled so each plant can be provided exactly what it needs, reducing wastewater. Throughout the lifespan of the plant, this can save up to 70% of the water needed to make the plant grow (Butsic & Brenner, 2016, p. 8). Both of these methods require fertilizer which can be harmful if leached into the environment. Greenhouses require a greater amount of fertilizer than open field systems, but being in a contained system helps prevent the fertilizer from being leached into the environment, whereas open fields have less control over where the fertilizer goes, leading to more leaching (Boulard et al., 2011). Open fields have a similar issue with pesticides as again it is difficult to control where the pesticides go in an open environment. They also use significantly more pesticides than greenhouses, whereas greenhouses are able to use more non-chemical pest treatments (Boulard et al., 2011; Romero-Gamez, Antón, Leyva, & Suárez-Rey, 2016). Open fields also require massive amounts of land that many areas cannot afford to provide. Greenhouses take a fraction of the land to produce the same amount of product (Charles, 2015; Khoshnevisan et al., 2013, p. 320; Mbakahya, 2016). This makes them perfect for growing throughout the United States as they can be near the areas that the demand is greatest without taking up a lot of space or impacting the environment as much as open field production.

Not only are greenhouses more environmentally friendly, they are also better able to meet the growing demand for quality marijuana. Marijuana is a plant that needs a significant amount of light and heat to grow effectively. In higher latitudes such as the northern United States, the air is cold and periods of sunlight are short in the wintertime, making it impossible to grow marijuana year round in an open field, as the early growing phases of marijuana require 18-24 hours of light to grow efficiently (Haze, 2018, para. 1). Greenhouses however, can solve this issue with their ability to provide 24 hour light as well as supplemental heating. By heating the greenhouse and using supplemental lighting, they are able to achieve the specific growing conditions needed for marijuana. This not only means continuous year round production, but also higher quality marijuana due to their optimal growing conditions (Charles, 2015; Mbakahya, 2016). Generally natural gas or propane is burned in furnaces to heat and light the greenhouse, releasing greenhouse gases like carbon dioxide, and contributing to global warming (Khoshnevisan et al., 2013). However, because of these heating and lighting systems greenhouses are able to produce all 12 months out of the year, as opposed to open field systems that can only operate a select few months out of the year. Because of this year-round production, greenhouses are able to produce significantly more than traditional open field production (Charles, 2015; Khoshnevisan et al., 2013; Mbakahya, 2016). Greenhouses are capable of producing 10 to 20 times more product per acre than open field (Charles, 2015, para. 11; Khoshnevisan et al., 2013, p. 320). This higher yield combined with the ability to grow year-round will allow growers to keep up with the demand of marijuana (Mbakahya, 2016). Whichever production system is being used to grow marijuana for the years to come need to be able to produce enough while also be as sustainable as possible, and greenhouses fit both of those criteria.

While greenhouses have the advantage of increased yield, reduced soil erosion, reduced water, fertilizer, and pesticide pollution, and are geographically adaptable, they unfortunately consume more energy than open field production. Heating the greenhouse to create the proper environment for growing consumes nearly 95% of the total energy used (Boulard et al., 2011, p. 762). Compared to open field methods, greenhouses consume 38% more energy, with 87% of that energy coming from diesel fuel and natural gas (Khoshnevisan et al., 2013, p. 319). One study showed that 90% of the heat sources for greenhouses were from natural gas (Boulard et al., 2011, p. 762). This heating is important however, because marijuana plants require temperatures between 20 – 30°C in early phases and then slightly lower temperatures, 18 – 26°C, when flowering (Haze, 2018, para. 4). In Colorado, a state where marijuana is recreationally and medicinally legal, the average temperature during the winter months of December to February is only 7.5°C (U.S. Climate Data, n.d.). Having the right temperature promotes faster growing as well as a higher THC content (Haze, 2018). Below 15°C, plant growth is slowed and at freezing temperatures the plants will die quickly (Haze, 2018, para.1). High temperatures, above 30oC, will also cause plant growth to slow but also promote the growth of pests, such as spider mites (Haze, 2018, para.1). Greenhouses are a much better fit for marijuana growing because they can achieve these specific temperatures through the use of their heating systems.

Marijuana also requires a significant amount of light, 18 – 24 hours when starting and 12 -14 hours when flowering (Haze, 2018, para.1). Greenhouses can provide these light cycles due to their supplemental (artificial) lighting, whereas open field growing does not have control over the amount of light a plant can get in a day. Because of this there is a significant need for heating and supplemental lighting in greenhouses which also requires large amount of electricity. In 2014, marijuana used 2% of all the energy used in Denver, Colorado (Sevcenko, 2016, para. 5). One facility in particular used 29,000 kilowatt hours(kWh). The average household in the county used about 630 kWh (Sevcenko, 2016, para. 11). Colorado did push for clean energy as Boulder County required marijuana growers to offset their energy use through renewable resources and if they didn’t, they’d have to pay an extra 2 cents per kWh (Sevcenko, 2016, para. 11). For the grower using 29,000 kWh, that’s an extra $580 every month. But in an industry worth $9.7 billion, the product grown will make more than enough profits to compensate for that (Robinson, 2018, para. 6). In turn, this high electricity usage can lead to negative environmental impacts if the energy is obtained from fossil fuels.

Due to the high amount of energy consumed by greenhouses for heating and lighting, they produce large amounts of emissions, making them one of the top contributors to greenhouse gas emissions in the agriculture industry (Khoshnevisan et al., 2013). Greenhouse gas emissions are comprised of three types of gases: carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) (Bos, Haan, Sukkel, & Schils, 2014). Greenhouses can produce 43 times more CO2 than open field (Khoshnevisan et al., 2013, p. 320). The same study comparing strawberry production of both systems concluded that on average, greenhouses produced 3.29 times more CO2 per strawberry than open field. This was due to their use of natural gas and electricity, with one of the main reasons for the use of both energy sources being for heaters (Khoshnevisan et al., 2013, p. 320). Other studies have also shown that heavy fuel (oil) is the main cause of high emissions in greenhouses, with one study showing fossil fuels were 50-85% of the contributors towards ozone depletion and global warming in Canadian greenhouse production. (Soode-Schimonsky, Richter, & Weber-Blaschke, 2017, p. 571-572). It can then be concluded that the main problem with greenhouses is their high energy use, which is due to the need of heating mechanisms that consume fossil fuels which in turn emit high amounts of greenhouse gases into the atmosphere. Luckily, these high amounts of emissions can be lowered through the replacement of fossil fuels with biofuels.

Biofuels are fuels that are derived from biomass such as trees, agricultural wastes, crops, or grasses (Oak, 2016, para. 2). Within the biomass there are certain chemicals that can be changed into the biofuel such as ethanol. This is just like how bees go out and collect pollen to turn into their food (fuel). By doing this they are able to survive every year by what nature is providing. On the other hand, there are animals who look for these large food (fuel) deposits and destroy them for the quick gain of food. As this progresses there are fewer and fewer food deposits available. This is just like people today looking for fossil fuels underground instead of seeking the never ending supply they are standing on. These biofuels can be used to replace conventional fossil fuels such as petroleum, propane, coal, and natural gas (Oak, 2016, para. 2). The biofuels don’t require a whole new piece of machinery to be burned but do require some of the parts in the machinery to be switched. The newly created biofuels are more environmentally friendly as they produce fewer greenhouse gases than fossil fuels (Lippke et al., 2012, p. 298). Some forms of biomass, such as corn, need to undergo some changes before it can be used as biofuel. Sugar or starch needs to be extracted from corn and fermented into ethanol which can then be burned in a furnace to heat a greenhouse. All of the material used in these processes are sources that can be replenished rapidly (Oak, 2016, para. 3). Since the raw materials can be replenished quicker than fossil fuels, there is no need to worry about running out of biofuels like there is for fossil fuels.

There is a substantial variation in the range of biofuel emission reduction that results from the different biofuel choices, but it is abundantly clear that biofuels produce less emissions than fossil fuels (Lippke et al., 2012, p. 299). Burning and collecting fossil fuels directly releases large amounts of carbon and other greenhouse gas emissions into the environment. Using wood and biofuel feedstock instead of fossil fuels will help to minimize the greenhouse gas (GHG) emissions created from burning fossil fuels. This is possible because these fuels are created with far less carbon emissions and are able to burn with less emissions. GHG emissions can be reduced by about 60-128% when biofuels are used to power equipment instead of fossil fuels (Lippke et al., 2012, p. 299). Cord wood, a type of biofuel, can reduce GHG emissions by up to 74% (Lippke et al., 2012, p. 299). When the carbon uptake (amount of carbon stored through growing process) stored in a lumber product is brought into consideration, fossil fuel emissions may be reduced by as much as 497% (Lippke et al., 2012, p. 300). By using wood this way, less emissions will be released than if the wood was left for disposal and decomposition. The use of biofuel feedstock has a greater potential for emission reduction.  Ethanol fermentation can reduce emissions by 128% while ethanol gasification (the process of turning a liquid into a gas) can reduce emissions by 74% (Lippke et al., 2012, p. 299). Ethanol can also be produced from lower grade waste wood. Ethanol is produced from other types of biomass, such as corn. Corn is grown in large amounts all over the world. This makes corn an easy resource to use for more biofuel. Over a ten-year period (2005 – 2015), the production of corn-based ethanol is approximately 43 percent lower than gasoline and if improved, corn-based ethanol could reduce our GHG emissions by about 50% (Environmental and Energy Study Institute, 2017, para. 1). That is just in regards to the production of the actual fuel. When the fuels are then used, it has been found that corn-based ethanol can reduce GHG emissions by an additional 19 to 48 percent, depending on farm management and practices at the ethanol plant (Environmental and Energy Study Institute, 2017, para. 3). The amount of fossil fuel emission reduction remains similar across the liquid fuel alternatives. The reduction amounts are about 60 and 70% which is above the EPA average for emission reduction (Lippke et al., 2012, p. 301). This is especially true in urban areas as GHG emissions created from biofuels are more climate friendly than petroleum fuels. This can be seen in a study conducted on several different blends of biofuels. The results show that carbon dioxide reductions of 26% can be achieved when the right blend of biofuels is found (Hashimab et al., 2017, p. 217). Some scientists have even found that by about 2050, biofuels could reduce our greenhouse gas emissions by 1.7 billion tons per year, which is equivalent to more than 80% of current transportation-related emissions (Oak, 2016, para. 7).

Biofuels such as wood and corn have the potential to be a more sustainable fuel for greenhouses. For example, wood can replace fossil fuels because of its low cost, high heat value, and renewable availability and even cheap waste wood can be used to heat a greenhouse. To make the most out of wood fuel, it’s important to understand which type of wood is most efficient, as energy outputs are heavily affected by the moisture content and type of wood used. Hardwood gives off twice the amount of heat or Btu/lb as softwood does. British thermal units per pound (Btu/lb) are used to measure energy output amounts per pound of wood. Moisture content (mc) is the amount of water held in a piece of wood . A piece of wet wood (50% mc) will release 4,700 Btu/lb where as a dry piece of wood (20% mc) will release about 1.3  times more heat at 6,200 Btu/lb (Bartok, 2007b, para. 4). Using wet wood attenuates the practicality of using wood as an alternative fuel source because it’s not heating the greenhouse in the most efficient way. These same concepts apply to wood chips as well; dry hardwood chips will release more energy than wet softwood chips (Bartok, 2007b). Compared to oil, wood is much less expensive, costing almost 6 times less to run the same sized greenhouse. Also, when wood is burned at a high temperature, it releases less smoke and air pollution than fossil fuels (Bartok, 2007a). For these reasons, wood can be an effective, cheap, and more environmentally friendly fuel source than fossil fuels.

Biofuels seem like a great way to replace fossil fuels, however biofuels need to be cost effective. Getting a cost for any biofuel is difficult as prices will vary with the production volume, process, food prices, and more (The Cost of Biofuels, n.d., para. 10). Any place that offers biofuel is trying to keep the price per gallon about the same as that of a gallon of fossil fuels (The Cost of Biofuels, n.d., para. 12). Some governments that are trying to get cleaner energy are helping biofuels stay cost effective. The Energy Information Administration (EIA) is a branch of the U.S. department of Energy whose sole purpose is to help mitigate costs of energy and implement policies to maintain a fair market. For example, the EIA estimates that the cost for a biodiesel made out of soybean oil for 2012/2013 will be about $2.06 per gallon if 50 million gallons are produced and about $2.47 per gallon if 200 million gallons are produced (U.S. Department of Energy, 2018, para. 5). In both of these cases the biodiesel remains less expensive that the average fossil fuel. The U.S. Department of Energy keeps a chart of current costs for different fuels across the nation. The most updated chart is for the month of January 2018 and shows that biodiesels cost about $2.48-3.48. When compared to the current cost of propane, $2.83, gasoline, $2.50, and diesel, $2.96, biofuels seem to be equal to or slightly more expensive than what we are already paying for (U.S. Department of Energy, 2018, para. 5). This may seem bad at first but we need to see that biofuels will never run out and their production costs can be brought down if there is a way to increase the amount of biomass created when farming.

For many farmers, seeing the expensive up-front cost to begin a new biofuel heated greenhouse system can be a huge turnoff. A typical outdoor wood furnace costs between $2,000 and $10,000 depending on the size of the greenhouse; installation and accessory system parts can add on another $3,000- $15,000 (Grubinger, 2008, p. 2; Nature’s Comfort, 2018; Outdoor wood, n.d.). Natural gas furnaces can cost as low as $700 which is almost 3 times lower than the cheapest wood furnace (HomeAdvisor, 2018a). Wood furnaces are a big price tag considering the value of a 500 square foot greenhouse is about $12,000 (HomeAdvisor, 2018b). The benefit of buying the wood furnace is that it will be paid off in as short as 3.5 years because of the money saved on petroleum or natural gas (Grubinger, 2008, p. 3). In order to persuade growers to convert or begin a biofuel heated greenhouse, subsidies should be put in place by the government to benefit biofuel sources and reduce the desire to use fossil fuels. The U.S. Department of Agriculture (USDA), which already presents agricultural subsidies, would present financial aid to biofuel companies to make their furnace systems cheaper than fossil fuel based systems. If wood and ethanol furnaces are subsidized, initial set-up costs to operate a biofuel run greenhouse will be lower. Greenhouse operators will notice the lower costs and buy the cheaper option (the subsidized biofuel equipment) rather than the now more expensive fossil fuel furnaces. These subsidies will transition greenhouses to a more environmentally friendly way of heating themselves. Taxes should also be reduced on land for greenhouse operators who are willing to switch to biofuels and grow their own biomass for fuel i.e. trees for wood. The USDA already subsidizes growing corn, so there is no need to add more support in growing this fuel type (USDA, n.d.). If the USDA awards these subsidies, marijuana growers will be able to heat their greenhouses for a more affordable cost while also lowering greenhouse gas emissions.

Based on a successful project subsidizing energy sources in the U.S., it is believed that this new plan to subsidize biofuel equipment and reduce land taxes for greenhouses will also be successful. In a report presented by the U.S. Energy Information Administration, details on past subsidies in energy were explained. Between 2010 and 2013, solar energy subsidies increased by $4.2 billion and resulted in a large increase in the installation rate of solar facilities. This subsidy was comprised of grant payments and tax credits (U.S. EIA, 2015, p. 18). With our similar goal of increasing the installation rate of biofuel heating systems, we believe that subsidies in the form of grant payments and tax credits will help achieve our goal. Grant payments will go to biofuel equipment companies to reduce the costs of wood and ethanol furnaces. Tax credits on land will be awarded to greenhouse operators that are willing to switch to biofuels and grow their own fuel. The likelihood of this plan having success is promising considering the U.S. has had previous success subsidising in favor of clean energy.

As marijuana continues to be legalized in the United States, environmental impact must be considered as commercial growing continues to expand. Greenhouses currently use more fossil fuels than open field, but are able to regulate the environment to promote faster growing plants with higher potency (Haze, 2018). The potential to reduce greenhouses environmental impact is higher than open field’s. A greenhouse’s environment is more consistent and predictable than open field where rain and light vary. Open field systems also have higher water usage which leads to soil erosion, leached fertilizers, and heavy pesticide use. The main way to create more sustainable greenhouses is to alter the fuels used to maintain them. By using biofuels, the U.S. can take advantage of the high productivity and predictability of yields from the greenhouses while also achieving a lower impact on the environment.




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  1. Thanks a lot for another comprehensive post, Evan!
    Always good to hear new perspectives on environment protection, especially when it comes to hot topics like this one!
    Best wishes!

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