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Grow Carbon Neutral Cannabis Indoors? [Explained]

Saying that achieving carbon neutrality is one of the most critical challenges that humankind faces in the 21st century is not an understatement. The Paris Agreement of November 2016 pledged for the European Union to achieve it by 2050. It was an essential commitment because of how climate change is impacting the planet. A failure to halt the tide of carbon emissions will have dire consequences for all life on Earth.

The term ‘carbon neutrality’ means having a net-zero carbon footprint. It is the practice of balancing emissions with carbon removal or eliminating emissions. In 2019, CO2 emissions were 33 billion tonnes, more than 150 times the figure from 1850. The carbon dioxide concentrations in the atmosphere are at their highest in more than 800,000 years!

Apart from causing respiratory disease from air pollution, greenhouse gases are beginning to cause havoc with our climate. Melting ice caps and the ensuing rising sea levels threaten countless species, including humans.

Those who champion cannabis often point out how it is a plant that grows ‘naturally.’ One would imagine that the marijuana industry would be among the best for trying to keep carbon emissions down. In reality, the carbon footprint of weed grown indoors is exceptionally high. As the herb becomes legal in more places, the demand increases. It has resulted in a rapid rise in the industry’s carbon footprint.

However, at least there are now concerted attempts to turn the tide. Let’s find out more about the marijuana industry’s carbon footprint and its quest for carbon neutrality.

Cannabis’ Carbon Footprint Is Bigger Than You Think

On a global scale, CO2 emissions have approximately doubled since 1980. Finally, a noticeable number of industries are trying to adopt sustainable practices. The more pessimistic climate change experts suggest it is already too late. However, it is essential not to give up and allow the Earth to fall apart under our watch.

Cannabis is now the #1 energy-consuming crop in the United States!

In North America, a growing number of localities have legalized cannabis. It is entirely legal for adults in Canada, and there are recreational or medicinal marijuana programs in 33 American states plus D.C. The billions of dollars in sales have provided boosts to local economies. Various state governments are rolling in the tax dollars offered by weed. However, many people are completely unaware of the scale of energy use involved in marijuana production.

How Much Energy Does Legal Cannabis Use?

Estimates vary enormously, from 6-580 kilowatt-hours per kilogram in greenhouse growing to 4,400-6,100 kilowatt-hours per kilogram for indoor production. Most papers on the subject cite the work of Evan Mills. He published ‘The Carbon Footprint of Indoor Cannabis Production’ in Energy Policy in 2012.

Back then, Mills claimed that indoor marijuana growing accounted for 1% of America’s entire electricity usage! This equated to 4,600 kilograms of carbon dioxide emissions into the atmosphere per kilogram of weed grown. In dollar terms, it was approximately $6 billion worth of electricity. It is the equivalent CO2 emissions as “3 million average U.S. cars when aggregated across all national production”. It was also akin to powering two million homes for a year.

Growing a single kilogram of weed indoors used the same energy as traveling across the U.S. seven times by car. Cultivating a single joint’s worth at that time was the equivalent of leaving a lightbulb on for 25 hours!

Mills wrote his report almost a decade ago. Has the industry improved in a CO2 emissions sense? Not according to more recent figures. Remember, when Mills published his work, the cannabis sector was a lot smaller than it is now.

In 2018, legal marijuana cultivation used around 1.1 million megawatt-hours of electricity. The industry produced approximately 472,000 tonnes of carbon dioxide emissions. It was a significant decrease on Mills’ figures, but still far too high. Indoor cultivation is 18 times less energy efficient than growing the herb outdoors. You also produce 25 times more CO2 emissions!

On average, a 5,000 square foot facility growing weed indoors uses enough energy to power 66 American households. Furthermore, 4% of all of Denver’s energy consumption came from growing marijuana in 2018!

What Causes the Greatest Level of Emissions?

Lighting is the biggest culprit, accounting for 33% of all energy usage in cannabis production. Ventilation and dehumidifiers are next at 27%. Air conditioning is responsible for another 19%.

The sad reality is that growers will continue to produce their weed indoors. They get the highest yield per square meter and have control over growing conditions. It is also much harder to secure outdoor growing space. States such as Illinois, which permit weed cultivation, have banned growing outdoors.


Large indoor facilities are sadly, extremely unlikely to ever achieve carbon neutrality without massive changes. Even today, a reasonable proportion of growers use high-pressure sodium (HPS). This type of lighting can increase a grow room’s temperature by around 30 degrees Fahrenheit. As a result, the organizations must consistently use heat, ventilation, and air conditioning (HVAC) systems.

Fortunately, an increasing number of commercial growers are becoming more aware of their responsibilities. One expert said there is a 50% difference in carbon emissions between a top-performing operation, and an inefficient one. By making more sensible decisions, the high-ranking firms can buy carbon offsets or renewable energy credits to decrease their carbon footprint even more.

How to Green up Your Growing Operation

The demand for legal cannabis is growing in North America. So is the number of businesses ready to provide the goods. In the United States, cannabis is illegal on a federal level. Therefore, any interventions made must come from individual state governments. Illinois is trying to lead the way in this regard.

It legalized adult-use cannabis in June 2019. Almost immediately, it also implemented a strict set of environmental regulations for marijuana cultivation. Illinois placed limits on how much water and electricity a grower can use. There are also specific requirements regarding wastewater and water runoff.

If you want to grow cannabis in Illinois, you must use an automatic watering system. You are also only allowed to use a maximum of 36 watts per square foot when providing lighting. It is a similar story in Massachusetts, and more states look set to follow suit.

Interested in cultivating cannabis indoors? Here are a few quick tips.

Embrace Water Efficiency

The cannabis plant is a thirsty one. On average, each plant needs 23 liters of water a day and could grow for more than 12 weeks, depending on the strain. You can use autoflowering strains and cut the overall growth time to less than ten weeks.

There are techniques such as reverse osmosis in place to help recycle and reuse water. Some companies have developed hydroponic systems with sensors that adjust the nutrient needs of each plant. The most obvious way to cut water usage is to ensure every plant gets the amount it needs daily. Then, you use an underground system to catch excess drained water. It returns to the reservoir after you treat it to eliminate impurities and use in the following water cycle.

Use LED Lighting

There is no reason why commercial growers can’t use LED lighting instead of their HPS equivalent. First of all, it provides a better overall spectrum of light compared to its rivals. It doesn’t emit excess heat so that you can move plants closer. LEDs also don’t increase the temperature in the grow room as much. As a result, you don’t need your ventilation system to kick in.

LEDs are also approximately 60% more efficient than other systems. Did you know that the initial cost per photon of HIDs is at least five times higher than LED lighting?

Utilize Renewable Energy & Greenhouses

As you have learned, an indoor growing operation uses an extraordinary amount of energy. These days, there is an array of viable renewable energy options. You can use solar and wind power to account for at least some of your energy usage. A start-up called Scale Energy Solutions combines natural gas with solar energy. Its system could reduce its electricity bill by around 35%.

You can also enhance your artificial lighting with a little help from Mother Nature by using a greenhouse. Legislators need to provide rewards for growing cannabis in a greenhouse. One way to save energy is by using infrared polyethylene covers. They absorb and retain infrared energy. The result is a higher temperature in the greenhouse at night.

Best estimates suggest that a Columbian greenhouse is 370 times more efficient than an average indoor grow in Colorado! The main reason for the vast difference is Colorado’s reliance on energy from coal. If companies begin to trust wind and solar power, it will significantly reduce their carbon footprint.

Combined Heat & Power (CHP)

This is potentially another useful way to use less energy. It generates electricity and captures the heat that’s typically wasted. The result is the use of thermal energy, such as steam, for processes such as cooling, space heating, and domestic hot water. Already, many industries use CHP, which has a payback of 3-5 years. As a bonus, it doesn’t take long to set up.

Innovative Growing Techniques

For every company and individual that cultivates cannabis, enjoying large yields with low costs is imperative. One of the best ways to achieve this is by making the most out of your space. While the traditional method of growing horizontally will remain, there is potentially room for vertical cannabis growing.

The tactic involves stacking plants in rows upwards. After all, if you have a warehouse that’s 30 feet high, why not use it? Vertical growth is not perfect and has several issues. It comes with high start-up costs and safety and compliance problems. Nonetheless, it has the potential to increase yields while diminishing energy usage significantly.

A More Efficient Ventilation System

So far, the tips have helped potentially reduce energy usage from lighting. They have also reduced your grow room temperature, which means less air conditioning is required. The third member of the emissions triumvirate is the dehumidification system.

Many growers are unaware that traditional dehumidifiers release extra heat into the grow room. As a result, it causes the air conditioning to use more energy. You should look into a system that doesn’t release heat into the room. The best models could reduce energy usage by up to 65%!

Gather Data

In Illinois and Massachusetts, to name but two states, reporting energy use annually is a mandatory requirement. However, there remains a lack of data to outline how well energy efficiency in the marijuana industry is performing. We need to gather more information on water preservation, waste management, and plant physiology. Only then can we correctly assess the environmental impact of weed cultivation.

Final Thoughts on Growing Carbon Neutral Cannabis

In reality, the answer to the title question is likely ‘no.’ It seems incredibly unlikely that the marijuana industry will ever achieve carbon-neutral status. The demand for the herb has increased exponentially in recent years and is only going one way. As more states legalize the plant, there may come a time when the U.S. Government finally lifts the ban. If and when this happens, we expect dozens of countries to follow suit.

At that point, the industry will become so massive that carbon-neutral cannabis will surely become an impossibility. Unless there is a way to almost entirely rely on renewable energy, the carbon footprint from lighting alone will remain well above net zero. Then there is the small matter of the black market. We don’t expect illegal growers to follow best practices for the health of the environment!

What the legal industry can do is get as close to net-zero as it possibly can. This is possible through the use of technology to lower overall energy usage. New growing techniques can get the best out of space. Growers can also use different methods of reducing water usage. Overall, the marijuana industry may not see carbon neutrality, but it should work to become one of the lowest emitters of CO2. Perhaps a few operations will reach net-zero and share the secret of their success with others?

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