The Secret Pot-Growing Operations in America's Cornfields

The same tech that’s helping farmers with legal crops is a boon to the agricultural underworld.

Gary Cameron/Reuters

On any given weekday in the summer, you will find me walking through fields counting bugs. In fact, it’s my job: I’m an ecologist studying the communities of insects that live in agricultural landscapes. Most days between early June and early September I drive between farms to scout crop pests and the beneficial insects that eat them, changing sticky yellow glue traps and sweeping vegetation with a canvas net.

But a single afternoon in August 2006 stands out in memory. Along one of the transects my colleague and I had set up in a cornfield, we noticed that several plants around one of our traps were missing.  Strong winds or hail can knock down whole corn plants but what made this remarkable was what stood in their place: marijuana. Specifically, there were five plants, each standing about eight feet tall, in the middle of our survey plot and bursting with buds ready to harvest. While we were deciding how to proceed and what to tell the landowners, we received our next surprise; someone else was rustling through the field towards us.

It’s rare to happen upon someone strolling through a cornfield—and for good reason. If you’ve never walked through one, it is not a pleasant experience. Tightly packed rows of stalks almost 10 feet tall create an almost full canopy overhead. Underneath, row widths much narrower than your hips include sharp, jutting corn-leaf edges that inflict papercut-like nicks to any exposed skin as you brush past. And if you’re there during the tasseling and silking stages, your skin may break out in a rash from the falling pollen. Appropriate attire for field scientists in cornfields includes boots, long pants, and sleeves, a sturdy hat, and glasses to protect your eyes from being cut by the leaves. In other words, anyone making the trek into a cornfield is going with purpose, whether to sample insects or surreptitiously grow marijuana.

When the person approaching saw us, our field gear, and our surprise, they quickly disappeared back into the dense sea of green stalks. While we never saw them (or their marijuana) again, it became clear that this was not an isolated incident. Almost every corn grower I spoke to that summer had a tale of discovering marijuana in their cornfields at harvest time. Which led me to ask: What is it about the nation’s largest crop that has made it so attractive to marijuana growers in recent years?

The answer: Growing marijuana has become possible and desirable, not to mention nearly untraceable, thanks to the very innovations that created industrial-scale, precision agriculture in the first place.

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In an arms race to grow more food for a ballooning world population while still turning a profit, commodity farmers are turning to quantification. By carefully monitoring their inputs and outputs, growers turn usage information into optimized and personalized plans for each of their fields.  They map their field perimeters using GPS technology. They plant crops in laser-fine straight lines while streaming Netflix over wifi in their air-conditioned tractors, which count the seeds planted in real time. They precisely apply pesticides with helicopters, which are safer and more effective than crop dusters, reducing the amount of chemical needed. At the end of the growing season, they measure crop yield on a plant-by-plant basis as the combine harvests, revealing within-field patterns of variability never known before. Recently, agribusiness corporations have even proposed tracking that yield data at continental scales during harvest, which would be used to alter grain market prices into the next year. And while the Federal Aviation Administration has not yet legalized the use of drones for commercial purposes in agriculture, researchers have already started flying them over fields to record plant health and track pests, disease outbreaks, nutrient deficiencies, and drought stress at landscape scales.

All of this is possible without a corn farmer needing to step foot into the field, which is remarkable—and critical for several reasons. First, over half of American commodity farmers now call farming their secondary occupation, according to the most recent national agricultural census. And who has time to walk through a field when you have another full-time job? Second, commodity corn pricing forces growers to focus solely on the bottom line. They’re working to produce as much as possible, which lowers prices if everyone has a good year, while hoping for high selling prices, which depends on other growers having a poor year. (Harvesting 1 bushel, or roughly 70 pounds, of grain corn would get you $3.77 on the Chicago Board of Trade this winter.) Third, more and more agricultural land is being turned over to corn. In large part this is due to the push for corn as a biofuel feedstock. Lastly, the land cultivated by individual farms is increasing. Also according to the latest census, the average farm size is 434 acres — with over 336 million acres of land held by farms that are 5,000 acres or larger. This has led to amazing productivity in our country—America is the world’s leading producer of corn, harvesting nearly 376 million tons of it in 2012. How can a grower walk through all that land?

The truth is that they don’t.

Once a corn field is planted and herbicide applied, many farmers don’t return to a given field until harvest time. The biotechnological and labor-saving innovations that have reduced costs for corn farmers mean that literally no one walks into the average corn field during the growing season. Which presents a major opportunity for marijuana growers. Indeed, entire Internet forums devoted to sharing tips for growing marijuana in other people’s corn fields have sprouted.

In earlier years, marijuana growers who wanted to illegally grow on others’ land often sought out large swaths of remote natural areas. But law enforcement technology caught up, using helicopters outfitted to detect these large areas of marijuana within forest or other vegetation by thermal imaging.  The Forest Service has estimated that the majority of their law enforcement division’s workload is spent on investigating illegal marijuana growing on their lands. In Wisconsin alone, there were nine busts of large-scale marijuana growing operations between 2008 and 2012 on state, tribal, and national forest lands, resulting in the removal of over 45,800 plants, according to Wisconsin Department of Justice data compiled and reported by the Milwaukee Journal Sentinel. At an estimated retail value of $2,500 a pound, that’s over $114 million.

Growing marijuana in cornfields keeps it better hidden than growing in remote forests, albeit in plain sight. Helicopters and thermal imaging are only able to detect large patches of marijuana by color difference. So marijuana growers use GIS technology and handheld GPS devices to spread out their growing into distributed networks of small patches, like the one I stumbled across. This tactic also reduces the risk of losing one’s marijuana crop: If one patch is found and destroyed, the rest of the plants are in other locations, known only to the GPS and the marijuana grower. Man-made patterns in natural areas are a telltale sign of marijuana to enforcement agencies; growing it in corn renders that giveaway moot, as everything is in rows. The growing conditions for marijuana are also better in cornfields than remote forested land: Every input that corn farmers carefully measure and apply to maximize their crop growth—fertilizer, herbicide, irrigation—benefits the marijuana plants, too.  Forests and hillsides formerly chosen for their camouflage of illegal marijuana were barriers to sunlight, whereas cornfields are often in full sun.  Additionally, some forest evergreens acidify the soil around them, potentially inhibiting marijuana growth. Arguably most importantly, marijuana can be transplanted into a field after corn is planted and grow to maturity before the corn is harvested. Which means corn farmers often don’t even know they had marijuana in their field until they’re sitting atop the combine in September.

This agricultural underworld is likely all across the Corn Belt of the United States, and has been for decades, as highlighted in Dr. Ralph Weisheit’s 1992 book, Domestic Marijuana: A Neglected Industry.  Yet it never appears in the numeric representations of corn growing, like the agricultural census. Nor does it appear in life cycle analyses, such as “King Corn,” the popular 2007 documentary attempt to demonstrate the seed to table journey of corn in the U.S. (While those filmmakers found hemp growing in their field, it was of the industrial rope variety.)  As Lieutenant Jason Freedman of the Dane County Narcotics Task Force recently told me: “It is occurring all over the county. Even though they are small operations and subject to weather, outdoor growers are the primary source of local production. That was not the case 10 years ago.”  Elyse Schaffer, the public information officer for the Dane County Sheriff's office, confirmed: “We definitely find those grows on a regular basis.”

All the corn farmers I’ve spoken with who have found marijuana in their fields report it to the local authorities, even though traditional reporting of drug crimes and arrests don’t capture this reality. While the DEA reports that it eradicated over 4 million marijuana plants cultivated outdoors in 2013, it would take a formal Freedom of Information Act request for even the chance to find out how often or where these growing incidents occur in corn.  Lieutenant Freedman estimated that “less than 10%” of the marijuana his group seized in the past few years has come from corn fields. He acknowledged that marijuana grows in corn fields don’t appear in reports like annual records of confiscations and arrests in large part because they are rarely discovered and even more rarely result in an arrest: “They are anonymous and hiding in plain sight; law enforcement is much less likely to come across them [than indoor growing operations.] A very small percentage of outdoor grows lead to an arrest. Has it happened? Yes, but single digits.”

The farmers I work with here in Wisconsin, where corn is worth $2.2 billion a year, seem both annoyed and bemused by this trend. The average farmer is growing food on 195 acres; some of them have thousands. One family I work with is a third-generation farm growing on 2,000 acres—over half of which are corn. The past several years they have found marijuana growing in at least one of their fields during harvest and reported it to the police. (The family asked not to be identified in this article, citing privacy concerns.) Sometimes they catch it before the growers harvest the marijuana, other times not. In 2010, they found an unusually large patch, two rows of 400 plants along a field edge that had yet to be harvested. The local cops staked it out overnight but the marijuana growers never showed. The DEA was called in to cut down and burn the contraband. Knowing the time, energy, and money that go into a crop, the family cursed the idea that someone was freeloading on their good soil and irrigation.

As they watched the bonfire die down, they asked the DEA officials to estimate the value of the marijuana they had just burned. The reply: half a million dollars. The farmers had to laugh. The value of the corn that had been cut down to grow it? $32. Piggybacking on the incredible technological investments required to create so much corn, marijuana growers reap orders of magnitude more revenue per acre. This fact is not lost on individual farmers, but is virtually undetectable in national conversations about the profits and pitfalls of industrial corn agriculture.