Photo by Dr. Jessica Lubell-Brand
Left plant: A triploid shoot without seed formation; right plant: a diploid shoot with seeds developing. UConn researchers pollinated each plant in the greenhouse with male pollen to test for sterility.


The year was 2016. Cannabinoid hemp breeder Oregon CBD tried to produce feminized seed, but it found its crop had been pollinated—and not with the pollen it had planned on using. So, Oregon CBD’s parent company, Jack Hempicine, sued a nearby grower for cross-pollinating and ruining the crop with pollen from cannabis plants high in tetrahydrocannabinol (THC).

Dr. Seth Crawford, Ph.D., co-founder of Oregon CBD, claims the defendant's cannabis also pollinated other plants as far as 35 miles away. The suit was an attempt to set a legal precedent for cross-pollination issues between cannabis and hemp farms in Oregon. But proving the pollen came from that grower was difficult to do in court, and Oregon CBD ultimately abandoned the legal battle.

“In this case, there were claims that it could have come from any other farm,” Crawford says. “We had pretty good evidence that it was not coming from other farms; it was coming from this particular point source. But it’s different to scientifically know something versus to be able to prove something in a court of law.”

Along with tumbling prices and unsold biomass, add cross-pollination to the pile of challenges stacked against hemp growers.

What’s Happening With Pollen

Male hemp crops in grain or fiber plantings can pollinate female hemp plants grown for compounds such as the cannabinoids cannabidiol (CBD) and cannabigerol (CBG). They can also pollinate female sinsemilla, or seedless, cannabis plants, which are also grown for compounds such as the cannabinoid THC. The result is often unwanted seed development that can reduce resin (and therefore cannabinoid production), as the plant kicks into a reproductive stage that many cannabis and hemp flower growers take care to avoid.

Oregon CBD’s situation was a variation on that theme. The aim was to produce seed, after all, but the company suspected the seed, once the plant was pollinated from the neighboring farm, wouldn’t have the characteristics it was looking for. Crawford says of outside pollen drifting into Oregon CBD’s feminized seed production: “The important thing to recognize with this is that the plants themselves are not genetically impacted by pollination. … But any of the resulting seeds that came off of the plants in the field would then be non-compliant.”

Pollination between cannabis and hemp has also spurred legal action in Colorado. Nadav Aschner, partner at The Rodman Law Group, defended an outdoor hemp grower there in a lawsuit in which a nearby cannabis grower accused the defendant of cross-pollinating its cannabis crop.

Aschner and his client countersued for negligence and abuse of process, claiming, he says, that the cannabis grower improperly sought a preliminary injunction against Aschner’s client to prohibit the client "from cultivating hemp at its property.” He says the cannabis grower’s “pleadings ... failed to appropriately reflect the science of cannabis cultivation and plant biology, ... misrepresenting the risk of ‘imminent and irreparable harm’ that could be caused by Aschner’s client’s hemp crop.” The cannabis grower provided the hemp grower with a settlement, though the settlement amount is confidential.

The conclusion of the dispute underscores, again, the difficulty of proving cross-pollination in court. Discussing cross-pollination woes more generally, Aschner says, “It’s really, really, really hard to prove that it was from this crop and not the one next door, or the one a mile away, or the one 12 miles away on a breezy day that ended up causing the cross-pollination.”

However, pollination doesn’t always cross property lines. Growers can unintentionally pollinate their own crops, says Robert C. Clarke, co-founder and consultant of the BioAgronomics Group and a Hemp Grower editorial advisory board member. “People point fingers and blame very easily, but a lot of times, people should look at home first,” he says.

In cannabis production, a small fraction of seeds or clones marketed and sold as sinsemilla can turn out to be male, says Clarke. Cannabis plants can also develop intersex, also known as hermaphrodite, characteristics. And as with males, Clarke says it doesn’t take much pollen for one intersex plant to ruin a cannabis grow.

The same issues happen in hemp cannabinoid production, where the breeding lines are less developed, Clarke says. “A lot of people have been caught up with buying bad seed for many reasons—[the seeds are] non-productive—and other reasons just besides making a few male flowers,” he says.

Many growers have entered the hemp and cannabis spaces after working with other crops, Aschner says, and they think they know what they’re doing. In reality, their experience doesn’t always directly translate.

“If everyone knew how to grow hemp really, really well, and marijuana really, really well, and everyone knew to look for the male plants at a certain time after germination or seeding—whatever you’re doing to propagate your crop, … there would be less cross-pollination,” he says.

Site Selection

As the distance between cannabis and hemp crops increases, the amount of pollen that wind carries between them decreases, says Clarke, an ethnobotanist, plant breeder and agronomist who authored “Cannabis: Evolution and Ethnobotany,” among numerous other books and articles.

In one study, researchers from Agriculture and Agri-Food Canada (AAFC) / Eastern Cereal and Oilseed Research Centre stated that high-quality hemp plants in Canada and Europe must have a 5-kilometer (3.1-mile) distance between them to avoid unfavorable pollination.

Oregon CBD cultivars at a farm in Southern Oregon
Photo courtesy of Oregon CBD

The AAFC researchers also noted that wind directions influence pollen travel. “The amount of pollen distributed downwind was about six times the amount distributed upwind,” the study states. In effect, being isolated by 0.9 km upwind would be the same level of “isolation” as being 5 km downwind, per the study.

The size of farms and the distances between them influence pollination rates. “If you’re in Kansas and you’ve got large distances between farms, because everyone’s properties are pretty massive out there for farming, there’s probably a little bit less of a likelihood of cross-pollination,” Aschner says.

Growers cultivating in controlled environments might be afforded some protection for their crops and those of nearby cultivators. In a cross-pollination sense, greenhouses are better than outdoors, Clarke says, but may not offer significant protection, especially if they are not sealed. Indoor growers with filtered intake ducts should not have cross-pollination issues, he adds.

Once cannabis is federally legalized in the U.S., Clarke predicts, agricultural extension offices will be able to advise growers on which crops work in which regions, both from an economic standpoint and to let them know the locations of other nearby growers who could produce or receive problematic pollen.

In their Hemp Grower column “How Seeded and Seedless Hemp Crops Vary for Different End Uses,” Clarke and BioAgronomics Group co-founder Mojave Richmond wrote that they anticipate hempseed and hemp fiber cultivators will grow in areas where broadacre agriculture is already widespread. They also note that sinsemilla growers have established themselves in other areas, such as rural pockets in Northern California.

“Across North America,” they wrote, “effective and fair regulation of our burgeoning cannabis industry will largely rely on understanding which branch of our industry was established in each region first, and whether a precedent exists for its continuation.”

Growers of pollen-producing hemp should be at least 10 miles from sinsemilla growers if possible, Clarke and Richmond wrote, adding, “Safe distances should be increased to up to 30 miles or more if the pollen source is a broadacre grain seed field or if seedless crops are established downwind of seeded crops.”

The Triploid Option

At Oregon CBD, the company decided to not only attempt setting a legal precedent on cross-pollination, but also introduce a scientific remedy. Participating in research trials at North Carolina State University, Cornell University and the University of Kentucky, Crawford and his team are working to create sterile, triploid hemp crops with three sets of chromosomes.

To create the triploids, the researchers crossed hemp with two chromosomes, which are naturally occurring and called diploids, with tetraploid hemp that they had created with four chromosomes.

Crawford says that “triploids are, for all intents and purposes, sterile. You can get one or two seeds if you have intense pollination happening, but these are essentially sterile plants.”

As for the tetraploids, Crawford says, “Tetraploids can make seed with diploids pollinating them. They can make some seed [when they pollinate other] tetraploids but not nearly as many. And then diploids being pollinated by tetraploids—they set seed, but they’re not viable seed—there are no embryos.”

University of Connecticut (UConn) researchers have also created triploid genetics by crossing diploids with lab-created tetraploids. They published their findings in the September 2020 HortScience paper “Production of Tetraploid and Triploid Hemp.”

“You don’t get viable eggs in triploids, and therefore, if there are no viable eggs, they can’t be fertilized by pollen and set seed,” says Dr. Jessica Lubell-Brand, Ph.D., an associate professor at UConn who worked on the study.

Seedless watermelons sold at the supermarket are triploids bred by plant breeders in a similar way, Lubell-Brand says—by doubling the chromosomes of a diploid to make a tetraploid, then crossing that tetraploid with another diploid to make a triploid. “It’s the triploid seed that the farmer grows, which is seedless, and that gets to market. Same thing with triploid citrus, triploid hops and other common [crops],” Lubell-Brand says. “Sometimes you might get a tetraploid from the wild that you could use, but with most of the food crops, it’s been done by plant breeders.”

The UConn researchers wrote in “Production of Tetraploid and Triploid Hemp” that triploid hops produce higher yields and have more alpha acids than diploid hops. Triploid hemp might also have benefits beyond sterility, they stated, writing, “It is possible that triploid hemp may offer some unique cannabinoid profiles or increased secondary metabolite content.”

Photo courtesy of Oregon CBD

Crawford says he has seen a slight, non-statistically significant cannabinoid content increase with Oregon CBD’s triploid genetics compared to its diploids. He adds that in hemp with higher ploidy levels—triploids, tetraploids and above—there appear to be more “olfactory compounds,” such as terpenes and aldehydes.

To follow its HortScience paper, UConn received a U.S. Department of Agriculture grant through the Sustainable Agriculture Research & Education program. Lubell-Brand will use those funds to lead a project to explore triploid hemp sterility, plant performance and cannabinoid production in field and greenhouse settings.

Triploid hemp could prove beneficial, Lubell-Brand says. “I think it’s going to be a nice option, whether it has enhanced metabolites or not,” she says. “As long as they’re not reduced, I think it could be a good option for farmers.”

Post-Pollination Remedies

If growing triploid genetics and distancing crops prove unrealistic or unsuccessful, growers may have a few options if their crop gets unintentionally seeded.

Many hemp growers focused on CBD production extract the CBD after growing rather than selling smokable flower, Clarke says. They’re more focused on the extract, or “goop,” than flower quality, he says.

Seed production at Oregon CBD
Photo courtesy of Oregon CBD

Those growers may see a silver lining in a cross-pollination event, as long as there aren’t too many seeds. “They should, even with a few seeds in there, get plenty of goop,” Clarke says. “It shouldn’t really interfere with anything, as long as you’re not trying to put a bunch of seeds through the extractor, which are oily and have other problems.”

If growers' crops have an abundance of seed, Clarke says, “They better have a use for the seed.” Growers can eat them or feed them to their chickens if they have any, he says.

When it comes to selling seed that has set on cross-pollinated plants, University of Illinois Extension Commercial Agriculture educator Phillip Alberti says he thinks there’s potential behind selling the grain for processing into food.

“We don’t have enough information to definitively state that it will [work],” Alberti says, considering unexpectedly pollinated plants have different characteristics than grain-type cultivars that are bred and grown for food production. “...[Y]ou just don’t know how [the seeds] are going to perform, and I think at that point, quality will be a bigger indicator."

He adds that seed size, oil content and processor specs would all affect the marketability of the seed.

There’s also the issue of sticking to an existing contract or agreement, timing production—as grain crops usually flower before cannabinoid cultivars—and finding a buyer, Alberti says. In the Midwest, farmers have a “tremendous amount of interest” in grain production, but meanwhile, he says, “there really isn’t too much of a grain market,” in part because of a lack of processing facilities.

Similarly, there may be hope, though challenges would exist, for cannabinoid growers whose crops get cross-pollinated and who are considering selling stalk components. Cannabinoid producers generally grow cultivars with a thick hurd, or woody inner core, compared to those generally used for fiber, Alberti says. “If one could separate the fiber from the hurd, I think the hurd would more likely be a potential profit generator,” he says.

“Growing hemp for grain and fiber I’m not going to say is a 100% fit for everybody,” Alberti says, “but it’s more attuned to what we know how to do [in the Midwest], which is hay forages and grain [from] corn.”

A Resonating Message

An increase in hemp and cannabis production could provide more medicines and materials—such as hempcrete, animal bedding and packaging—to people, sequester carbon and create new jobs, among other benefits. As those realities come to pass, multiple sources featured in this article say growers will need to respect each other’s production, including with regard to pollination.

“I think as the industry expands, people should be very careful to be good neighbors,” Clarke says. “And I think that lesson applies to anything in life, actually: Be considerate, be respectful, be a good neighbor.”

Patrick Williams is the managing editor for Hemp Grower magazine.