Hemp Cross-Pollination Could Damage Cannabis Crops—Here’s How to Prevent It

Published on July 17, 2019 · Last updated July 28, 2020
(кирилл поляшенко, gameover2012, ilbusca/iStock)

Since the 2018 Farm Bill passed, hemp production has increased across the country—from 25,713 acres in 2017 to 78,176 acres in 2018—according to a crop report from Washington-based Vote Hemp.

While that’s exciting news, this surge in hemp cultivation has caused worries among marijuana growers about cross-pollination, a natural process that can reduce the potency of a female plant’s cannabinoids.

How have policymakers and regulators addressed this problem? With a few exceptions, not at all, or with great hesitancy. Figuring out what’s happening and who’ll take care of this issue has caused paralysis in many states.

Is Legal Hemp About to Ruin America’s Outdoor Cannabis Crops?

Dr. Heather Darby, who leads the University of Vermont (UVM) Extension Northwest Crops and Soils Program, says: “A lot of things have happened so quickly there hasn’t necessarily been details figured out. Up until December 2018, there were a lot of restrictions on hemp, but now there’s so many more people starting to grow, new concerns are popping up.”

What Is Cross-Pollination?

Cannabis is a dioecious plant, meaning that male and female features occur on different plants instead of the same one. Female marijuana plants produce flowers which farmers grow for their cannabinoid content and people smoke to get high, but if male hemp plants—which are needed for fiber and seed—are planted too close, the hemp can pollinate the cannabis females. That can cause the cannabis to seed out, lessening yields, cannabinoid content, and potency of the stuff you smoke.

Almost all of the hemp grown in the US today is for CBD oil, according to Darby. The males are only necessary when growing industrial hemp for fiber and seed and those products fetch a much lower price. However, Darby believes that will change as the price of CBD drops and fiber-processing equipment in the US becomes available.

Nevertheless, even during this CBD-dominant market, cross-pollination is a risk. Large outdoor hemp fields, even grown with feminized seeds, will still have a few rogue male plants. Grown at scale, it’s impossible to guarantee 100% female germination.

Policies and Regulations

It may be lawsuits that force the issue because policy has been mostly reactive when it is made. There have been a few cases of lawsuits in the millions of dollars due to pollen contamination, most famously by Oregon CBD.

“Most lawmakers are ignorant of the hemp industry in general, let alone a nuanced situation such as this,” says Rye Matthews, Chief Technology Officer at Northeast Hemp Commodities. “States don’t seem concerned. They’re letting farmers do as they wish and expecting that the market and private disputes will work themselves out.”

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Besides being nascent industries, hemp and marijuana are usually regulated by different agencies: The Department of Agriculture for hemp, and for marijuana, either an agency specific to it or the Department of Health. This means people often don’t know which agency to approach and agencies don’t want to step on each other’s toes.

States With Policies

Some states have been proactive in trying to prevent hemp cross-pollination with cannabis crops.


Both state government and municipalities want to shift responsibility to the other in Arizona, but commercial growers have picked up the slack. In August 2018, Snowflake, AZ, passed an isolation ordinance to protect a large marijuana grow run by Copperstate Farms. At least two other companies are now looking for similar treatment in other municipalities.


More than a dozen counties in California have enacted temporary moratoriums on hemp cultivation due to concerns by marijuana growers. Sonoma County, for example, may allow indoor production of hemp, or limit cultivation to specific feminized seed varieties. Some hemp activists complain that counties are flouting state law.


While Colorado is second to Montana in hemp acreage as of 2018, it’s the leader of hemp production in the US. That also makes it the most vulnerable to cross-pollination. In Pueblo County in 2017, pollen drift caused a marijuana crop loss of 12 to 18 percent. They enacted a four-mile isolation area between industrial hemp and marijuana grows, but it has been judged ineffective.

According to “Wild” Bill Billings of the Colorado Hemp Project, the worry is valid. “The whole state’s in trouble,” he says, and Pueblo’s solution, which may become state law soon, is not enough in areas like the South East and the Western slope.


In the Willamette Valley in particular, if you want to grow seed, you have to choose land that’s five or more miles away from already registered cannabis growers. There are some ongoing court cases because pollen contamination has already happened. The state already institutes isolation requirements for sugar and table beets, so applying that to cannabis and hemp wouldn’t be a new process.

Does the Farm Bill Legalize CBD, Too? Not Exactly


The state’s pilot program initially required four-mile isolation between hemp and marijuana fields. With some 1,100 licensed marijuana growers in Washington and hemp’s requirements for large tracts of land, location has become a major challenge.

A new bill this year removes isolation but allows the state’s Department of Agriculture to consider evidence of cross-pollination and take action if needed. Established growers have priority.

Cross-Pollination Prevention Methods

There are a few ways to prevent cross-pollination between hemp and marijuana.


Cull the males by monitoring plants and pulling out “escapes” as soon as they’re spotted. Matthews from Northeast Hemp Commodities advises to be vigilant with hermaphroditic plants. “Even with fem seed or clones you’ll get some hermies if you’re growing more than an acre or two.”

Male plants tend to produce pollen sacs a week to ten days before female flowers begin to bud if planted at the same time.

Communicate With Neighbors

Keep tabs on the flowering times of plants nearby. Some agricultural county offices have pin maps where farmers can update where and what they are growing and can keep tabs on neighboring farms.

Stagger Planting

By planting industrial hemp and feminized cannabis crops at different times, they will also mature at different times. Caution: Predicting flowering and pollen release is an inexact science.

Enforce Isolation or a Buffer Zone

Pollen can travel up to 30 miles, but 3-15 is the most common range.

Purchase Feminized Seeds

If that’s not possible, use gender detection screening tools.

Surround Cannabis Plants With Different, Taller Plants

These can block pollen. Matthews recommends thick windbreaks such as Norway Spruce.

HEPA (High Efficiency Particulate Air) Filters

For indoor grows and greenhouses.

When this industry gets into a groove and implications of cross-pollination become clearer, broader policies will likely form. However, vigilance on a local level will always be required, especially when industrial hemp expands in the coming years.

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Christine Giraud
Christine Giraud
Christine Giraud, a freelance writer in Boston, has been writing about cannabis for publications like The Boston Globe, Overture Global Magazine, Dig Boston, Civilized, Her(b) Life, and Foottraffik.
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