The Perils and Pressures of Growing Hemp Outdoors

Features - Feature

For outdoor hemp growers, climate change and nature’s unpredictability add to the challenges of growing the crop.

September 17, 2021

Courtesy of Iverson Family Farms

The nascent hemp industry has been full of surprises for growers, from production gluts to regulations that seem in constant flux. But for farmers who grow hemp outdoors, those unexpected obstacles come on top of nature’s uncertainties. With climate change, weather events and pressures are becoming increasingly magnified as wildfires, disease and record-breaking heat hit with force. But as hemp farmers face the perils of growing outdoors with resilience, they are discovering that so, too, does the crop they grow.

The Threat of Wildfire Ash and Smoke

As of Aug. 29, 85 large fires were burning in 10 states across the U.S., according to the National Interagency Fire Center. In many areas, 2021 has already set new records—this on the heels of 2020, the worst wildfire season in U.S. history, according to the New York Times. For hemp farmers under the far-reaching shadows of ash and smoke, wildfires add stress and dread. But thanks to new research, growers may rest a bit easier.

Courtesy of Iverson
Family Farms

As summer 2020 came to a close, wildfires burned within 10 miles of Oregon’s Iverson Family Farms (IFF). The third-generation multi-crop farm has grown hemp since 2016 as part of a vertically integrated operation that includes FSOil, a CO2 extraction company, on the same Willamette Valley property. The nearby fires transformed the fields into a Mars-like landscape of orange skies and falling ash.

While losing crops to fire was a threat for many hemp farmers, the smoke and ash impacted many more. As fires consumed homes along with trees and brush, potential contaminants blanketed sticky, trichome-covered hemp buds with ash and smoke.

For IFF and FSOil Director of Research and Development Giavanna Accurso, heavy metals were a significant concern. Ash often contains heavy metals, based on what’s being burned. “Hemp is a bioaccumulator, so it takes things up quickly,” she explains.

Skies were completely overcast for nearly two weeks, as the farm was under level 3 evacuation orders. The lack of sunlight hit hard. “Hemp is a photoperiod plant. It responds to the length of day in order for it to mature,” Accurso says. “Up until that point, the crops were doing fantastic. It was shaping up to be a great year for us.” But plant health began degrading and fungal pressures set in.

Courtesy of Canvast
Supply Co.

When Oregon State University’s (OSU’s) Global Hemp Innovation Center formed a Wildfire Smoke Effects on Hemp Stewardship Committee, Accurso was part of the group. Growers and researchers from Oregon, California and Washington met regularly to discuss the fires’ uncharted impact.

When a committee leader suggested wildfire effects might prevent hemp crops grown within 20 miles of the fires from meeting the requirements for export outside Oregon, Accurso didn’t accept that verdict.

“We kind of stepped up to that challenge and said, ‘Well, we don’t have the data for that yet, and what do we need to do to get to that point?’ So that’s when we started working with labs,” Accurso says.

As a vertically integrated company, the IFF/FSOil teams could trace and test flowers and extracted oil from pre-fire conditions, through the ash and smoke, and through harvests that followed once cleansing rains extinguished the flames.

“We pulled soil samples. We pulled samples during the fires. We pulled samples of plants with ash. We pulled samples after rains—three weeks down the line—and we had samples pulled from before the fire as well,” Accurso says.

But there was one catch: The methodology for testing hemp under these conditions didn’t exist. So, IFF and FSOil had to develop relationships with labs willing to develop the methods to test the samples and work alongside them in the name of research.

Testing measured pesticides and heavy metals, polycyclic aromatic hydrocarbons (or PAHs, a type of chemical produced when burned), smoke taint and potency. Samples varied by test but included ash, soil with ash, ash-covered flower, wet biomass with ash, oil from biomass with ash, and oil from biomass cleansed of visible ash by rains.

Accurso says she was shocked at how the rain washed the ash away. “It was undetectable visually,” she says. “After a couple of weeks of torture, it was a little bit of a sigh of relief to see that.”

The crop prevailed. Test results, outlined in more depth on FSOil’s website, yielded no concerns regarding pesticides or heavy metals for flower or oil. Full-panel PAH results were all below the limit of quantitation (LOQ) for all samples tested. Smoky or ashy taint was undetected. While potency on some varieties tested lower during the fires—possibly due to reduced photosynthesis—plants rebounded to similar or higher potency post-fire.

The Burdens of Southern Blight

As director of agriculture services for Tennessee-based hemp company Canvast Supply Co., Will Tarleton works with a hemp farmer network spanning everything from century farms to large commercial growers. A board member of the Hemp Alliance of Tennessee since 2014, Tarleton’s growing roots trace back to Humboldt County, Calif., and regenerative organic agriculture.

Tarleton notes many growers entering the hemp industry have never grown any crop. When unexpected weather or weather-fueled disease hits, these new growers often aren’t prepared for the hardships.

Southern blight is one disease in the spotlight for hemp growers in Tennessee and across much of the country. Research underway at Louisiana State University (LSU) aims to help growers nationwide overcome Southern blight and similar threats.

Courtesy of Dr. Raj Singh

Dr. Raj Singh, D.P.M., is director of the LSU AgCenter Plant Diagnostic Center. Known to his colleagues as the “plant doctor,” Singh works with hemp growers hard hit by Southern blight, a disease already well-known to Louisiana’s vegetable and ornamental growers. In 2020, the state’s first year for industrial hemp, Southern blight was the No. 1 problem hemp growers faced, Singh says.

Louisiana’s heat and humidity favor rapid development and spread of Sclerotium rolfsii, the fungal pathogen behind this soil-borne disease. But don’t be fooled by the name. “Southern” blight is found throughout the country. “It does persist in the northern climate, but the disease development is slower in those cases,” Singh says.

The Southern blight pathogen can infect hemp at any growth stage and persist in soil for years, Singh explains. Initial symptoms are yellow, wilting leaves. As the disease progresses, white fungal growth develops at the plant’s base, accompanied by small, tan sclerotia that mature to dark brown. Visible on topsoil, the fungus advances into the root zone and surrounding soil. Eventually, infected plants turn brown and die.

“The pathogen is very hard to control. It can only be preventatively managed to keep the inoculum lower or to keep the disease at low economic threshold,” Singh says. “But once you have those plants infected with the disease or with the pathogen in the field, then it is just a matter of time [regarding] how easy it’s going to spread to the nearby plants or maybe the entire field.”

Growers must be especially careful of the pathogen, Singh and Tarleton note. Southern blight spreads easily through infected transplants, infected soil, irrigation water, plant debris, tools, equipment—even boots.

Tarleton warns, “If I walk in someone’s field on their soil, and then come back to my farm with the same boots on and I walk in my field, I could potentially bring that pathogen back to my field.”

LSU researchers are screening hemp cultivars in hopes of identifying Southern blight-resistant varieties. Seed-grown plants are quarantined in the greenhouse to ensure they’re disease-free. Then, researchers inoculate the plants with Southern blight isolates collected from Louisiana fields in 2020 and wait to see if the disease appears.

“So far, we have close to 25 different cultivars that we have screened in the greenhouse. Unfortunately, all of them are susceptible to Southern blight isolates that we have here in Louisiana,” Singh says. He notes that some companies claim to offer Southern blight-resistant hemp cultivars. Singh hopes to add those cultivars and more to LSU’s research.

Courtesy of Global Hemp
Innovation Center

The Hazards of Heatwaves

In late June, unprecedented heat ravaged the Pacific Northwest. Hemp growers in the region reported triple-digit temperatures. Hundreds of deaths were linked to the heatwave, according to The Associated Press. In mid-August, soaring temperatures bathed hemp crops in excessive heat again.

Dr. Jeff Steiner, Ph.D., associate director at OSU’s Global Hemp Innovation Center, says plant establishment and sufficient soil moisture are key to surviving the heat. “Hemp is a very resilient plant. It’s very sturdy, but those types of temperatures for any crop are pretty stressful,” he says.

Steiner points out that temperatures above 100°F are beyond the optimal temperature for growth—even for heat-loving plants like hemp. The plant’s establishment and growth stage factor into its resilience against heat, potentially influencing flowering, flower maturation, and secondary metabolites such as terpenes and cannabinoids.

Iverson Family Farms’ hemp field during the 2020 wildfires
Courtesy of Iverson Family Farms

Steiner says growers who transplant may have a jump on those direct seeding, but much still depends on site-specific conditions at planting time. “If folks are tied into having to plant at a certain time and the weather is just very, very hot and dry, that can cause stress for the plants.” He adds adequate soil moisture helps offset stress.

OSU researchers did some replanting this year after hemp plants failed. Steiner says some California colleagues had to do the same. But he’s not inclined to blame the heatwave alone, saying weather, seed quality, method and timing of establishment all play a role. “It’s a very complex issue,” he says.

Temperatures at IFF hit 113°F during June’s peak heat, Accurso says. Some transplanting was delayed, but Accurso says the late crop looks good. “I feel like we’re pretty lucky at the moment that we’re working with a plant that does appreciate the heat,” she says.

Worker safety—already a priority for IFF—took on added emphasis as field workers faced the heat in 35 acres of hemp. IFF does some mechanical cultivation, but a lot of the weeding is done by hand.

“With our workers, we start the day early. We have shaded mobile areas for them, and then we try to finish earlier,” Accurso says.

While many area crops suffered, Accurso says the hemp wasn’t hurt. “A lot of crops will stunt and stop growing at heat that high. With hemp, we don’t really see that. Hemp loves the heat,” she says. “We have not seen stunting with any of the plants. They all look great. Everything is still green.”

Accurso says IFF’s judicious water use has kept them within their water rights. But growers in other parts of the state aren’t as fortunate. “When you get up into the high desert, the water rights become a lot more challenging. So, a lot of those growers are having to cut off their irrigation to their crops before the [normal] time,” she says.

IFF's irrigation methods vary by field, but Accurso underscores the benefits of drip irrigation, which goes straight to the plant. Some Pacific Northwest growers reported that late-June temperatures were so hot that overhead watering evaporated before it reached the ground.

Steiner suggests the unpredictability of outdoor hemp cultivation is compounded when hemp is grown in areas not optimal for the crop. “We still have to get a handle as a U.S. industry on the best places to grow hemp. People grow hemp where they grow it because they’re excited to grow hemp. But how does that pan out economically?” he asks.

For new outdoor hemp growers, Tarleton offers advice: “Talk to the old-timers. They have a pretty good idea of the rhythms and cycles of your area. … Start small, and remember this is agriculture. Hemp is a crop, and there can be crop failure.”

He adds, “You have to be out there in your field every day. It’s dirty boots for the whole season. But keep your boots clean.”

Jolene Hansen is a freelance writer specializing in the hemp, horticulture and specialty ag industries. Reach her at