What Was Once a Weed Could Fuel Jet Engines

Could growing weeds help the planet?

Field pennycress, a plant in the Brassica family related to mustards and cabbages, is usually considered a weed. But one feature made it less of a wallflower: its very high oil content, about 50% higher than that of a soybean. After close to a decade of controlled breeding and gene-splicing, the onetime weed is being cultivated as a source for renewable diesel or sustainable aviation fuel.

Most biofuels in the U.S. currently come from corn or soybeans. But as demand for green fuels rises, global food shortages are also threatening. That’s bringing a push for low-carbon fuels that can be made without using edible grains—and spurring research on crops like field pennycress. 

“Today the dominant feedstock oil source for [biofuels] would be soybeans, which creates this dynamic of, ‘Are we going to be using our soybean oil and our soybean meal for the fuel market vs. the food and feed markets?” says Mike DeCamp, the chief executive of CoverCress, the company that developed field pennycress. The plant, now also dubbed CoverCress, is aimed for cultivation on farms in harvest offseasons, as a so-called cover crop that can help prevent erosion and provide revenue when primary crops are fallow.

CoverCress is one of three nonfood cover crops that have received funding from the U.S. Department of Agriculture, where scientists have been hoping to find oilseed plants that could potentially produce renewable fuels without competing with food sources. The other two—Nuseed Carinata and a plant called camelina marketed by Global Clean Energy Holdings —are also oilseed crops that are grown during the winter fallow period.

Major oil companies have been getting on board. In 2022, BP agreed to buy Nuseeed Carinata oil to process or sell as a supply of sustainable biofuels. Chemical and pharmaceutical giant Bayer expanded its stake in CoverCress to a 65% ownership share, with the remainder held by Chevron and agricultural trading house Bunge. Exxon Mobil has a multiyear agreement with Global Clean Energy Holdings to purchase renewable diesel made from camelina. 

Growing these oilseed plants between main crop rotations on land already used for farming helps limit damage like deforestation, says Alex Clayton, global strategy and commercial lead for Nuseed Carinata.

Carinata, also known as Ethiopian Mustard, isn’t a weed like pennycress but also isn’t edible by humans. The crop, grown between November and May in the offseason for cotton and peanuts, is being tested by farmers in Alabama, Georgia and Florida, as well as in Argentina. The oilseed is crushed in Europe for use as a biofuel. 

The companies behind these crops tout benefits to farmers, but convincing farmers to grow them can be a major hurdle. 

“Farmers are very cautious, conservative and skeptical because they have heard a lot of promises that haven’t panned out,” says John Sedbrook, a professor of genetics at Illinois State University who is researching cover crops. “It has a lot of potential but there is a lot of work to be done.” 

In most cases, farmers are contracted to grow the crops, with the companies determining when and how to use fertilizers as well as ensuring the plants are crushed and sent to the refiners. That loss of control, as well as overlaps of up to a month with cash crops that can delay planting can make these cover crops a tough sell.

How the crops have been developed also can be an issue. In the U.S. growing GMO crops is legal, though regulated by groups like the U.S. Food and Drug Administration and the U.S. Environmental Protection Agency. However GMO crops are largely banned in the EU, which is a limitation for CoverCress. By contrast, Nuseed Carinata and camelina were developed mainly through selective breeding, rather than genetic modification.

Aviation is among the industries that are pushing demand for biofuels like those produced with cover crops. Sustainable aircraft fuel, or SAF, is still very much in its infancy. Output in 2021 was 100 million liters but in order for the industry to achieve net zero carbon output by 2050, around 449 billion liters will be needed, according to the Montreal-based International Air Transport Association. In 2022, 450,000 flights used SAF as a fuel source, the IATA estimates—just 1.5% of the flights that took place. 

“We don’t have the solutions at scale today to actually solve the problem of decarbonizing how we fly,” says Lauren Riley, chief sustainability officer at United Airlines Holdings.

“If you think about some other markets, like ground transportation, they’re electrifying. They have batteries that are becoming more efficient and energy-dense with each generation. We don’t have sort of the equivalent of that for aviation.” 

The new nonfood sources of biofuels are promising, she says. “Cover crops have the potential to take us to almost a carbon-neutral fuel which is exceptionally exciting.”

However, cover crops can only supply so much, says Hemant Mistry, director of energy transition at the International Air Transport Association. “A diversity [of sources] will be needed to ramp up SAF production going forward.” 

“CoverCress, camelina and Carinata combined are not going to be the solution [alone],” says CoverCress CEO DeCamp. “It’s still not going to be enough oil to meet the demand based on the amount of capacity that’s coming online.”

“None of these crops are the magic bullet,” he says, “but they are part of a fabric that can really help in long-term lowering greenhouse gas emissions in the world.” 

Write to Yusuf Khan at [email protected]