OSU Extension’s hemp harvest-timing research helps growers stay legal and protect profits

Hemp has the potential to become a major agricultural commodity in Oregon and the United States, with hemp plant fiber being used in manufactured products, including clothing, construction materials and packaging. Meanwhile, hemp seed oil is being investigated for use in pharmaceuticals, cosmetics, foods and nutraceuticals.

Selecting the appropriate harvest date is an essential tool for growing successful crops, but the cues for hemp haven’t been developed. If hemp is harvested at an inappropriate time, it could exceed the legal limit for THC (tetrahydrocannabinol) – the regulated psychoactive compound found in marijuana – and as a result the hemp couldn’t be sold as a crop.

In response to industry concern, Gordon Jones, Oregon State University Extension agriculture faculty in Jackson and Josephine counties, conducted a harvest-time study at the Southern Oregon Research and Extension Center in Central Point. Hemp flower samples were collected each week from four varieties from August to late October 2020 and sent to a U.S. Department of Agriculture lab for cannabinoid analysis. In 2021, Jones repeated the study at K-Bar Ranch, which is owned and operated by the Cow Creek Band of Umpqua Tribe of Indians, in the first Extension collaboration of this type with the tribe.

As a result, the preliminary results of Jones’s study were appreciated at the Southern Oregon Hemp Growers Forum and the Klamath Basin Hemp Field Day in 2021. One grower, whose 10-acre hemp crop had a conservative value of $50,000-$75,000, wrote, “The timing of your presentation on CBD content was perfect as it gave me the belief to hang on in there, and our crop finally went up from 3% to 9.7%. I was happy with the result. Without your presentation I would have probably bailed out and written the crop off!”

The work was funded by the OSU Global Hemp Innovation Center and the Agricultural Research Service, the principal research agency of the U.S. Department of Agriculture.

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