Hemp grown on an eastern Idaho research plot shows good herbicide tolerance.

“There were a few herbicides we applied that I was surprised the hemp was able to tolerate, so that was interesting,” said Pamela Hutchinson, a researcher at the University of Idaho Aberdeen Research and Extension Center.

That early finding is welcome.

“Even though the hemp seems to grow fast and is really competitive, I believe that early on we will still need to control weeds right as the hemp is emerging so we don’t have competition from the weeds early,” said Hutchinson, a potato cropping systems weed scientist.

And some weeds such as hairy nightshade “can grow with very little light, such as under potato foliage,” she said. “My hypothesis is the same with hemp.”

Hutchinson said hairy nightshade likely could grow under the lush canopy of a hemp plant — producing berries as well as seed that could germinate and challenge future crops — “which speaks to that early control piece.”

Hemp could be good for potato growers to plant in rotation, one reason weed and irrigation research are important, she said.

Researchers in middle to late July, when temperatures hit the upper 90s, irrigated the half-acre test plot of hemp every five to six days.

Hutchinson said the crop “seems to be doing fine” under that watering schedule, growing uniformly and not showing damage.

UI researchers through future study aim to learn more about ideal irrigation timing and amounts, important partly because they want to find out hemp’s ability to use less water and still thrive.

The hemp plot is irrigated with solid-set pipe on the ground. Researchers recently installed upward extensions to water the plants, which were seeded May 20 and stood more than six feet at the end of July. Hutchinson said farmers instead likely would use an overhead center pivot.

“We had really no idea what to expect here,” she said. “We had been told it will grow to 12 feet.”

UI is growing hemp for fiber. Aberdeen researchers planted at the seeding rate the seed donor, Benton, Mont.-based IND Hemp, recommended.

Most of the Montana crop is not irrigated. Hutchinson said that with irrigation in southern Idaho, researchers through future study aim to learn how to optimize yield and quality.

This is the first growing season Idaho allows hemp to be grown. Hutchinson said the state-licensed Aberdeen trial is small because funding for a larger project was not found and researchers need to learn best field and harvest practices in small areas before moving to larger trials.

She said more work is planned in areas including planting timing, nutrient and irrigation needs, and varieties.

UI plans to work with tribes on hemp research and on related extension education.