By chance came across two items about pearl millet being grown pretty far north in North America (45°N-46°N), and wondered if those would represent the the furthest north it has been grown.
Pearl millet - Pennisetum glaucum - is one of the millets domesicated in Africa. In this case probably in the West African Sahel (~14°N-18°N). It does well in intense heat with a minimum of rainfall, so it's really at home in the tropics of Africa and South Asia.
The two northern North American locations were the Upper Peninsula of Michigan in the US, and the Province of Quebec in Canada:
- A 2007 article/1 mentions work with pearl millet at the Centre de recherche agricole de l'Outaouais/2 in Quebec, Canada. They were interested in potential use of this plant for ethanol (which I'm not advocating but it is of interest). Also, according to the story, one farmer in Pontiac, Quebec apparently had been planting pearl millet around his potato fields to deter insects.
- Ten years later, there was a pearl millet trial in Hardwood, in Michigan's Upper Peninsula./3 "The 2017 research trial was designed to look at the effect of planting rates and mowing frequency on biomass production.
For comparison, proso millet, which was domesticated and is primarily grown in temperate zones, apparently can be cultivated up to 54°N./4
DO
Notes:
4.
Habiyaremye, Cedric, et al, "Proso Millet (Panicum miliaceum L.)
and Its Potential for Cultivation in the Pacific Northwest, U.S.: A
Review," Frontiers in Plant Science, Vol. 7, 2017 https://doi.org/10.3389/fpls.2016.01961