The scene from the 1982 movie, The Thing, where Palmer burns Child's weed farm didn't make it into the original movie.
According to this question, Palmer sprays the plants with a flamethrower, fearing that they were (or could be) assimilated.
"Don't get near 'em. The plants! They're alive. Those things can imitate anything."
Since that scene is not part of the movie, it's probably not official canon. On top of that, the farm has plants, and we don't know if the Thing infects plants. But is there any canon source that says the Thing could assimilate non-living biomatter (e.g. — food storage, dead dogs, compost, whatever)?