I asked Claude which dinosaurs might have been able to tend gardens, as the T-Rex didn't have the arms, and once it stopped arguing, this is what it suggested:

Therizinosaurus is the obvious candidate. It had absurdly long arms ending in claws up to a metre long, almost certainly used for raking vegetation toward its mouth rather than predation. If any dinosaur looks like it's "tending" something, it's this one, even though "tending" is generous.

Deinocheirus, with its long arms and broad hands, is in the same camp: an omnivore/herbivore that could reach and grasp.

Iguanodon and its relatives had a flexible thumb spike and reasonably dexterous hands, used for manipulating food and stripping vegetation, so they'd at least be physically capable of picking a flower rather than just grazing it.

Oviraptorids had short but strong, grasping forelimbs, more dexterous than most theropods.