Caroline Goursat had recently finished training as a flight attendant when France went into a strict coronavirus lockdown, sealing its borders and grounding planes. Days later, the 19-year-old was waking up at dawn to pick white asparagus at a farm in southern France.

“It’s quite taxing,” said Ms. Goursat, who spends half her day bending over to carefully pick the asparagus without snapping off their slender shoots.

Ms....