Nearly 200 nations faced a Monday deadline to file what the United Nations’ climate chief calls “among the most important policy documents governments will produce this century."

As climate change accelerates, plants face mounting pressure to adapt to shifting ecosystems and environmental conditions. This challenge is especially urgent for crops—plants resilient to drought and heat are essential to secure food supply in an unpredictable future.

Like Mr. Vocoret, Athénaïs de Béru of Château de Béru, believes climate change has created a lot of unknowns. Ms. Béru, whose estate is situated around a 13th-century château on a hill, has been farming biodynamically for 15 years, and organically for 20. But the once-predictable growing season has been disrupted by the changing climate.