In and around Amiens in the French Picardy region, a stretch of floating farmland poses an unusual challenge to local farmers and gardeners. Les Hortillonnages d’Amiens are an age-old, 300-hectare area of marshland where vegetables and flowers grow on gardens connected by 40 miles of canal. One legend claims that the Hortillonnages date back to Roman times, with the term for market gardens, hortillon, originating from the Latin word hortus. But it was in the Middle Ages that locals mined marshland around the loops of the Somme river for peat…