Two hothouse foundations form the north and east borders of the herb garden. From their construction early in the 19th century, these heated glasshouses were used year-round to grow vegetables, fruit, and flowers from seeds, cuttings, and bulbs. Over the years, other garden structures were added including a grapery, a forcing house, cold frames, and hotbeds. During excavation in 1993, archeologists located a previously unknown cellar in the potting shed in which was the remains of an 1830 heating system for the two glasshouses.